Finding a lost model

[Cats Eyes]

Introduction

As a result of a number of lost planes that people have reported on the Aerial Photography (http://www.rcgroups.com/forums/forumdisplay.php?f=128) forum, the latest being eBird's All Is Lost thread, a number of us Aerial Photography (AP) pilots got to thinking about ways to locate a lost plane.

Mr. RC-CAM kindly designed and shared a Lost Model Alarm (LMA) device in the thread LoMA: Worlds Simplest Lost Model Alarm. This thread is a spin-off from that thread, which I hope can be a discussion of "plane finders" of all sorts.

Although AP pilots tend to fly higher and "further out" (and in more, um, "interesting" locations) than your average Sunday pilot, the problem of a lost plane is by no means unique to AP. In addition to radio controlled planes, free-flight models and model rockets can use locating devices. In addition, some of the equipment used for tracking wildlife can be adapted as a lost model finder.


Background Info

I'd like to start by sharing some links to information on this topic.

Audible LMA's

LoMA (http://www.rc-cam.com/lma.htm) (Mr.RC-CAM (http://www.rcgroups.com/forums/member.php?userid=5920)) - Audible LMA using a PIC12C508(A)/509(A)
Lost Model Alarm (http://www.designsoft.com.au/ahome/rc/PIC-LMA/LMA.html) (TugBoat (http://www.rcgroups.com/forums/member.php?userid=18284)) - Audible LMA using a PIC12F629/675
A LoMA hack (http://www.rc-cam.com/forum/index.php?showtopic=473&st=0&#entry2754) using a "jogger alarm"
The "Dollarama Special" (http://www.twocats.nicewebs.com/AP/Dollarama/index.html) (Cats Eyes (http://www.rcgroups.com/forums/member.php?u=16610) - i.e. me) - An LMA using an "entry alarm"
KeyRinger (http://www.keyringer.com/) - A commercial "lost stuff" alarm
GWS Be-Found Aircraft Beeper (http://www.aeromicro.com/Catalog/gws_be-found_aircraft_beeper__futaba__1500029.htm) - Commercial LMA


RF Trackers

"Beeping" Tracking Transmitter Kit (http://www.jbgizmo.com/page22.html)
4-Transistor Tracking Transmitter (http://www.uoguelph.ca/~antoon/circ/txtrack.htm)
Mini Tracker (http://www.talkingelectronics.com/Projects/MiniTracker/MiniTracker.html)
RF Tracker (http://members.rogers.com/catseyes/RF_Tracker/index.html) - My own very preliminary investigations into an RF tracking solution
Pointer radars for pets (http://www.pointersolutions.com/eng/pet.htm) - Commercial pet tracker
Walston Retrieval System (http://www.texastimers.com/helpful_hints/walston/wal_cover.htm) - There seems to be very little information about this system on the web! See also here (http://www.shop.com/amos/cc/main/catalog/ccsyn/260/cid/18790).
Rocket Hunter (http://www.rockethunter.com/products.htm) - Model rocket recovery system


Threads

LoMA: Worlds Simplest Lost Model Alarm
LoMA: World's Simplest Lost Model Alarm, Only three parts! (http://www.rc-cam.com/forum/index.php?showtopic=473)
All Is Lost - where this all (sort of) started!
Things I have learned from loosing my plane - Some discussion of LMA's



Discussion

I am hoping eventually to end up with a system that I can use to be 99% sure of retrieving a lost model. To that end, I am working on having both an audible and an RF component. The RF tracking portion should allow me to locate the model's general area (within, say 100 yards), and then audible alarm will then allow me to locate the plane exactly.

If you have lots of money, the above links should provide you with the info you need to purchase the audible LMA and RF tracking system (transmitter and receiver) for a few hundred dollars. I am hoping to do it for much less!

The first three links under RF Trackers, above, show DIY projects in the FM broadcast band. Note that they all use the same one-transistor transmitter output stage. The schematic is identical in all cases, although the particular component values vary somewhat. Since I'm pretty handy with PIC programming, I can use a PIC to drive the output stage with whatever signal is needed (both on/off and perhaps to provide an audible modulation signal). It is my hope to build something like this for the transmitter, use a cheap FM receiver, and build some kind of directional antenna to use to search for the model.

Unfortunately, my knowledge of RF is rather limited, and even with poring through a couple of ARRL (http://www.arrl.org) books, I am still pretty clueless about how to go about building a directional antenna.

If you have any ideas about this, or have any comments on any of the above, please feel free to post away!

-- Kevin

[Cats Eyes]

From the old thread...


What happens if the plane has the speaker pointed upward in the top of the plane and the plane crashes upside down with the speaker pointing toward the ground?? How much sound is lost, how much still radiates outward?

It seems multi-speakers, maybe with less volume, generally would be more effective in the "real world". I've not seen any multi speaker designs that would minimize plane orientation and allow greater coverage. Anyone want to prototype this out?

A very good point. The construction of most piezo buzzers is just a flat disk diaphram, so the sound should be radiated out the back of the disk as much as the front. Most cases are designed to limit the back wave while letting the front wave out. However, I think by hacking the case you could design it in such a way that the back wave could be let out as well, making it bi-directional. That way, no matter how the plane lands, at least one of the "beams" should be directed upwards.



it wouldn't the simplest loma any more but free-flighters use
173 mhz as a uk legal model -borne rf tx.
a 3v lithium coin cell will last 2 weeks.
( 150'ish mhz is used as a non-legal uk freq!)
car key fob lock transmitters on 433mhz uk (350'ish mhz in us?)
can also be used legally
a f/f tx type approved in uk costs ~£50 ready to go
'surplus' tiny 173 xtals are available in uk @ £1
a 1 transistor tx circuit will give usable range
uhf key-fob tx's usedto be ~£10 don't know current prices
add a cheap scanner or a de-luxe free-flighters rx @ £350 (they really are very good
if you can afford) and away you go

Thanks for the info. I would be curious if you could find construction information on these tx's.

£350 is way out of my budget. What did you have in mind as a "cheap scanner"?



I have one of these security alarms that is supposedly 130db that I had a play with, but most of the sound comes from clever construction of the casing around the piezo.
Once you remove it it is not much louder than the std ones.....

I have found that when mine is pointed up in the air it is a lot less softer than when directed at something about 2-3 inches away that reflects the sound again. When I stuck mine to the fuselage side directly under the wing it was suddenly heaps louder.

This concerns me a little. I noticed that my entry alarm seemed louder with the case off. I wonder how much the case and nearby objects affect the radiated sound (direction as well as absolute loudness). I guess this is something to experiment with further.



the tracker tx in the photo is intended for f/f
....
give me a week or so and i'll try it

Yes, I'm very curious about this! I do hope you'll let us know how your testing goes.



the circuit is from wildlife radio tagging by r e kenward
its an idiot guide for biologists so it gets pretty basic but is a super book if you can get it.
there's another one by d w macdonald and c j amlaner jr
i think the title is 'a practical guide to radio tracking'
this is a collection of sym posium papers i think
the basic circuits have been around since the '60's!
ther's also an article in the us national free flight society 1995 symposium report
by ken bauer which details his commercially produced design.
i will scan a few to get you started but they're all pretty much the same.

I had a look around for those books. Our library doesn't have them. I checked Barnes & Noble and Chapters (the Canadian equivalent of Borders):
A Manual for Wildlife Radio Tagging
by Robert Kenward
Chapters (http://www.chapters.indigo.ca/item.asp?Item=978012404242&Catalog=Books&Lang=en&Section=books&zxac=1): C$47.50
Barnes & Noble (http://search.barnesandnoble.com/booksearch/isbnInquiry.asp?userid=0Y3q8MMAzQ&isbn=0124042422&itm=1): US$72.95
Strange B&N is so much more expensive! :confused:
A Handbook on Biotelemetry & Radio Tracking: International Conference: Biotelemetry & Radio Tracking in Biology & Medicine, Oxford, 20 - 22 March 1979
Editor: Charles J. Amlaner, D. MacDonald
Chapters (http://www.chapters.indigo.ca/item.asp?Item=978008024928&Catalog=Books&Lang=en&Section=books&zxac=1): C$560.50 :eek: (out of stock anyway!)
Barnes & Noble (http://search.barnesandnoble.com/booksearch/isbnInquiry.asp?userid=0Y3q8MMAzQ&isbn=0080249280&itm=2): price not given, out of stock
I may spring for the Wildlife book if I don't find the info elsewhere. Any chance you could scan some of the relevant pages and post them? I was hoping to do the whole thing for under $100 and if I have to spend $50 on a book that blows half of it right there!

The transmitter is one thing, but I'm still clueless about how to go about building a good direction-finding antenna. I think a good antenna design can not only provide a way of figuring out the direction to your model, but can also increase the range by several times. I just don't quite know where to start.



Hey Kevin - I found some of those units at our local $2 shop. Took two home and wow - ear splittin sound from it. I can see how you could hear it 200m away!
You are correct, it does use a voltage booster out to the piezo. I measure around 30volts AC!
I am busy modifying it to see how light I can get it. Removing the reed switch and trimming the pcboard all around. Will post some pictures once done.
I am going back tomorrow to get the rest of their stock :-)
Mark
Great. Keep us posted.

I'll have a look at the output of the voltage booster transformer with the 'scope next time I get a chance. I'm curious how much the voltage is boosted. It appears the transformer primary is just switched on/off (at the audio rate) across the battery supply, so perhaps by changing that to a push-pull arrangement (H-drive) you could double that.

Another thing I want to try is an driver element I pulled out of a defunct smoke alarm. It's about 1.5 times the diameter (twice the area), so theoretically should produce more sound still.

Keep the great ideas coming!

-- Kevin

[Mr.RC-CAM]

I've been thinking about an RF solution for the last few weeks. I have a some strong opinions about what would be effective and practical. Over the winter I will try to bring it to life.

Here are some of my thoughts:

(1) Range: I'm aiming for 300 meters (or more) of reliable range.

(2) Low Power: It will need to work for at least one week on a small dedicated battery supply. The Tx will be activated upon loss of the R/C signal.

(3) Frequency: The solutions that use the FM radio broadcast frequencies are not the ideal choice, at least not for me. Although the Rx would be very low cost and off-the-shelf, the poor sensitivity and tuning stability of the average FM portable radio would be an issue. Also, effective and compact directional antennas would be a challenge at 88Mhz to 108Mhz. Lastly, the longer range I am looking for would violate the FCC's requirements (Tx power on FM broadcast freqs would need to be VERY low).

So, my target is 433Mhz. There are advantages to this spectrum, including antennas that are smaller and the higher frequency offers increased directivity (something we need).

(4) Legal Operation: I'm in the USA, so I'm going to do what I can to create something that does not violate the FCC regs. There are provisions for home built devices, but they will be tough for the average (RF naive) hobbyist to ensure compliance. If I cannot create a "legal" license free project, then second best is something that can be used by a licensed amateur radio hobbyist.

(5) Ease of Assembly: This is the part that is slowing me down. I have learned that most folks will tolerate a small amount of soldering, but will skip projects that get too involved. So, I'm looking at existing consumer devices to hack, mostly key fob based remote control accessories. If I get lucky, this will also go a long ways to satisfy the FCC issue.

(6) Cost: This is a tough one. My experience suggests that if the project goes over $35 USD then the target audience will be quite limited. But, that bridge will be crossed when the cost data is known. The reality is that Tx will probably be under $30, but the Rx cost is a wild card at this point.

(7) Small size: I wish I could say it will be weigh 1 gram. But, to meet all the things listed above, it will probably be 1 ounce or more. It would be less if it is designed for ham radio users. But I will first aim for the license free solution.

RC-CAM

[zl3vml]

Thanks for the new thread Kevin.
If you have a scope (or access to one) - measure the frequency of the AC into the step-up transformer. My guess is it would be maybe around 25-35 KHz. That would explain the small size of the transformer. I used two 3v lithiums, 6v to get the measured voltage of 30v. Current draw was around 78mA.
I tested the alarm part today and could hear it right accross the field, did not measure the distance as it was more than I need, a couple of hundred meters I would guess.

Now to work on the PicAxe drive circuit. I think I will glue the chip onto a piece of 1/32" ply with the legs splayed and solder the components directly to it.

Mark

[zl3vml]

Here is a photo of the alarm (bottom) and after some prudent trimming of the pcboard (top) with the weights.

This is only the alarm circuit. The PicAxe timer circuit is yet to be modified and "slimmed" down.

Mark

[zl3vml]

Err - can someone tell me how to get a smaller size photo? It is compressed down to only 67kB but still comes out so huge on this list - or is it just my browser?
Guess I should set my camera to a lower resolution....
Mark

[GailInNM]

RC-CAM,
I have been playing at 433.92 MHz for quite some time now. There appears to be very few loopholes in the FCC regulations for unlicensed operation there and that will restrict the range considerably if operated legally there. Radiated power and on time restrictions under part 15.206 are the most restrictive. There are many devices on this and similar frequencys that are being sold that violate both the regulation and spirit of the regulation, but that does not make it any more legal for us to do it.

I chose 433.92 MHz as there is a large amount of equipment available on this frequency, and it is within the 70 cm Ham band. With the Technician class ham license so easy to obtain as a result of the rule changes of a few years ago there is no reason for anyone in the US to have to operate illegally. Also many overseas courtries specifiy 433.92 MHz as a specific frequency with rules that are much less restrictive than the US regulations. Of course that varies country by country.

For ham operation this is good news. There a a number of transmitter RF modules available that are intended to be built into end used devices. The small ones have about 10 to 15 mw outputs. If this is coupled to a somewhat resonant antenna, ie 6.7 inch chunk of wire, the field strength greatly exceedes the field strength perimtted for unlicensed operation, however it is no problem for ham operation. The recommended mode of operation for using these module in unlicensed mode for key chain type contollers is to put what ever type antenna they can fit in and then put an attenuator between the module that just brings the radiation within the FCC field strength limits.

I ran one of the 15 mW modules on the bench using a function generator for modulation. Ran it on 5 volts, but the operating voltage range of the module is from 3 to 12 volts. Used a 6-1/2 inch wire antenna. I walked down the street using a using a handi talkie with an AM detector in it and got 600 feet out before the signal started getting into the noise.

The module I was using was a Radiotronix RCT-433-AS. It weighs in at 1.25 grams and gets a little lighter when the connection pins are cut off short. Size is approximately 10 x 13 x 6 mm not including the connection pins. The modulation input directly keys the transmitter in what is normally refered to OOK (On-Off-Keying) and keys the entire transmitter so no power is consumed by the transmitter unless a positive signal is applied to the modulation pin.

Companion Receiver modules are also available. The least expensive is a super-regen with a RF amplifier to provide isolation isolation between the regen detector and the antenna to keep the radition from the detector low. It has excelent sensitivity, sub 1 microvolt. The one I have played with the most is the Radiotronix RCR-433-RP.

Since we are always concerned with cost, the good news is that these are low cost modules. The lowest prices I found were $4 for the transmitter module and $5 for the receiver module is quanity 1 type pricing. They are available from many sources, but I got my last ones from Mouser Electronics, www.mouser.com. Also similar modules are available from other manufacturers at similar or slightly higher prices.

I think that when used for a Lost model locator, that operation classification would be as telemetry under the Ham regulations and this requires that the transmitter send ID every 10 minutes. But, this ID could be sent contnuously as an A2 Morris code as used for your DF locating tone.

As an aside, I also have a RC Transmitter built up on 433.92 MHz running 500 mW power and have used the above modules for telemetry on a Hummingbird electric micro helicopter. But these are topics for other threads if any one is interested as I have already used up more than my share of this thread.

Gail -- W5MLY

[Mr.RC-CAM]

GailInNM, All of your points summarize the issues. The FCC compliance is a tough nut to crack. I have some Lynx modules that are part of my backup plan, but like your Radiotronix solution, they would require a ham license to operate.

My psuedo-FCC compliant idea is based on using a stock key FOB. These low power devices could achieve 300 meter range with the proper antenna on a Rx that has good sensitivity. For example, my Ford's remote gives me 75 meter range in a crowded parking lot. With a 12dB Rx antenna I could stretch that to nearly 300 meters.

Hacking into the FOB would be a technical violation for sure. And the signal's expected intermittant use would exceed that which is allowed (it would be activated every 30 seconds or so). But, in the spirit of the FCC rules it would be something that might not be so offensive that it draws a lot of unwanted attention to it.

By the way, I search for FCC ID's to the RF devices described in the first post. I could not find any. Does anyone have the Reg ID for the Walston device?

RC-CAM

[CraigF]

Has anybody checked out any other of the model rocketry (and HPR) location devices, besides the Walston? These are also typically very long range, since the models are unguided, have battery life that occasionally lasts for > a month, and of necessity are quite rugged too. Then there are the GPS-based units that transmit their coordinates...

The Walston has been used for many years, legal for sure in the U.S./Canada, was once the Cadillac of location devices, don't know if it still is. IIRC Walston has virtually zero formal web presence, they used to only accept orders by phone/mail, mainly just advertise in rocketry mags. All my good info/reviews on it are in print form, and of course I can't lay my hands on it when I want it...you could call them.

Re the wildlife tags: I can sometimes pick some up from home with my handheld scanner, course I don't know where the animals are exactly, but they're *supposed* to be around 5 miles away (where their habitat is)...so range isn't bad considering their small antenna.

Many radio location methods are described in the ARRL (annual) handbook. Everybody who has any interest in any electronics should get this book at least once, it's the best bargain out there for reference, even if you're not interested in ham radio. When the new year issue comes out, the previous year's is dirt cheap, you won't be disappointed.

[Cats Eyes]

Well, it looks like we've got quite a good discussion going here! Thanks everyone for all your input and ideas.

Mr.RC-CAM: I'm very glad you've chosen to tackle the RF tracker idea. Your list of requirements will certainly make it a challenge. You certainly seem much more aware of both the technical and regulatory issues than I am.

I "chose" the FM broadcast band rather by default -- the only schematics I'd found on the web were for the FM band. Plus the idea of using an old FM radio (I have two just "floating around") appealed to me. However, I'm certainly not married to the idea if something better or more practical can be found.

As far as I can tell, spectrum allocation and regulation is harmonized between Canada and the US. ("Harmonized" being a euphemism for "the US does what it wants and Canada follows suit"!) However, I'll try to find the Cdn regs and check to make sure.

For my personal requirements, you could certainly relax the "ease of assembly" and to some extent the weight and cost requirements. I was born with a soldering iron in my hand, and my brushless Slow Stick won't mind an extra oz. of weight. And since this is supposed to protect me from losing a plane worth, well, more than I care to think about, if I have to spend $100 or so on the solution, I'm willing to do so.

What I mean is, in the course of investigation if you come up with a good solution that is a bit more difficult to build, more expensive, or weighs a bit more than you had hoped, please share it with us anyway!

* * * * *

zl3vml: I hooked up the 'scope to look at the output from the step-transformer. With the piezo element connected, my AC voltmeter measured 26 volts (rms). I removed the piezo element for the rest of my tests to avoid driving my wife (and me) crazy and instead connected a 1.8K resistor. The attached pic is with resistor attached and is at 50uS/division (horiz) and 20 V/div (vert). Sorry the pic is so crappy, but hopefully you get the idea.

The frequency slides quickly up and down for a kind of "warbling" sound. The multiple tracings on the right show where the frequency is sliding through the range. I measured the period as going from 0.245mS to 0.455mS, or about 2.2 to 4.1 KHz. My guess is they do that for two reasons:

To make sure it hits the driver's resonance at least once per "cycle" (avoids having to deal with manufacturing variations), and
it sounds distinctive.

I think my batteries are getting old, so I was supplying the circuit from 4.5V regulated. At that voltage, it was taking 83mA. I haven't tried increasing the supply voltage; another thing to try.



Err - can someone tell me how to get a smaller size photo? It is compressed down to only 67kB but still comes out so huge on this list - or is it just my browser?
Compression has nothing to do with image size (number of pixels), just the size/quality of the resulting file. Yes, it's huge for me too. If you can't resize in your camera's software, go get Irfanview (http://www.irfanview.com/) (it's free), then use the resize/resample (resample is better quality) and type in whatever size you want. When you save, you'll have to check the jpeg compression ratio (under options) to make sure you get a small file too. For instance, I've resized to 640x520 below. Hope that helps.

Incidentally, how did you hack your case? I mean what tool did you use to cut the plastic? I thought that was clever to keep the battery compartment -- think I'll steal your idea!

* * * * *


Has anybody checked out any other of the model rocketry (and HPR) location devices, besides the Walston?
I would dearly love to, if someone can give me a URL. The Walston (which as you say has zip web presence) and the Rocket Hunter (http://www.rockethunter.com/products.htm) (at tad pricey for my tastes) are the only ones I know about. If you know of others, please post the info.



Many radio location methods are described in the ARRL (annual) handbook. Everybody who has any interest in any electronics should get this book at least once, it's the best bargain out there for reference, even if you're not interested in ham radio. When the new year issue comes out, the previous year's is dirt cheap, you won't be disappointed.
I had one of those out of the library and read through the section on Radio Direction Finding (RDF). It was a bit over my head, but when I read it I didn't have any particular frequency or anything in mind. Perhaps if I decide (or someone else recommends) a particular frequency, I can read up on antennas for that frequency specifically.

If I remember correctly, RDF transmitters are frequently on 144 MHz. Could we use that?

-- Kevin

[clipclop]

Heres a higher power FM beeper cct, should give 200M to 1 km depending on instalation and possition of downed model .
Stewart

[zl3vml]

Kevin - thanks, can resize the image size on the camera. Just lazy :-(
I used a Junior Hacksaw to chop the case. Need to take care as the plastic is slightly brittle and tends to splinter.
Just a note - some of the comments above were not posted by me - dues to go to someone else.
Ok on the frequency - I would have though it much higher.
As an aside - dont touch the that output circuit while it is going - has quite a punch in it!
Mark

[CraigF]

Kevin: I also was "born with a soldering iron in my hand", so some of the things I do for fun or challenge might be a real PITA for most...probably not useful for this discussion. I also don't mind doing some firmware etc.

I have not kept up with rocketry stuff much, things got tough for me after 9/11 because I have to get most stuff from the U.S. ... so I don't know what's current, but transmitting GPS coordinates was coming on, big rockets are expensive and travel a long way. Old GPS receivers are fine, and cheap used, you want the NEMA output models that put out ASCII text, that's what's transmitted, not that large when the case/keyboard/display is removed. For larger planes, but don't have to be huge by any means.

Cost effective stuff is modifying existing gadgets. I just used a Radio Shack very loud beeper ("personal alarm") in my rockets, modified to only beep every 30s to conserve battery, lasts a very long time. These don't exist any more I think, used to always be on sale for cheap and quite strong, not to mention annoying and loud, their purpose. As others have mentioned, these are NOT loud when the electronics are removed from their plastic case.

Modifying RF stuff is much more restricted in the U.S. than Canada. The basic mod for most Tx modules is a bigger antenna or an RF amp on the output. Not legal. You can only do so much with a weak signal without getting fancy (like for GPS reception).

For many reasons, AM may actually be better for this than FM. Due to FM's line-of-sight reception...we need range here, and to be able to get the signal out when there's obstructions. AM responds quite well to a rotatable loop antenna, for RDF. BTW, when researching on the web, RDF and "fox hunting" are ham terms that may be useful. Many of the gadget Tx are FM specifically because of their natural LOS range. We don't want LOS, if we did we'd walk straight to the model, or at least head in the right direction.

[clipclop]

AM or FM makes no difference as to if its line of sight , its the frequency used . higher frequencies are line of sight - lower not so .
Your FM radio works in your house ? in cities ? the advantage of FM over AM is it generally needs less power to get the distance , its a more efficient means of transmitting . the cct posted above should get 200m with only a 10" antenna fitted .
Stewart

[CraigF]

Not true!

[Don't get the wrong idea, I only use FM myself. But AM sometimes has some advantages. Especially for distance.]

[Mr.RC-CAM]

AM broadcast radio has longer range over FM broadcast because of the lower operating frequency and their typically higher RF power. The reduced bandwitdth of AM can increase range, but I doubt it would be noticeable to the average fellow. Overall, if the AM vs FM were on the same frequency, and all other variables remained the same, then the range would be similar.

RC-CAM

[CraigF]

clipclop: Apologies for my curt response! I don't know what I was thinking...for some reason, I think AM is more efficient than FM, and CW even more so. (Bandwidth??) IOW, less RF pwer gets you more (potential) distance, with the proper antenna. This is probably not true, and is only in my mind because of the circumstances that I've used them. And yes, as you said, it is the lower frequencies that have the opportunity for longer range, all other things being equal.

In any event, we are legally limited to what mode/power/frequency we can use, so not much use me getting philosophical about it, better to think of what's possible and available.

Here's an odd off-the-shelf thing that came to mind: those transmitters they have for people skiing etc. in potential avalanche areas, for locating people if they get buried by snow. I guess (as usual) it's the Rx that's important here, and the ones for this are supposedly pretty effective at pinpointing...have no idea re cost...the Tx's are quite small and it's those that I usually see sold.
Edit: well, that was a dumb thought. Though the receivers are pretty accurate, they cost a small fortune, probably more than the model. The range of the Tx is not enough either.

[Cats Eyes]

clipclop: thanks for posting that schematic. I'm assuming the first transistor is an audio frequency oscillator which provides an audible modulation to the RF. The second transistor is the RF oscillator and the third is an amplifier. Is that right?

zl3vml: I'll try the Junior Hacksaw approach. I was thinking you might be using a hot wire or something. The edges look very clean to me. I guess your hands are just steadier than mine!

Not sure why you thought the frequency would be higher. The output (secondary) is connected directly to the driver element so it has to be at the audio frequency.

CraigF: your Radio Shack personal alarm is probably the same as the dollar store alarms that Mark and I are hacking. Next time you're in a Dollarama or a Zellers have a look for either entry alarms or jogger alarms.

Your discusison of GPS coords etc. is a bit beyond me at this point. I'm not sure how transmitting GPS coords is any advantage over transmitting straight carrier if your TX/RX combination doesn't have the range? Or were you transmitting to a satellite or something?

As far as transmitting on the AM band, I had not thought about that as I just assumed you'd have to get a heavy loopstick coil/antenna (as opposed to winding a couple of turns around a 1/8" drill bit for the coil and hanging a bit of wire off your plane for an antenna). But I'm willing to try it if you come up with a schematic.

You mentioned beacons that skiers use in case of avalanches etc. Are you talking about Personal Locator Beacons? By a wierd coincidence I just happen to have worked on the web site for registering these things in Canada. See Canadian Beacon Registry (http://www.nss.gc.ca/site/cospas-sarsat/emergencyBeacon_e.asp). If one of these babies goes off, you'll have Search and Rescue helicopters combing the area looking for someone to rescue. When they find out they're just looking for a lost model plane, you will be in deep do-do! No, you were probably thinking of something else.

-- Kevin

[zl3vml]

Kevin - I had the case on the grindstone to get a smoother edge and then cleaned up with a hobby knife.
Have now re-programmed my PicAxe to power the alarm via a transistor and it works.
Three options - 20sec (for testing), 5 min & 8 min selectable via link.
Now I just need to build it over on the back of the chip - that's gonna be fun!
Thinking of trying smt components glued directly onto the top of the chip and also sticking it inside a bit of heatshrink.....
Mark

[rkhoo]

Hi, I have lost my plane a month ago and thus gave some thoughts about Lost Plane Locator devices.

Idea #1: How about a Smoking device that is triggered by radio signal lost or by ch6. When the plane is down, polit can use the radio to trigger the somking device to release a colored smoke. That will aid polit to locate the lost plane. If in windy condition, the smoke trail will point to the plane as well.

Idea #2: Use of CB radio (those cheap walkie-talkie that sold for $30 a pair) as an audio-aid to tell if polit's search path is in-line with lost plane. Strip CB to make it lite and install it in plane. When radio is out, or ch6 is in use, a device will use the call/beep button on the CB to send a signal to a CB held by the polit. Since our TX's antenna's range is somewhat weaker if we point the TX at the RX, this behaviour will cause our device to send call/beep signal to the CB held by polit. All the polit has to do is point the antena around until he/she hear a beep from his hand-held CB. This device will help polit to walk along the path of the lost plane.

Just my 2 cents :)

[CraigF]

Kevin: Transmitting GPS coords means you don't have to search much, and it means you don't need a fancy DF receiver...it's the DF Rx that makes devices that work well, like the Walston, so expensive (not to mention a bit unwieldy to carry/use). This is a big DIY project, it has been done, not that cheap. Though I can think of current off-the-shelf stuff that would make it a lot cheaper now than the ones I read about a few years ago. I'm not recommending this method BTW, just mentioning it as a method that tells you exactly where the plane is, as opposed to you having to go on a "guided" search. Also, these devices were in rockets. GPS coords were sent every little while (maybe 10s) since the Rx then were pretty slow to update and put out (serial ASCII) data...you'd know where the last known position of the rocket was, JIC the rocket/GPS did not survive landing. Plus you get good Tx range while rocket is transmitting while in the air, not as good range when it's on the ground transmitting, but you'd have its last known pos that you received to go to, useful for rockets that are coming "straight" down (chute failure etc.).

When I mentioned AM before, I was thinking LF. I am *not* experienced in RDF, have never tried it. It's just that typical FM bands, the signals are reflected etc., so RDF is apparently trickier. But we'll be searching in open spaces, so that's good. But not so good for line-of-sight if you've maybe lost a glider, considering where they might fly (hills).

I'll look for those Walston articles, will take a while, lots of mags, I don't even remember which title. It's worth paying attention to a system that's known to work very well, learn from it. The Rx and its antenna is the big thing, you don't need much transmitted power, that's important for Tx battery longevity and legality. As most probably know, a Yagi ant is rather directional, and that's what Walston uses. The advantage is you can easily make one, or buy a cheap one and mod for use...good directional ones are quite large until you get into the higher frequencies. I don't know what higher frequencies are legal for non-hams these days, besides the obvious cordless phone ones (I mean for general use).

There are lots of plans for "foxes", Tx that are used by hams for "fox hunting". This is essentially what we want to do. But on legal frequencies to the unlicensed, which means pretty limited output power. The techniques should be identical for us, though much of RDF success depends on experience...it's meant to be a skill challenge. We want it to be easy...

Re the avalanche radios, no I was not thinking of the beacons. That would be a problem, as they use international ELT frequencies, definitely illegal. I was thinking of the LF ones, think they use 457kHz these days. Range is usually less than 200m though (some much less), fine for their purpose but not for us.

Edit: Did some looking. Didn't find what I was looking for yet, but some other stuff. In the ARRL books, lots of hard info, for sure not for beginners. Checked out some other RF device info, and they basically say, if you want anything half decent that really works, get a ham license! Easy enough in the U.S. for the lowest level, a little more work in Canada as there are fewer levels now and the lowest takes some effort (and your license is "permanent"), but you don't need code. The Walston has a reported range of 30 miles in the air, 3+ on the ground, Tx weighs 7g. You're talking around $500+ for the basic system. Cheaper systems require a ham license: Adept makes one system for about half the Walston price, 20 mile air range and 1 mile on the ground. There's even one system that uses radar! Cost is $50 for the Tx (radar pinger), and you-don't-want-to-ask for the receiver!

I am pretty sure you could make a GPS coord Tx and Rx for less than $600, using off the shelf stuff and some DIY/ingenuity/sweat. Some day there will be one premade for us. The advantage of transmitting the plane position is that you don't have to develop RDF skills or get into using fancy DF receivers. "All" you basically need is (over-simplified and not legal/practical for us, but the idea):

GPS ASCII out->text pager Tx-----------------------text pager Rx->go to GPS coords and pick up model

By "text pager" I mean the functional equivalent, not tied to a cell network that may not exist where flying.

Or: You can get an older GPS unit with ASCII out for $30 easily, nobody wants them, strip the case/display/KB, pretty light. Magellan 2000/3000 would be OK ones to look for, say. RF modulators that accept ASCII input are cheap, used for ham packet radio. The Rx I haven't thought about...though the demodulators to get the info out of the RF are cheap/simple enough, you'd need a small computer/handheld to process/display the data , or a dedicated equivalent. Doable with a micro and display, doesn't have to be fancy. Heck, the plane Tx could transmit tones even, rather than ASCII, Rx tone decoder converts tones to numbers on display, plus you'd have an audio output while plane is flying to know everything's working.

I buy junk gadgets when cheap, for "modifying". I picked up call display units from Wal-Mart for $3 each. Guess what, they take 1200 baud (??, forget) ASCII input and display numbers, like in coords. That could be your Rx display, once you demod the RF ASCII (plus maybe a little other stuff...). What I mean is, we can maybe get something very useful for fairly cheap using hacked gadgets. Somebody just has to think about it and give us some direction. I gave up on the RDF location idea a few years ago as ones that really worked well were pricey, way more than my models at the time. So stuck to audible ones. For me, the next step up, after having to search for a model by whatever means, is NOT having to search for a model, and that's what I really want. Mr. Plane tells me where he's hiding.

[Cats Eyes]

Okay, how about the CB band, as rkhoo suggests? Anyone else thought of that? I think it's around 27MHz, right? I think you can run 100mW without a license, and 4W with. Getting a license is not like a ham license, 'though. Just fill out a form and send in your $. I haven't done anything with CB since I was in my teens (longer ago than I'll admit to anyone), so I don't know if anything has changed.

The smoke idea sounds a bit far-fetched to me, but you never know. It could get someone thinking on some lines they might not have thought of otherwise and they might come up with something practical. Lateral thinking I think the call it.

I've also heard the idea of tying a 20' streamer to your plane. I think that was mainly for visibility at altitude, but it would help enhance visibility on the ground, or in a tree. Didn't I remember someone suggesting attaching something smelly to the plane and using a dog to "go fetch"? :D

CraigF - Thanks for clarifying. I see your point that if you had GPS coords you wouldn't need to do any "direction finding" as long as you could pick up the signal. I also like the idea that you could transmit while in the air, and even if the plane ended up in a ditch or was unable to transmit, you could still capture the "last known position."

I'm very curious about the call display units you mentioned at Wal-Mart. They take ASCII serial input? For $3! :eek: Please tell us more!

zl3vml - How are you controlling the alarm from the PIC? Are you having the PIC turn power to the alarm on/off? Or are you using the point on the alarm where the reed switch is connected? Does your transistor short across the reed switch? I was thinking of doing it that way, since if the external power was lost, the alarm will still sound.

How are you powering the PIC? From the alarm battery or the plane battery? On my testing device, I was having a problem that the alarm batteries were getting low and the PIC was resetting. That would turn the alarm off and the batteries would recover. The PIC would then power up and set the alarm off again. To get around this problem, I was going to power the PIC from the plane's battery, but that would mean I would have to have the PIC actively hold the alarm off (via an external transistor, for example), so that if the plane's power was lost the alarm would sound.

You mentioned 5 and 8 minute delay. What happens after this time? Does the alarm then sound continuously? I was thinking of having it intermittent, say on one second out of ten, to prolong battery life. I also thought about having the plane's battery power the alarm if it's available, and fall back on the alarms own battery only if the plane's power is lost.

I was also thinking of hooking it up to a receiver channel so the pilot can trigger the alarm on command (assuming the receiver was powered up and functional). If the signal is lost (either because the transmitter is out of range, or the receiver isn't functioning), then it would default to sounding the alarm.

Anyway, it sounds like you're getting this thing built a lot quicker than I am! Keep it up and let us all know how it goes!

-- Kevin

[zl3vml]

Hi Kevin,
Both the alarm and PicAxe are powered from the two lithium cells. No other battery as it is for a freeflight model - no radio. There are a few circuits around that run off the receiver and will sound as soon as you turn your transmitter off, but no good to me in this application.
I have removed the whole reed circuit off the board. The PicAxe output goes high which turns the transistor on which feeds power to the alrm cuircuit. The output pin is pulsed a few times every minute, so the alarm gives a few warbles every minute only.
I reckon the batteries will last a good day or so if the plane is lost, but basically, when the plane is launced the switch is set on and the 8 minutes will time out and start pulsing the alarm every minute. When the plane is retrieved the switch is turned off.
Now, in general use, the plane will be retrieved a lot quicker as the dethermalizer is set to go after 3 minutes. Should the plane get into a thermal or get quite a bit of drift before the DT operates it could land behind or in the Pine forests around our field after it DT's, then after a few more minutes the alrm will be activated by which time I will be on my way to hunt for it. The theory is that the alarm will guide me to directly to the model by pinpointing the pulsing alarm. Very usefull when hunting in the trees or bushes for something you know is there but cannot see and not sure exactly "where".
Hope that the above explains a bit more?
I sourced all the components today in SMD so will get some this week and try to build the whole circuit of the timer on the back of the 8 pin PicAxe.
By the way - the PicAxe is a std Pic chip with a bootstrap programmed into it. It reads three of it's pins for programming so you can program it in circuit without having to turn power off or use a programmer board.
Cheers - Mark

[CraigF]

Kevin: Re the call display units, they were clearing them out for $3, and I still see them there for Cdn$8 reg. price, probably a newer internal design but looks the same, so it's not like they're expensive (brand AudioLogic). Work off 6VDC. My point is that modding off the shelf stuff is much cheaper than custom design. Like where can you get a serial input LCD display for Cdn$3-8? When I really look hard at some of the custom gadgets I've built, they cost a bloody fortune, $ by $ spent over the development, not all at once so I don't notice the overall cost so much. Then compare with the sophisticated stuff (that doesn't do what I want!) that costs relatively peanuts.

I don't have my info to the call display units handy, but it's pretty much the same input format as you'd get from a (1200 baud, IIRC) modem, so it's not "pure" serial ASCII, though it's not like it's secretly coded data. I have a "Circuit Cellar" article on this stuff and the data format filed with the call display units, haven't played with them yet, just looked inside, didn't get them that long ago. Like for many Canadians, the "building season" is just ramping up...

Whatever is transmitted, the crux is a good Tx of decent power, legal, and then a good Rx. As basic as this sounds, it has always been my stumbling block when thinking of these location devices. I did not want to get into something that only hams can use, because that really limits the community of involvement for help and ideas. You see, as a ham, I really don't know what the rules for non-hams are, I just pay good attention to what our rules are because they are strictly enforced (even moreso by hams than by "the law"), as nobody wants *privileges* to be abused and then lost by everybody because of non-conformers. You would be surprised how quickly an "illegal" is tracked down by local hams, triangulated and RDF, they see it as a challenge as well as a duty. Actually, it *is* fun...

Edit: to clarify some previous ramblings. I mentioned transmitting tones...I meant DTMF (touchtone) because we're transmitting numbers (GPS coords) and chips to generate/decode them are cheap and common. As for cheap off-the-shelf Tx/Rx, how about guts from FRS radios? Not much power, but maybe enough for some uses, maybe with a hopped-up Rx. I've seen low-feature pairs of these going for Cdn$30...we don't need all the features and the fancy brands on the cases, and we can add better Rx ants if that helps. Don't know how RDF would work for these, but I'm still largely thinking of transmitting data. Oh yeah, I keep saying "cheap" because I break these gadgets open and sometimes I can't do what I want, and by that time they're useless for their intended purpose...

[Cats Eyes]

Mark -- sorry, I forgot you were doing this for a free-flight model. So you don't have a choice -- you have to power it off the same batteries as the alarm itself. You may end up with the problem I described above, except worse. If the batteries go too low, the PIC will reset, which will then start the 8 minute timing all over again. You might want to think about putting in a large capacitor to keep the PIC powered even if the alarm current drain causes the battery voltage to dip. This should work if you keep the alarm's "on" time short. Then again, you're using different cells than I am, so you might not have the same problem. I should also check the brown-out reset setting in the PIC configuration. I think I have it set, which I probably shouldn't have!

Other thing I wanted to mention was that I was using a PIC output pin to trigger the alarm, rather than switching the power to the alarm on and off. The reed switch in the original circuit was connected to ground to silence the alarm, and the alarm would sound when the switch was opened and allowed to go high. Connecting a PIC output pin to this point meant that I could trigger the alarm with a "high" output on this pin and silence it with a "low" output. That saves the external transistor that you are using. If this is confusing, I think I described it a little better on my Dollarama Special (http://members.rogers.com/catseyes/Dollarama/) web page. Scroll down to the section Alarm field tester.

I looked at the PicAxe web site a while back. Very clever. Perhaps if I were starting from scratch, I would go that route. However, since I already have a programmer and lots of PICs floating around (in a fit of exuberance I bought a tube of 25 PIC12F629s), I don't think it's useful for me. Note that regular PIC's can be programmed in-circuit as well as long as you give a bit of thought to which pins you use for what.

* * * * *

CraigF -- Thanks for the info on the call display units. I don't exactly know what you'd pay for a serial display unit from Digi-key or such, but it would definitely be much more than $8! I'll have a look next time in a Wal-Mart. Even if I don't have a use for it right now, it will be fun to play with. :)

Hey, you've given me an idea. Why don't I make a really dirty, noisy powerful transmitter that sprays static and junk all across the spectrum? In no time, I would have dozens of hams helping me look for my model! Of course, this would only work once, and they might not give me my model back at the end. :D

Seriously, I don't want to get in trouble with the hams, or anyone else. I would like to stay in the regulatory bounds as much as possible. Note that I hope this thing will be used very infrequently. In fact I was sort of thinking of not even activating it for an hour or two to give myself time to try and locate it by other means and have the RDF TX kick in as a last resort.

Do you know what kind of cost we're looking at for the GPS coord transmitter idea? What does a cheap GPS unit go for these days anyway? It would have to have ASCII out, right? Then as you say DTMF encoder at the TX end and decoder at the RX end. The display, at a minimum. Probably want a PIC or Basic Stamp or something in there to "remember" the coords that were transmitted and re-display them when asked. Plus of course the TX and RX themselves. Somehow I don't think you could do all that for under $100. But then, maybe it just can't be done (at least with any degree of reliability) for under $100 anyway.

-- Kevin

[Mr.RC-CAM]

Why don't I make a really dirty, noisy powerful transmitter that sprays static and junk all across the spectrum? In no time, I would have dozens of hams helping me look for my model!
Or, you could haul a Toshiba TV on your model plane and use it as a locating device: http://www.katu.com/news/story.asp?ID=71894 :)

RC-CAM

[Cats Eyes]

OMG! I kid you not -- I read that story on... wait for it... my Toshiba Laptop! :eek:

(I guess it's a bit heavy for my Slow Stick, though...)

Thanks for sharing that!

-- Kevin

[CraigF]

Yeah, weird. I wish they had said how the TV came to be putting out that frequency at such a healthy level.

Re the GPS coords Tx/Rx: I suppose somebody with a healthy "junk box", lots of ingenuity, and with some careful shopping could do it for $100. You'd need a cheap GPS unit, an older one. They have simple displays and are fairly slow to establish lock (but fast enough after lock, so lock before flying), so are not in much demand and I've seen them for $20 and up. I am taking one apart right now...it is not meant to be taken apart (IMO to hide proprietary info since it was a consumer market "first") and it's built like a tank..I think it was ultrasonically welded shut after assembly as there are no screws or seals etc., geez it's made of some wickedly strong and thick nylon/plastic, not like modern ones. The one I'm working on is commonly available (used) for $30, has external power/ant/data cable ability. Look at the prices for individual GPS bits for experimenting, cost a lot. Hey, this may not work out or be useable, just an experiment. Oh yeah, don't forget you'd still have to have a "normal" working GPS at the user end, so you can go to those coords, and those cost around $100 up. And yes, you'd need some minimal brains at the Tx end, and likely more at the Rx end. What I'd like to do is test the concept using junk parts, to see what needs to be built, then haul out the Digi-Key catalog and try to figure out how much it would cost to do it neatly. You don't have to actually fly the prototype to test the concept. If I could get GPS coords transmitted from my junk sitting on the ground a mile away, I'd be happy. Then refine.

Anybody have any comments re the FRS transceiver idea? Before I buy some really bad ones and ruin them. I'm pretty sure most will put out the same max. legal power, so not too concerned re the Tx differences (I think??). I'm just wondering if among the cheapies some are known to have better receiving ability. If they're a type from Wal-Mart that would be handy, as we have WM in Canada and they're the best place to get electro-junk cheap (RS is the best place to get it expensive!). I could work on this on the weekend a bit. I am thinking GPS NEMA output to FSK modulate the FRS Tx carrier. If that's allowed (i.e. data on FRS band). If not, then would transmit tones, say every 30+ seconds to prevent hogging the channel.

Edit: I forgot, can't "modify" a consumer Tx in the U.S. (after all, you can't even change Tx Xtals). I don't know if that means changing the Tx RF part only, or the modulation part too...will assume the worst for now. I guess I could try the DTMF tones, "acoustically coupled", like in the old modem days, maybe even NEMA data at 300 baud...seems to work well enough (I have one of those "pocket electronic memo" things from years ago, in the days when they DTMF "dialled" the number too and not just showed it to you, and remember when PC data was stored with cassette tape tones you could hear). We're not sending much data after all, maybe 20 characters at most per message, each tone a character (DTMF) or a bit (bi-tone). I wonder if you can get a FRS radio with an external mike? So I could use the jack to input/modulate...probably not on the cheaper ones... This is getting tougher, without getting into ham stuff, and staying legal.

[windtrader]

Seems like lots of complicated ideas on getting GPS coordinates - just tape your Nextel phone on. It's the only cell provider so far that has integrated GPS functionality. Cost $0, time 0. :-)

[Mr.RC-CAM]

We're not sending much data after all, maybe 20 characters at most per message, each tone a character (DTMF) or a bit (bi-tone).
In the USA, the FRS rules prohibit non-voice communication. Only an alerting tone is allowed. Sending data, even as audio DTMF tones, would be a no-no. FWIW, the FRS channels are swamped with users in my area and are nearly useless. Range is excellent when you do get a free channel.

RC-CAM

[CraigF]

What I mean re tough for non-hams in the U.S., very strict regs. Somebody think of something. Sending the plane's coords is the obvious progression of a location device...maybe not easily doable now, but eventually. It's done commercially, but the packages are expensive and are on commercially licensed frequencies.

Many people fly where there's no cell coverage. I have read that "soon" all cell phones in the U.S. are supposed to have GPS, and even now many can be tracked anyway. Sure, put a GPS cell phone on if it'll work, I would. What I'm not clear on is if the *user* can get the GPS info from the phone, that's little talked about. It's presented as a "safety" feature, for law enforcement, anti-theft, etc.

Edit: Some flying sites not far from here are highly valued because they *don't* have cell coverage. I have heard of clubs where cell phones must be "checked at the door". Some people get spooked by them around their planes, guess they had a bad experince??

I think you could probably get away with sending a few DTMF tones, say every 5 minutes, on FRS. If you had to. Or you want to get really far out?: ASCII->speech. Then you wouldn't even need some brains at the Rx end, just a pencil and paper, or a good memory. LOL! I actually have an ASCII->speech box on my bench. It does ASCII to spoken symbol too, like the cheapie chips do but more than just numbers, though that could work too. Take that FCC!

Hey, if anybody knows of a GPS module that is very simple/modern/compact, and, say, continuosly justs puts out its location in some easily usable code, please let me know! Though I keep saying "cheap", I am willing to spend some $$$ if it really does sound usable. I just don't want to spend a lot on some module that's not meant to do what I want, since it may not work out and will just end up in my all-too-large junk box (which is essentially my whole basement).

[MX]

Hey, if anybody knows of a GPS module that is very simple/modern/compact, and, say, continuosly justs puts out its location in some easily usable code, please let me know! Though I keep saying "cheap", I am willing to spend some $$$ if it really does sound usable. I just don't want to spend a lot on some module that's not meant to do what I want, since it may not work out and will just end up in my all-too-large junk box (which is essentially my whole basement).

Look at Garmin and Trimble websites. They offer OEM modules < $75 and they only weigh from 12-14 grams. Nearly every GPS module outputs NMEA data, which is an ASCII formatted serial stream at 4800 baud, once per second.

MX

[windtrader]

Many people fly where there's no cell coverage. I have read that "soon" all cell phones in the U.S. are supposed to have GPS, and even now many can be tracked anyway. Sure, put a GPS cell phone on if it'll work, I would. What I'm not clear on is if the *user* can get the GPS info from the phone, that's little talked about. It's presented as a "safety" feature, for law enforcement, anti-theft, etc.All cell phones can be tracked to the cell that it is located but that is a far larger area than a GPS coordinate. The Nextel must make it's GPS coordinate available for commercial use since it can provide location specific information to the user's phone: "Where is the closest BigMac?" :-)

There are OEM GPS receivers that are very small, size of a postage stamp. I saw these at a show but do not recollect the additional integration components to retransmit. Some were USB enabled.

[CraigF]

OK thanks, I'll check them out. Last time I checked, about 8 months ago when I bought my last GPS (not to take apart!), there was nothing very usable unless connected to a bunch of external stuff. Besides an antenna, I got the impression they pretty much needed a computer (PDA). USB actually makes it a bit harder for me. My best receiver has USB output, puts out simple ASCII location too, besides NMEA. That's what I'd like: just continuous location output, only needs a power switch and antenna. OEM prices can be misleading I found, as they don't mention that you have to buy 1000 at least to get the advertised price. And sometimes it's the 10k price. If you only want one, they make you buy a development board, which costs a LOT.

Trimble is what I have seen used a lot in the past by experimenters. Garmin is not so easy to deal with for minor users (I've heard).

Edit: Looked around a bit, not much has changed. I can still buy a complete functioning GPS unit, very small (with screen and kb and ant. of course) and NMEA output for $100+. And a small OEM board costs 2-3 times that, with no screen and needs some brains attached, plus lots more work by me. That's why the taking apart thing (got that Magellan apart, what a job, nice-looking guts). Also, I'm curious why many of the OEM boards offer 2-5m accuracy with DGPS. That's good enough I guess, but 3m should be "normal" without DGPS, and my little handheld often shows 0.5m "accuracy" when the sats are well-positioned etc. (not that I necessarily believe it, but sometimes it says 5m or even more too). Guess it has to do with on-board processing capability, takes more and longer to keep those calcs more accurate.

I think, from a little reading, that Nextel requires you to subscribe to an extra service to use that GPS feature. Such as to their additional cost web service, and maybe more. I'm pretty sure that's where the db is kept, so it can send to your phone where that nearest McDonalds is... It's not self-contained re db (like my handheld, many pros and cons to that too). But we don't need the db, just mentioning that. Like most cell stuff, they soak you for anything but the most basic of services. Right now, I get the idea that the overall cost of their cell phone-based tracking system (what it's sold as) is not cheap and is priced for commercial users (who can write it off).

[windtrader]

craig - your research is in line with my impressions. The OEM GPS units are available but expensive. The Nextel GPS is of course an add on and geared toward commercial use. It is a lot less of an investment than what a larger transportation company woulld be willing to shell out for a location-GPS service yet let's the small operator who needs to know where his dozen trucks are about for scheduling or whatever.

The GPS path looks fairly involved and a bit costly. Just curious but how "lost" can a RC plane get? Wouldn't you be able to get close enough to get in range of one of the audio solution that would direct you to the plane? I guess it could be nearly out of sight and then you lose the signal and it goes down somewhere "out there". ET phone home!

[zl3vml]

Well, here it is at last. Very time consuming but worthwhile I think.
The top is the original circuit on vero board and the bottom circuit is surface mount components built directly on the top of the PicAxe chip with the legs snipped off.
The 5grams is for both Lithium cells.
Will fit in the model tomorrow and take another phot of the completed install.
Mark

[clipclop]

Homemade locater Tx system for rockets described here :- http://nakka-rocketry.net/frs.html uses a comercial transceiver converted + beeper driver.
Stewart

[CraigF]

Totally agree, a good loud beeper should do the job in most cases. As long as you have some idea where the plane went. It's when the plane gets away for whatever reason, and is still flying when you lose sight of it, that something a little fancier might be needed. For rocketry, the biggest problem with beepers is they end up pointing in a "bad" direction, and the sound is muffled. Probably less of a problem with a plane...I'm guessing putting the beeper near the tail of the plane would probably increase the chance it would be heard after a crash landing.

The GPS locator thing has been something I've wanted for a long time. I've been following the GPS gear progress somewhat, but I'd noticed that things hadn't changed much re OEM electronics, so hadn't thought about it again until this discussion came up. Handhelds got fancier wrt color/res, maps, speed. But there's something I've noticed, being an electronics market watcher: why are there no cheap "rip offs" by the usual suspects of GPS units made by U.S. (largely) manufacturers? I got my first GPS handheld about 10 years ago, and since then I haven't seen one knockoff. Very unusual, it seems to happen to everything else, there's something going on there, the market is tightly controlled somehow.

Also, I do not have any models that are "worth" putting hundreds of bucks worth of extra electronics in. (Well, maybe my heli, but they don't go very far on their own...) Pretty soon I *will* have one. Many people already do, and some put some pretty expensive cameras in their planes too. So I'm thinking about the GPS again.

Mr.RC-CAM mentions the FRS radios have a decent range. That still might be worth pursuing, as you can get a FRS radio with GPS built in for a reasonable price (for the Rx end). I know these GPS location systems have been built for models by hobbiests. For whatever reasons the info is held very tightly, and it almost always uses ham frequencies. I just think it's time to move past the RDF location method. Instead of transmitting a dumb tone/signal, transmit a smart one. The biggest "issue", the RF part, is pretty much the same for RDF or GPS. GPS is much easier for the user...it is not often mentioned just how much experience/practice is needed to be successful at the RDF method, it's an art and science that is not really for the casual/plugnplay user. The manufacturers do tell you this though, it's not a secret.

I do think it's pretty cool how quickly and exactly the "authorities" found that offending TV/ELT. Gear like that we could use. I imagine the people are "fairly" well trained too...

Edit: Hey, good link clipclop! So, I'm not *totally* crazy... Notice the guy's in Canada, which is less strict than the U.S. about "modding" transmitting stuff. I'm still trying to think as inclusively as possible.

[Mr.RC-CAM]

The project at nakka-rocketry.net/frs.html uses a FRS radio. For those USA/Canadian based folks that want to be remain FCC/RSS legal, please be aware that non-voice communications are not allowed on them. The rules are very specific about that.

It would be very handy if we could move the FRS's 462Mhz operation into the ham band. That could be the basis of a simple telemetry/LMA system. I've considered that solution, but it would be a bit piggish in size. So I am still hunting around for a small/cheap key fob sort of transmitter and matching receiver. Other than car alarms and remote starters, there is not much that is readily available. I am still looking.

RC-CAM

[clipclop]

UHF transmitter and receiver boards like these RC-CAM ? :- http://www.oatleyelectronics.com/remote.html
Stewart

[Mr.RC-CAM]

UHF transmitter and receiver boards like these...
I have some 433Mhz RF modules like what is shown there. But, I was hoping to find an existing consumer product that is in convenient hackable form. Even if the Tx was gutted to save weight, it would at least be functional (or nearly so) right out of the box. And having a Rx that was all dressed up would simplify construction. And it would look good too. :)

I know there are folks here that do not mind doing some serious assembly (me included). But, there are already a ton of projects like that on the net, some of which are very well documented. However, one of my goals is to try to find a way to make this simple enough for the RF impaired electronic hobbyist. This, and my other requirements, definately make it a tough nut to crack.

RC-CAM

[zl3vml]

Here is a link to some neat modules.
I "think" that 434 MHz- low power is in the industrial/experimental band but obviously that would depend on the local regulations of whichever country you are in.

http://sicom.co.nz/xurl/PageID/2214/function/viewprd/prd_id/74844/content.html

Mark

[zl3vml]

This link shows both tx & rx modules
http://sicom.co.nz/xurl/PageID/2214/function/prodlist/style/thumb/pointer/0/searchtext/343334/grpid/0/content.html

Edit: Link to the specifications of these modules.
http://www.laipac.com/easy_434_eng.htm

If you do a "Google" on tlp434 or rlp434 there are many results and pages of experiments with these modules.

Mark

[CraigF]

I'm certainly not saying to do something illegal. Trying to think of something legal that non-hams could use. I notice some of those FRS units transmit tones that have meanings (don't mean the "38 tones"), skirting the law a bit themselves. Do they mention if it has to be *human* speech? I still think if you transmitted a few seconds of DTMF tones (GPS coords as audible MF tones) every few minutes you could get away with it...it's not truly horrible, and doesn't disrupt the national communication infrastructure... I have noticed that many "voice-only frequencies" regularly have DTMF tones on them, for squelches. The good thing about DTMF tones is that they're quite easily picked out of a fair bit of noise (like somebody else's conversation... :)). I think I'll pick up one or two FRS radios (with mic jacks, seem to be common enough, even better if they have VOX) and see what they can do. I really only need one, my ham handheld can do the other end for testing, but usually only the more expensive ones are sold singly. I am curious about the range on the ground, over real terrain, don't trust range advertising in consumer radios (like watt advertising for mass-market audio gear!), too oversimplified to be meaningful. "Up to 2 miles" includes down to 500 feet, you can never be wrong when you say "up to" for something.

[Mr.RC-CAM]

FRS radios are allowed a short alerting tone which is useful for audible calling alert or coded squelch control. But, the rules specify that voice communication is all that is allowed beyond that. I do not believe the voice needs to be from a living creature, so perhaps it could be from a synthesizer. You might have to talk back to it though. :)

The Canadian RSS rules on FRS communications are very sparse. But what they do say would probably make the use of an FRS radio non-compliant for this app (it is basically telemetry rather than the intended 2-way voice).

But I agree, a couple seconds of DTMF tones, every minute or so, seems to be very innocent. It is certainly less RF invasive than some of the other projects I have come across. Just keep in mind that the FRS channels are crawling with users, so a free channel will be tough to find for some users.

A legal license-free solution is going to be tough. There are provision in the FCC and RSS rules that allowed home built devices. But they must conform to the existing rules. So, that limits the RF landscape a bit.


I am curious about the range on the ground, over real terrain...
I get about 1/2 mile in a dense neighborhood setting.

RC-CAM

[CraigF]

"I get about 1/2 mile in a dense neighborhood setting."

That is quite encouraging. A mile + in a flying environment seems very realistic then.

Being very very by-the-book legal cuts out a lot of people. And of course would put a lot of lawyers out of work. Not that we want to go there.

I don't know just how fast a DTMF tone (burst) could be sent and still be detectable cheaply. If 20 characters (DTMF tones) could be sent in 1-2s that shouldn't annoy too many people. These tones are detectable over normal conversation, so a free channel isn't necessary, but no need to be purposely inconsiderate.

Wish I could find some of those cheap ASCII/binary symbol to speech chips. Used to be really common, for making things talk (like clocks etc.). Now they seem to be integrated into the main device function. GI used to make a bunch years ago. I only need digits, or equiv. to a touch tone phone pad keys, feed the chip low impedance "speaker" output into the FRS mic jack. "More" legal, and don't need a decoder at the Rx end.

[Mr.RC-CAM]

I don't know just how fast a DTMF tone (burst) could be sent and still be detectable cheaply.
For best reliability, use (minimally) 100mS on time and 100mS interdigit pause time. This is essentially five digits per second, so full lat/long coordinates, with checksum, would probably take three seconds. Faster is possible (as short as 50ms/50ms) but reliabilty will suffer in a typical environment.


Wish I could find some of those cheap ASCII/binary symbol to speech chips.
Hmm, I sold all my spare GI SPO256 phonetic chips on eBay a couple months ago. They sat in the engineering stock for years. I have one pair left that I am saving for a rainy day. I believe that Jameco.com still has some National Digi-Talker chips in stock; they are easy to use and work very well too (very high quality speech).

The latest text to speech chip is the Winbond WTS701. It is very flexible and sounds great. But, it is not as simple to use (56 PIN TSOP).

You could also hack a talking calculator to provide speech.

I like the voice announce solutions. The human ear can easily distinguish words buried in noise and other interfering sounds. Much better than a simple DTMF or FSK/OOK method.


... so a free channel isn't necessary, but no need to be purposely inconsiderate.

It would be best to monitor the squelch circuitry. After the channel is idle for a few seconds, send the synthesized voice announcement. This will help ensure reliable communication and be considerate of the other users. And set up the broadcast so that it does not occur while in the air, otherwise it will be heard for miles and be more disturbing to the other FRS users.

RC-CAM

[CraigF]

If you just want a voice message, to transmit over FRS for RDF (to get over the technicality of "voice only"), digital recorder chips are cheap enough, make your own message. Even the Shack sells a little kit for that, speaker could be replaced by a cable to mic jack. Don't know what it sounds like, probably not great, but likely good enough. Then there's the recordable talking greeting cards etc. for even less.

There must be some common cheap hackable gadget that has an ASCII to speech, where you can still get at the binary input directly. The GI chip set I used long ago was good because it accepted RS232 input directly (wasn't the SP0256 the ROM part of it, I forget, anyway that's what I have too). A talking calculator would be fine, if we can get at the digit input part. Digital answering machine guts? ASCII input is good because less work with the GPS NMEA output.

[Mr.RC-CAM]

Even the Shack sells a little kit for that, speaker could be replaced by a cable to mic jack.
It would not work well to send GPS coordinates, but is great for fixed messages. Voice quality is so-so. I used it in this project: HamCam-ID'er Project (http://www.rc-cam.com/hamcam.htm)

The Winbond ISDcorder series could be used. The ISD parts are record/playback voice chips based on a unique non-volatile analog memory scheme. You would need to record numbers and phrases to suit the GPS application. They have addressable phrase access, so you can build up meaningful messages (string numbers together) using a host microcontroller. They are "easy" to use, but are most friendly if you have a voice recording programmer for it. A few years ago I designed a consumer product that used one of their 30 second parts; I still have the wave-file-to-ISD chip programmer for it. Quality is MUCH better than most of the stuff used in kids toys, but not fully Hi-Fi.


wasn't the SP0256 the ROM part of it
The SPO256 is the phonetic processor with ROM and the SPRO16 is the optional text-to-phonetic controller. They are used as a pair (and I still have one set of both parts for a worthy rainy day project).

RC-CAM

[CraigF]

Are you saying this isn't worthy? :) Mine are "used up" in a project. The chips are kinda big anyway.

I see what you mean re those other chips (which I've heard of, but never used), you could put each recorded number at an appropriate address, like where the ASCII code is part of the address. I suppose, any digital voice recorder chip that allows multiple messages could do that...serial addressing (probably)...more pain but easily doable if we have to have brains at the Tx end.

I have "bought" many types of FRS transceivers. I couldn't decide which one...you can help me decide, lucky guys. I notice that almost all (exept for some teensy tiny Motorola ones that some might like) are FRS/GMRS. I had never even heard of GMRS until today; as mentioned, I pay more attention to ham stuff. I don't know its legality in the U.S. There are FRS-only channels, GMRS-only channels, and some FRS-GMRS channels, at least here. On the ones where GMRS is allowed, higher output power is used. The quoted range for the most "powerful" GMRS ones I got were 5 miles and 8 miles, standard 2 miles for the FRS mode. Conditions allowing etc., one maker is honest and says the max range is *over water*. One set came with PTT headsets, though all I got have VOX capability. They all have rechargeables, some NiMH, though the ones with NiCd's seem nicer as they'll take AA (rechargeables) too. Some take AAA which I don't like, the AAA rechargeables are useless IMO. The band I work on will be as legality allows, same unit, so transferrable work. Anyway, off to get more radios, tomorrow can choose one to keep.

[Mr.RC-CAM]

I suggest you use an FRS radio that has the headset/vox feature. That way you can connect to it without any hacking and retain the legal operation. Just hack the headset, not the radio. GMRS is a licensed radio class, so it would be best to stay clear of it for this hack.

RC-CAM

[Cats Eyes]

Just curious but how "lost" can a RC plane get? Wouldn't you be able to get close enough to get in range of one of the audio solution that would direct you to the plane?
Well, I'm coming from the Aerial Photography perspective. We tend to push things to the limit, both in terms of altitude and distance, to get that shot. For instance, one gentleman lost his plane in a cloud (see Things I have learned from loosing my plane). He had no idea where it went. That was the real reason I was looking at some kind of radio solution, as the audio alarm only has so much range.

Anyway CraigF kind of answered this:
Totally agree, a good loud beeper should do the job in most cases. As long as you have some idea where the plane went. It's when the plane gets away for whatever reason, and is still flying when you lose sight of it, that something a little fancier might be needed.

* * * * *

Mark - Very nice work! Please let us know how it goes when you get it on your model.

I notice you don't have a capacitor across the PIC power pins. Perhaps you don't need it since you have fairly short wires to the battery? Also, I guess with a free-flight model you don't have to worry about either picking up or generating interference!

* * * * *


I know there are folks here that do not mind doing some serious assembly (me included). But, there are already a ton of projects like that on the net, some of which are very well documented. However, one of my goals is to try to find a way to make this simple enough for the RF impaired electronic hobbyist. This, and my other requirements, definately make it a tough nut to crack.
URL's please!!!

I'm one of those that is both "RF imparied" and do not mind doing some serious assembly. Being RF impaired does not mean I can't read a schematic or build the circuit. It would be great if you could find something simple, cheap and easy-to-build, but failing that, I'll settle for something functional, as long as it's not too expensive and doesn't break any laws.

* * * * *


Link to the specifications of these modules.
http://www.laipac.com/easy_434_eng.htm
Well, the price is right. And I can't see 8mW being illegal (don't know for sure though). Unfortunately it says range is only 500 ft. The audible alarm will do that (200 M ~= 600 ft.)

* * * * *

Can anyone point me to the Canadian Regs regarding the RF spectrum? Mr.RC-CAM keeps mentioning "RSS", whatever that is. I can't find anything like that in the "Government" section of Yahoo! Canada (http://ca.yahoo.com/).

Keep up the good work, guys!

-- Kevin

[Mr.RC-CAM]

URL's please!!!
Half the fun is digging these projects up. :) Here is one that uses low cost RF modules. Legal operation requires a ham license in the USA and Canada: http://www.birch.net/~petek/rockets/RDF/70cm.html


And I can't see 8mW being illegal (don't know for sure though).
8mW is considered sufficient RF power to cause "harmful interference." It would need to comply with FCC Part 15 (or Part 95) in the USA and RSS-210 in Canada. And in Canada, I believe that the ISM band is very limited (the 430Mhz-ish frequencies are not permitted for unlicensed operation).

There are provision for home built devices that meet FCC Part 15 and Canadian RSS-210. Just read the regs for more details. I do not believe that FCC Part 95 devices are included in this special exemption (which if true, would forbid internal hacks to FRS radios). Please be aware that the home built device must observe all the technical and operational requirements of a certified device. So, some technical RF competence is needed.


Can anyone point me to the Canadian Regs regarding the RF spectrum? ... keeps mentioning "RSS", whatever that is.
RSS is the Canadian Radio Standards Specifications. Every one of your RF products is subjected to these regulations. The Canadian Spectrum portal starts here: http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/en/Home

RC-CAM

[CraigF]

This info on (mainly) GMRS might be of interest to readers interested in RF:
http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/vwapj/sp462-467e.pdf/$FILE/sp462-467e.pdf

There's a bit of U.S. FRS/GMRS info too. GMRS sounds like CB on HF. Also sounds like *no license* needed in Canada for GMRS, for now. They were nice about ham licenses too a few years ago: no annual renewal fees. Also, licensed users of these frequencies can't complain of interference, and must move frequency...odd, because one common use appears to be medical telemetry!

I notice none of the radios I got will do 8 of the new GMRS frequencies.

Yes, the radios with mic jacks seem the best bet...they're also the most expensive. I got one real cheapie from Wal-Mart for $10...has the basic functions, but not the least-functioned I saw, FRS only.

[tve]

I haven't followed the rules very closely, but from what I remember, the US rules do not allow data (except location (gps) recently) to be transmitted over FRS. I think anything but voice communications/gps is not within the regs.

Is this wrong?

If you can tranfer data over FRS, I sure would like to know.... :) anyone?

Regards,
tve

[Mr.RC-CAM]

Also sounds like *no license* needed in Canada for GMRS, for now.
That is a good deal. I believe it is $80/year in the USA.


They were nice about ham licenses too a few years ago: no annual renewal fees.
Same in the USA. The license is valid for 10 years at a time. All you have to do is keep your address info current.


If you can tranfer data over FRS, I sure would like to know.... anyone?
No data allowed. Voice only, with the exception of a short alerting tone. A few posts up there is discussion about this.

RC-CAM

[tve]

FRS radios are allowed a short alerting tone which is useful for audible calling alert or coded squelch control. But, the rules specify that voice communication is all that is allowed beyond that. I do not believe the voice needs to be from a living creature, so perhaps it could be from a synthesizer. You might have to talk back to it though. :)
RC-CAM

Hi RC-CAM,

After your reply, I went back thru the posts and started thinking ... maybe a voice synthesizer... then I found your post :) I think it is a great idea! Another alternative might be some pre-recorded messages on one of those isd devices...

like this one:
http://rocky.digikey.com/WebLib/Windbond/Web%20Data/ISD5116%20Series.pdf

Regards,
tve

[CraigF]

Thanks for all your info about all this stuff Mr.RC-CAM.

I suspect the "no data" rule is to prevent people from totally and continuously hogging a channel...and that's what would happen if you allowed data. PTT was mentioned in that Canadian document, the spirit being *not continuous use*.

I'm leaning towards the Motorola FRS/GMRS radios ("5 mile" GMRS range, normal FRS range). They came with the remote mike. Takes AA batteries (came with NiCd AA), most take AAA's, don't last long compared to NiMH AA's. Guess it doesn't matter if you rip it apart, but JIC I use the radio (or one of them) for its intended purpose. AAA's won't last long at the GMRS power output level. Cost about US$90. I got some nicer than that, features irrelevant to the goal, but nice to have if the goal isn't attained, or for feeding my junk "box". You know, they pack all these in blister packs, so you can't try them out without making it real obvious...probably their intention, I hate blister packaging...

[CraigF]

Yikes!! Loyal readers might recall that I mentioned combo GPS/FRS radios a couple times? For use at the Rx end of my "dream" hacked GPS location system? I just checked out the Garmin ones I had in mind, and guess what: they already have the built-in capability to send the GPS location of one unit (the plane, boss) to another unit over "FRS spectrum". I wonder what method they use...will soon find out. They do GMRS too. This is it!! Not cheap though, but less than $400 for two I'm pretty sure. The last thing I need is another Garmin GPS, never mind two more, since I not long ago got a nice one, but if it does the job...

Edit: Actually, seems to be less than $300 for two, sold singly, more than one version. The plane only needs the cheapest version.

Edit again: http://www.garmin.com/products/rino/positionReport.html

There is an inference on that page that data can be sent via FRS, but not GMRS. Loophole?

[Mr.RC-CAM]

I wonder what method they use...will soon find out.
That is cool and unexpected. I just reviewed the FCC rules and all I could find was the passage about how non-voice signaling (either audible or subaudible) is allowed if it is accompanied by voice. The Garmin instructions claim that peer-to-peer location info is automatically sent every 30 secs, a limit they claim is imposed by the FCC. Even stranger is that the Garmin instructions say the unit is FCC part 15 approved (the unintentional radiator product class). But, FRS/GMRS is a Part 95 device class.

It weighs about 8 ozs, so that may limit its use to the larger e-models. But beyond that, it certainly sounds like a winner!

RC-CAM

[tve]

That is cool and unexpected. I just reviewed the FCC rules and all I could find was the passage about how non-voice signaling (either audible or subaudible) is allowed if it is accompanied by voice. The Garmin instructions claim that peer-to-peer location info is automatically sent every 30 secs, a limit they claim is imposed by the FCC. Even stranger is that the Garmin instructions say the unit is FCC part 15 approved (the unintentional radiator product class). But, FRS/GMRS is a Part 95 device class.

It weighs about 8 ozs, so that may limit its use to the larger e-models. But beyond that, it certainly sounds like a winner!

RC-CAM

They changed the rules recently to allow location information over FRS. Thats what I was referring to in my previous posts. Expensive though....

http://www.provide.net/~prsg/frs-home.htm

On February 10, 2003, the FCC released the Report and Order in WTB Docket 01-339. In that docket, the FCC had proposed to permit FRS transmission of data pertaining to the location of individual FRS units.

In the R&O, the FCC adopts changes in the FRS rules to permit such location-reporting and location-requesting communications, and to permit the transmission of other brief text messages. The transmission time may not exceed 1 second, and the time between data transmissions from a particular radio may be not less than 30 seconds (except to respond with a transmission of location information from an data query from another FRS unit).


notice the brief text message part.... (kind of implies any use...)

[tve]

This little guy is about $70 us in single qty.

http://www.royaltek.com/proditem.asp?group=oem&item=enginboard&filename=Module\rgm3000.asp&gifname=images/pg2module3000.jpg

[windtrader]

I took a look at the royaltek GPS receiver; it got me thinking about all the GPS based locator solutions being discussed and the problem with locating the receiver on the plane in such a manner it will be able to reliably lock onto the sattelites.

I know from personal experience using a Garmin handheld a fair amount in the field is you have to have a fairly clear sky view to get a decent lock. Being under trees is a problem, being down in a gulley, creek, narrow canyon, etc, is a problem. And god forbid it is facing down or sideways.

I may have missed this earlier in the thread but how have you dealt with this basic issue? Maybe you just have to go with the last know sent position before it dives in. I don't know the time between getting updated coordinates but that might not work.

Still it seems unless you can ensure the plane can land/crash in nearly any orientation and you can get a good GPS location, this option may be a lot of time and energy gone down in flames. Hope not since I am enjoying the technical aspects of all the integration.

[Mr.RC-CAM]

They changed the rules recently to allow location information over FRS.
The new rules allow for some very clever data communications. But they only allow 1 second of data every thirty seconds. But, you take what you can get.

For those of us that like to hack, this passage in the Part 95 rule text is a bummer: "Remaining in place will be the prohibition of attaching any device to an FRS radio that is not certified for use on that particular radio." That puts an end to my assumed legal workaround idea to hack the headset for connection to a voice synthesizer.


I don't know the time between getting updated coordinates but that might not work.
The new rules mention the 30-sec time between updates.

RC-CAM

[zl3vml]

Kevin,
>
>
I notice you don't have a capacitor across the PIC power pins. Perhaps you don't need it since you have fairly short wires to the battery? Also, I guess with a free-flight model you don't have to worry about either picking up or generating interference!
>
>
Yes, I have a smd cap (100n) over pin 1 & 8 which is stuck directly on the back of the PicAxe. I was concerned about the alarm possibly generating some feedback and upsetting the PicAxe but no problems experienced. Without the cap it certainly does play up though, no matter what circuit it is used in, resets, locks up that kind of thing. A cap is an absolute MUST.
The circuit has been built into my model "Stomper". When I built it (the model) I made a hatch to accomodate some kind of alarm.
Today - Sunday and it is too windy too even think of going to the airfield! Sometimes you just can't win.
Guess I'll start on my 2nd circuit. Sort of thinking of combining both PicAxe & cutdown alarm circuit into one unit which will reduce it even more....
Mark

[CraigF]

Re the hacking of a GPS locator, I don't think the ideas discussed yesterday are out the window. You could still probably "get away" with it if you stuck to being "considerate" and non-intrusive. There is still "acoustic coupling" so you might not have to physically modify what you bought. What you can "get away" with for occasional private use is very different than what you can get away with in a commercial product. So I still think sending 3s of tones or synthesized voice every minute or two is viable. If 10 million people started doing it, that could either be a problem, or more likely they'd create a new class and rules... I'm sure things in the U.S. are similar to Canada in that commercial desires cause the rule changes (notice in that Canadian document I linked to above, what they did was highly consumer-driven, almost frightenly so).

That is if you still wanted to hack something. The Rino is functionally "perfect" for what I was thinking. But the packaging is somewhat inconvenient, in that a bare module without screen and with separate antenna would be nicer/lighter. I haven't checked if you can add an external antenna to the Rino, most Garmins you can. That is important, as the Rino package probably means you'd want to mount it with the ant parallel to the ground/fuselage, and that would not be good. From the stories of hobbiest GPS locators I've read, mostly in rockets, ant position has been the downfall when poor results. There are some much better antennas now though. But if your model lands deep in some trees, any ant may not work. Then you can try your RDF skills... The position being sent every 30s is fine, that's more often than I had in mind for a hack. Notice that the way they send the GPS info is patented. So they came up with a way to send the data in a "considerate and non-intrusive" manner, then applied for a rule change...that's what I figure. That's the way it works.

As far as expensive, the places I shopped for my last GPS sell the 110 for $135-150. The Rino is easily a $50+ FRS (and GMRS) radio, and easily a $100+ GPS, so I really can't say it's a bad deal. So you need two of them, but they have to be that model. If you were thinking of a casual "normal" use GPS, and some FRS/GMRS radios, the extra cost isn't really that much. Actually, the small Garmin GPS I recently got cost more than 2 Rinos, that's the price of color (helps a lot) and flexibility with maps. And compare with an in-car nav system...Rinos are cheap!

The packaging of the Rino for our purposes isn't great, but the point is the building blocks and rule adjustments are there. The concept is workable, and not ridiculously expensive. It's even cheaper than the cheapest commercially available RDF system, plus you get some units that have some other "everyday" uses. Could be worse, better than a few years ago. Anyway, I have found this discussion interesting. I would still prefer a "stripped Rino" more purpose built for us, so I can see room for work. I don't think anything we could hack would be cheaper, but could be made more usable and reliable (re GPS reception).

Edit: You *can't* add an external GPS antenna to the Rinos. That could be a big issue. Probably don't allow it because of the transmission ability, changing the antenna could increase the effective radiated power and they don't want you to do that. We would only want it for the GPS reception antenna, but I guess the ants are integrated.

[Mr.RC-CAM]

You could still probably "get away" with it if you stuck to being "considerate" and non-intrusive.
That is probably as good as it will get with a hacked Part 95 device. It certainly could be made to observe the technical aspects of the rules and limit the non-compliance issues to the nit-pick level.

I'm still hanging on to my Part-15 compliant home built device idea. I'm still on the hunt for a worthy hackable donor.

RC-CAM

[CraigF]

^^ Actually, so am I! Partly it's the challenge. Certainly not the cost savings, in the long run. I would like something that doesn't constrain me to one manufacturer's devices and "secretive" implementation. Even if Garmin sold the Rino "module", would anything we built with it be legal, without having it FCC approved? I have many issues with the stock implementation of Rinos for model location, but I do believe it could work as the functionality is there...those who don't read the DIY forum might find it interesting.

[Cats Eyes]

Yes, I have a smd cap (100n) over pin 1 & 8 which is stuck directly on the back of the PicAxe.I took another look -- I see it now! That little brown rectangle. Not used to SMT so I didn't recognize it as a capacitor. :o


Sort of thinking of combining both PicAxe & cutdown alarm circuit into one unit which will reduce it even more....That had crossed my mind as well. The alarm circuit seems to consist of an IC (probably a microcontroller) feeding a transistor, which in turn feeds the transformer primary. No reason why we can't replace their microcontroller with our own -- have the PIC generate the tones as well as the timing and (in my case) mointoring the RX signal. Is that what you meant?

I was back at the Dollarama today and was pleased they still have loads of entry alarms -- I estimated about 200 of them. I picked up four more. At $1 each I figured I might as well stock up!

I also did some testing on the driver element. They have quite a pronounced resonance at about 3 KHz. I fed it from a variable oscillator, could hear it get quite a bit louder at the resonance. I fed it through a resistor and looked at the voltage across it on the 'scope, and it's very interesting how the waveform changes, quite quickly, as the frequency goes from the low to the high side of resonance.

Some types of piezo drivers have three terminals and are driven by an external drive circuit, which naturally drives it at its resonant frequency. In fact the Digi-Key catalog, page 1209 (http://dkc3.digikey.com/PDF/C043/1209.pdf) shows a sample circuit (at the right of the page next to where it says "Piezoelectric Ceramic Buzzer Units"). I salvaged a (three-terminal) driver element from a dead smoke alarm, hooked it up to this circuit, and it works quite well.

What I was wondering is if we could somehow make a driver circuit for our element, even though it is only a two-terminal element and we want to feed it through the transformer. The fact that it acts so differently from the high to the low side of resonance means one should be able to make a circuit that would feed it at its resonance. However, I'm at a bit of a loss as to how to go about it right now. Any ideas?

I was thinking one way to do it would be to have a PIC generate a sliding tone, and somehow "watch" the driver's behavior and see where it changes, then drive it at that frequency.

Failing that, just keep the "warbling" (i.e. sliding frequency) drive that it has now. However, it seems to me you could narrow the range considerably. The alarm itself goes from about 2.2 to 4.1 KHz. I think you could easily reduce that to, say 2.75 to 3.25 KHz and still be assured that you'd hit the resonance on each cycle. That would be a 4-fold reduction in the frequency range, so presumably it would stay within the resonance 4 times as long! That's my theory anyway. :cool:

* * * * *

Mr.RC-CAM - Thanks for the URLs. I have some reading to do. :)

The RF discussion is certainly over my head, but it looks like you guys are batting around some really good ideas and I'm sure something will emerge from it.

-- Kevin

[zl3vml]

That had crossed my mind as well. The alarm circuit seems to consist of an IC (probably a microcontroller) feeding a transistor, which in turn feeds the transformer primary. No reason why we can't replace their microcontroller with our own -- have the PIC generate the tones as well as the timing and (in my case) mointoring the RX signal. Is that what you meant?
-- Kevin

Hi Kevin,
Hmm not quite, but worth a thought. I had a closer look again and it should work if the PicAxe has enough drive and the frequency is right. Not enough space left in mine for more code though as it does the timing as well.
No, my thought was to move the resistor and cap to the bottom of the board where the chip is and stick my PicAxe to the top of the board. (above the alarm chip but on the other side of the board)

Might try that for my next one....
Yeah - I also went and bought another 10 of those alarms :D
Mark

[Ironsides]

Gentlemen:

While you pause to ponder the content of this thread, let me take this opportunity to congratulate you all on a fantastic bit of work.

While I do not understand most of it, I am following the debate and URL links with great interest.

David

[Cats Eyes]

Mark - The PIC will most likely not have enough drive current. That's the purpose of the discrete transistor in the original circuit, to increase the power handling capability. I would do it the same way -- have the PIC drive a discrete transistor to provide the signal to the transformer primary. In fact, I might be tempted to use some kind of an H-drive arrangement (push-pull) if I can find a suitable device.

The frequency would be generated in code within the PIC, so I could choose whatever frequency I want, including its progression. For instance, reproduce the sliding scale of the original circuit. Or have it play "taps" as it goes OOS. :D

Now you start to see the advantage of programming the PIC from scratch. Lots and lots of room! I can do the timing, monitor the RX signal and generate the output tones and probably only use about half the program memory space! :cool:

However, all in all, I think it would be much easier to leave the circuit as-is and just combine the two pieces as you suggest. Perhaps I'll do that for the first iteration, and see about getting fancier for version 2.0.

-- Kevin

[zl3vml]

Latest version.
I stripped the parts off the original board and cut/ground it down.
Then soldered the parts back on the side of the epoxy chip.
Glued the PicAxe chip to the empty side of the board.
Built the circuit with SMD parts onto the PicAxe chip.
All wired now down to 15grams.
I doubt I could get it any smaller or lighter than that but 15g is great!
All in all it took me about 4 hours.
Mark

[CraigF]

Just thought I'd add this addendum, since we were talking about "non-speech communication" (AKA data) over FRS/GMRS the other day. Garmin apparently "lobbied" the FCC for rule changes so that the Rino could send GPS location data in the FRS spectrum. They have done it again: the FCC recently approved text messages being sent by the Rino in the GMRS spectrum. Should have no problem getting those GPS coords out there now...

Edit: FWIW, after a LOT of digging (it's incredibly hard to get *real* radio performance opinions off the web, except from hams...), the Rinos apparently really suck as radios, pretty much like all FRS and "phony" GMRS/FRS combos. Typical range with the Rino radios is 1/4 mile in terrain where you would actually need to look for a plane. Not nearly good enough...

[windtrader]

I've been following with interest and now really understand the meaning of "hacking". That is quite some trimming, keeping circuits intact enough that everything works when amalgamated together.

Maybe I missed something over the course of this informative thread, but one of the early designs in the thread by Rc-Man was for a audio alarm triggered by an RC channel. Is this an alternate design to do the same basic functions or what's different?

[zl3vml]

WindTrader, Yes you are right, This design is for a model without radio. (Freeflight)
The Pic circuit functions as a selectable timer which then triggers the alarm module every minute after the timed period untill reset or turned off.
Mark

[Cats Eyes]

Mark - I am very impressed! Looks like quite a successful project. This is going to goad me into finishing mine! :D


windtrader - As Mark mentioned, his project is for a freeflight model. I will be making a similar one for an R/C model. The difference between mine and Mr. RC-CAM's LoMA (http://www.rc-cam.com/lma.htm) is that mine should be considerably louder, and it will be self-powered (so it will still work if the plane's power is cut off, say in a crash).

You could easily adapt the LoMA PIC to this (although I will probably program my own, as I have slightly different requirements). In fact, someone has already done this: click here (http://www.rc-cam.com/forum/index.php?showtopic=473&st=0&#entry2754).

-- Kevin

[windtrader]

Thanks for clearing this up.

Has anyone had any luck finding the cheapo personal alarms here in the States like DollarDaze, DollarClub, Dollar Store or .. ? In No. Cal. I've not had luck in the $ stores out here.

[richard tunstal]

the circuit which should be attached below
is from the book by r e kenward.

as drawn it works on 173 mhz using 57.??? xtals
which were available in hc??? cases at £1 each
(one size down from standard r/c size xtals.)

range on the ground to the cheapest scanner
i could find
is ~200yds using a 2 element
144mhz beam rx aerial and the tx probably not tuned for max
output.(last switched on ~5yrs ago!)
oh! and the lithium coin cell was down to 2.4 v.

(the coils are wound like a coil of rope)


has anyone been out with a scanner to check
the range of the rx local oscillator yet????
i know it should be minimal but until you try???
and if your toy is stuck invisibly up a tree just a few yards range may be all it takes.



one problem with audio/vis alarms is that they alert 'bad people' to
the prescence of your toy-----if you fly upwind of 'bandit country '

[richard tunstal]

i've just checked keytronics-uk.co.uk
who is still listing 57.7416 57.75833 173.225
at £1 each!

doesn't state case size though. you'd have to ask.

wonder which harmonic the 173meg xtal is on???

[Mr.RC-CAM]

...wonder which harmonic the 173meg xtal is on???
I suspect it is a fifth overtone xtal. The other two are probably third overtone.

RC-CAM

[crazy4rc]

......The module I was using was a Radiotronix RCT-433-AS. It weighs in at 1.25 grams and gets a little lighter when the connection pins are cut off short. Size is approximately 10 x 13 x 6 mm not including the connection pins. The modulation input directly keys the transmitter in what is normally refered to OOK (On-Off-Keying) and keys the entire transmitter so no power is consumed by the transmitter unless a positive signal is applied to the modulation pin.
Gail -- W5MLY
I was wondering what type of antenna you were using and how did you load it? Thanks - George

[Mr.RC-CAM]

Although this thread has been idle for the last few months, I have continued to look out for the perfect device to hack. The goal is to create a reliable RF based LMA that others could easily duplicate. That means the parts have to be readily available, require low skills to build, and be cheap.

The most promising donor devices are remote car alarms or remote starting systems. Their keyfob Tx's are tiny and the Rx's appear to have good range. However, they are too expensive for my tastes. So, at this point the only cheap solutions would be seriously DiY using Lynx's Tx & Rx RF modules or something similar.

However, if I run into the Holy Grail of hackable opportunites then I will post better news next time.

RC-CAM

[zl3vml]

Hmm yes, I need(ed) an RF tracker too.

My homebrewed audible one worked a treat. I could still hear it half an hour after I lost sight of my model disapearing from sight in a humongous thermal.

Of course, remembering to set the DT & fuel cut off timer would also have helped a bit.

However......an RF tracker would have enabled me to track and retrieve the model...

That is, if I had one and remembered to turn it on as well - in the end, there is just no excuse for stupidity! :(

Mark

[zl3vml]

Mark - I am very impressed! Looks like quite a successful project. This is going to goad me into finishing mine! :D


-- Kevin

Wow 2005 last post...

Kevin - did you ever finish this project?

I have managed to obtain a few SMD PicAxe chips so will be hacking out a new design. I have also got hold of some "muscle wire" (it shortens when you apply a small current) so am looking at incorporating a timer with a trip for DT/fuel cutoff into the new design as well.

Will post some photo's as soon as I get back onto this project.

Mark

[AndyKunz]

Tom,

Have you looked at the Keyloq devices? You can get the code under an NDA from MCHIP (I got it for a garage door project). Not exactly sure what you're trying to accomplish, but it might work for finding YOUR plane but not your buddy's :)

Andy