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Old Sep 24, 2004, 12:24 AM
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LoMA: Worlds Simplest Lost Model Alarm

After seeing eBird's All Is Lost thread, I started to think about lost model alarms again. There are a couple of projects on the rc-cam.com site that include lost model alarms as optional features. But, the LMA functions are buried in the project details and are easily overlooked.

So I thought it would be best to dedicate a project just to this function. The emphasis was to keep it simple. The result is LoMA, the world's simplest Lost Model Alarm. It has three components. Of course one is a PIC microcontroller. I hate to nag, but owning a cheap PIC programmer is really not a bad idea.

LoMA also includes an R/C signal glitch counter. That alone may be worth the hour's time it takes to build it.

All the Lost Model Alarm details are found here: http://www.rc-cam.com/lma.htm

BTW, all the rc-cam projects are summarized here: http://www.rc-cam.com/projects.htm

RC-CAM
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Old Sep 24, 2004, 01:00 AM
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Interesting project.

If you also make a hex file available for a 12F629 or 12F675 8-pin pics the project might be accessible to more hobbyists. People can get the PicKit 1 programmer for these and some 14-pin flash chips for just $36.

Just a thought.

Dowd
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Old Sep 24, 2004, 01:15 AM
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Quote:
If you also make a hex file available for a 12F629 or 12F675 ...
The project will not port over unless I make modifications. Besides, the PIC12C50x programmers sell for under $15. Parts to make one probably cost under $10. For example:
http://www.welwyn.demon.co.uk/pic_info.htm
http://talking-electronics.tripod.co...Lab-1-Kit.html
http://store.qkits.com/serv/qkits/diy/pages/QK119.asp
http://www.myke.com/elcheapo.htm
http://shopping.netsuite.com/s.nl/c....it.A/id.470/.f

RC-CAM
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Old Sep 24, 2004, 05:13 AM
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dowd,

While I don't want to hijack Mr RC-CAM's thread there is a 12F675 based LMA design here:

http://www.designsoft.com.au/ahome/rc/PIC-LMA/LMA.html

This is not 'prepackaged' you need to configure and assemble the code yourself.

Tim
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Old Sep 24, 2004, 08:01 AM
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RC-CAM, can you show what it would take to power that with a seperate battery? It would be more hassle making sure that one was charged, but it solves the common problem of the primary battery being tossed off in a crash.

Since I have field tested LMA's before and found them to be challanged in noisy settings, I was wondering about putting two buzzers back to back for a better chance that it will be pointing in your general direction rather than away from you. Also, leaves and stuff can muffle them so this gives you two chances at unobstructed sound.
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Old Sep 24, 2004, 09:19 AM
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This is a good start, but we are really going to have to find a louder buzzer. I briefly lost my SS in a bean field a couple of weeks ago. It had a home-brew LMA on it which was essentailly the same as yours, a PIC powering a peizo buzzer from Digi-Key. Mine is rated at 90dB. It was about 100' out in the field, and even knowing where it was, I couldn't hear it over the crickets and other ambient noise. I didn't hear it until I was about 20' from the plane!

I don't mean to denigrate your efforts, and I hope this will lead to a product that will truly be effective. But IMHO as it is, it will just give you a false sense of security. What we need is something very loud, much louder than these little PCB-mount buzzers.

My 2 cents.

-- Kevin
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Old Sep 24, 2004, 11:01 AM
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Quote:
While I don't want to hijack Mr RC-CAM's thread there is a 12F675 based LMA design here...
That is a great looking project. Nice job TugBoat.


Quote:
... can you show what it would take to power that with a seperate battery?
External power can be applied by isolating the + power connection from the servo connector. Only R/C Sig and gnd will go to the Rx. Connect your 4VDC-6VDC battery source to the PIC.


Quote:
I was wondering about putting two buzzers back to back for a better chance that it will be pointing in your general direction rather than away from you. Also, leaves and stuff can muffle them so this gives you two chances at unobstructed sound.
LoMa has enough drive current to power two of the piezo buzzers specified in the project.


Quote:
This is a good start, but we are really going to have to find a louder buzzer.
For more extensive audio coverage, it would probably be more effective to mount two or three transducers at different locations on the model (rather than one big one).


Quote:
... But IMHO as it is, it will just give you a false sense of security.
Frankly, using an LMA of some kind is better than nothing at all. Beeping gadgets like these have been effective for others in locating lost models. But, they are not perfect.


Quote:
What we need is something very loud, much louder than these little PCB-mount buzzers.
Those personal jogger alarms and the HobbyZone Combat module are a bit louder. They would be good targets for an LMA hack. In my case, I was looking for something that would be VERY simple to build, tiny/lightweight, and very low cost. Hence, LoMA was created. Anyone that can solder could build this thing.

RC-CAM
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Old Sep 24, 2004, 11:12 AM
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ok 90 dB is not really loud I agree.. it's about as loud as a lawnmower
I thikn something in the 110-120 db range would be sufficient, however you would need earmuphs as you get close to the plane.

-allenkll
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Old Sep 24, 2004, 02:03 PM
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RC-CAM,
Did you try driving the buzzer differentially instead of single ended? If the PIC will stand up to it you could effectively double the voltage being delivered to the peizo element and increase its output level. From your schematic you appeared to have one free pin. Instead of driving one end of the speaker with 3 pins in parallel you could perhaps use 2 pair of pins on each lead and run them 180 deg. out of phase.
Also a lot of inexpensive peizzo speakers have a hot spot in their freq vs. output level characteristics so if you were to drive it a few hundred hertz off from the peak it might not be as loud as it could be.
Third thought would be if you can drive the speaker differentially then you could play with duty cycles and search for a combination that produces harmonics that may deliver more usable output of the speaker. Remember the circuit model of a peizo (speaker) includes both capacitive and inductive elements so if you can find the resonances in the circuit you may get some "free" amplitude peaks if you get the right harmonic. Bad news is it might vary from speaker to speaker so you would really need to try it out and do a pick the best average type thingy.
Just some off the cuff thoughts.
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Old Sep 24, 2004, 02:34 PM
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Quote:
Did you try driving the buzzer differentially instead of single ended?
The Piezo Buzzer I use has the osc drive circuity in it. So differential excitation does not apply. It's native frequency is set by the mfg, but I pulse it to make it easier to distinguish the tones above the background noise. See the attachment for a sample audio clip.

The spare pin is really not spare. It is an easter egg of sorts. It is a "TTL" level output that can be used to drive a buffer transistor for those apps that need more alarm buzzer current or want to flash Hi-Lumen LED's. Don't tell anyone it is there.

You are correct about the resonance of raw piezo transducers. If you don't drive them at the correct frequency they lose a lot of efficiency. Some become mutes.

RC-CAM

Edit: The attached Zip file does not seem to work right. Here is an alternate link for the audio file (must do a right-click, save-as): http://www.rc-cam.com/imagelma/alarm.wav
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Old Sep 25, 2004, 09:57 AM
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Hey,

I have looked into the buzzers for this project before, and 110db is not attainable unless the buzzer is quite large in physical size, too large for a plane anyway. I don't know how we can make it lound enough to actually hear well and maintain a small size.



-Matt
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Old Sep 25, 2004, 11:08 AM
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Quote:
Originally Posted by Mr.RC-CAM
Frankly, using an LMA of some kind is better than nothing at all. Beeping gadgets like these have been effective for others in locating lost models. But, they are not perfect.
Okay, I agree that having a buzzer like this is better than nothing. I was rather disappointed in the LMA on my plane, but I guess I was hoping that I could just stand by the edge of a field and hear it. That frustration, and feeling Steve's frustration as well, may have made me a bit too quick to criticize. Sorry.

If your plane comes down in a field without any kind of LMA, it is possible that it ends up covered with leaves, stuck in a tree or otherwise not visible. You can criss-cross the field 'til the cows come home and never find it, even though you may have passed within a few feet of it on several occasions. With your LMA, if you manage to get within 20' or so of your plane, you will likely hear it.

However, there are other situations where you would need something much louder. If you don't know exactly where your plane came down (it's hard to judge distance sometimes), it's possible that the plane isn't even in the area you are searching. In very dense forest or swamp (such as Steve is faced with), it would be very useful to know beforehand the exact location of your plane, to save you having to hack your way through the whole area.

I think as long as people recognize its limitations and what situations it will be useful in, this is a good project. As you say, it's very simple and can be put together quickly by anyone with a soldering iron and a PIC programmer. I for one would not have thought of soldering the PIC directly to the buzzer. Brilliant -- saves space and the weight of a PCB board. So I will quit criticizing and get to work building a louder LMA.

Thanks for your suggestions about the jogger alarm and Combat module. If the buzzer I'm looking at doesn't work out, I'll look into those.

-- Kevin
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Old Sep 25, 2004, 11:20 AM
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I have another suugestion to make on a LMA as long as people are designing them. How about one that combines a buzzer with a high output LED. If you can't hear the buzzer at the edge of the field, you might be able to see a blinking LED if its dark out and there's no other bright lights around. People's eyes get very sensitive to light once you've been outside for a while.
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Old Sep 25, 2004, 11:44 AM
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LED's could help, but would require the battery supply to last until nightfall. And I agree, louder will mean bigger. So, for an LMA to be attractive it will need to be a balance of performance vs. weight/size/cost. But like all safety devices, perfection may be difficult to achieve, especially at low cost.

I wonder what the outcome of eBird's situation would have been if he had an audio based LMA on his model? Even with its limitations, perhaps it would have helped locate the model. Or maybe not. We will never know.

RC-CAM
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Old Sep 25, 2004, 12:02 PM
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How about one with RF tracking and Buzzer?
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