DIY Crash Alarm

[mike240se]

Hi all, I am looking to make a crash alarm for my planes which run off spektrum dx-7 but i am looking to do it different than the ones on the market, they all sense loss of signal, low battery, go into failsafe, etc and i dont want all this extra junk that makes the plane beep all the time and made my friends throttle go crazy on a low battery. Plus i dont want to waste $20 for something that i think i can make myself from radioshack...

I just want to make a beeper with a tiny speaker that goes off when i turn on a channel, thats it. No extra junk.

I am also looking to make a simple switch, basiclly, i flip a channel the switch closes two wires and vice versa. This is for a light system to turn on in air.

thanks.

[mike240se]

anyone?

[orraman]

I have been told that Spectrum can use standard servos so a servo amplifier with a diode and a dc sounder in place of the motor might suffice.

Dave

[Bearded Flyer]

Try this http://www.uoguelph.ca/~antoon/gadgets/rc-sw.htm or other circuits on the same site.

Richard

[mike240se]

I have been told that Spectrum can use standard servos so a servo amplifier with a diode and a dc sounder in place of the motor might suffice.

Dave


interesting, i took a servo amplifier out of a busted eflight s75 servo but cant figure out how to get it to work. it has a yellow, red, black coming out and going to something inside the servo, the red and black give me 4.5v but the yellow and black give me nothing, and then a red, blue and black going to what looks like a motor. the red and black give me 4.5v (or maybe it was 2.5) and the blue and black give me .8v. i tried hooking it up to the gear switch but they all read the same no matter if i switch the gear or not. also i think the little amplifier was getting hot after having it hooked up for a while (with the motor cut off)

can you please elaborate on your above idea? thanks!

[orraman]

I have no first hand knowledge of that servo but from it's specification it appears similar to this one.

In this photo the output shaft extends upward to turn the wiper (centre of the three connections to the amplifier) in the potentiometer ("variable resistance"). The proportions of the resistance above and below the wiper 'tell' the amplifier in which polarity (direction) to power the motor to follow the transmitter. With the wiper centered on this servo the measured resistance is 2800 ohms each side so the potentiometer could be replaced with two resistors near this value. You only want power in one direction and a diode does this.

Two poor photos show one motor lead connected to a 'fairy' bulb in series with a 1N4001 diode to the other motor terminal with the transmitter gear switch on and off. The current was 100mA and the amplifier only slightly warm so the health of your amplifier is questionable. Depending on the power taken by the sounder it may be prudent to flip the switch in short bursts.

Dave

[MarkusN]

it has a yellow, red, black coming out and going to something inside the servo, the red and black give me 4.5v but the yellow and black give me nothing This is the cable coming from the Rx, right? Black is GND, red is power, yellow is signal.

and then a red, blue and black going to what looks like a motor. the red and black give me 4.5v (or maybe it was 2.5) and the blue and black give me .8v.I assume that what "looks like a motor" is actually the potentiometer; no reason for a servo motor to have three connections. (I very much doubt that the motor is brushless...) Again black and red are GND and power, Blue is the wiper. As Dave said: replace the pot by two fixed resistors of similar value. Then go find the output that goes to the actual Motor (the motor is directly soldered to the PCB on many current designs) and connect the buzzer and a diode in series there.

[mike240se]

This is the cable coming from the Rx, right? Black is GND, red is power, yellow is signal.

I assume that what "looks like a motor" is actually the potentiometer; no reason for a servo motor to have three connections. (I very much doubt that the motor is brushless...) Again black and red are GND and power, Blue is the wiper. As Dave said: replace the pot by two fixed resistors of similar value. Then go find the output that goes to the actual Motor (the motor is directly soldered to the PCB on many current designs) and connect the buzzer and a diode in series there.

No, not the rx wire, these wires are all attached to the amplifier.

The pot has a yellow, red and black going to it. yellow is attached to the plate thing in the middle.

The motor def. has 3 wires going in, blue, red and black. As far as i can tell red and black are 4.5v+ dc and blue and black are .8v+ DC. I dont think its brushless cause i dont see how such a tiny board could convert to ac power, but maybe it can. If its brushless that may explain why i have never seen a negative voltage.

[mike240se]

I have no first hand knowledge of that servo but from it's specification it appears similar to this one.

In this photo the output shaft extends upward to turn the wiper (centre of the three connections to the amplifier) in the potentiometer ("variable resistance"). The proportions of the resistance above and below the wiper 'tell' the amplifier in which polarity (direction) to power the motor to follow the transmitter. With the wiper centered on this servo the measured resistance is 2800 ohms each side so the potentiometer could be replaced with two resistors near this value. You only want power in one direction and a diode does this.

Two poor photos show one motor lead connected to a 'fairy' bulb in series with a 1N4001 diode to the other motor terminal with the transmitter gear switch on and off. The current was 100mA and the amplifier only slightly warm so the health of your amplifier is questionable. Depending on the power taken by the sounder it may be prudent to flip the switch in short bursts.

Dave


dave thanks alot for the pictures and info, after rereading your post i am starting to understand. I realiz now what the diode is for. Besides my problems in the above post, i have a few questions.

I understand that you need to put a resister where the pot was to tell the amplifier the servo is centered but if its centered wouldnt it not send any signal to the motor? Also you mention two resistors, 2800ohms each, is one from the wiper(yellow) to red(pos) and the other from the wiper (yellow) to ground?

Now the DC sounder, i assume its going to get 4.8v, the voltage of my bec/pack?

Any ideas about my motor with the 3 wires?

thanks

mike

[dusty IV]

Seems like when my planes crash the battery gets tossed and unplugs everything. I have also found the piezoelectric alarms available are not very loud. I suppose better then nothing. I made up a parabolic amplifier once to detect it. Never found a plane with it.

I just bought a tracking device, Loc8tor. The reviews are to good to believe but I will see. 2.4G RF chip on the plane that a separate xmitter turns on. The hand held device has a screen that points to the plane. 600' range. Cost from Sharper Image about $170 + s/h. I got it off e-bay for $100 delivered.

I decided a lost plane is a very expensive deal and the $100 is well spent if it works. I hope it works as claimed. Sounds like every club should own one. 24 different chips available.

[MarkusN]

Sorry if I sounded patronising before; it's sometimes difficult to assess how much technical knowledge an inquirer has.

I understand that you need to put a resister where the pot was to tell the amplifier the servo is centered but if its centered wouldnt it not send any signal to the motor? Also you mention two resistors, 2800ohms each, is one from the wiper(yellow) to red(pos) and the other from the wiper (yellow) to ground?Right for the resistor setup. And if the Servo 'felt' precisely centered it would indeed send no voltage to the motor. But when you activate the alarm with a switch, you are asking the Servo amplifier for an off-center position; so the motor would be powerd up.
BTW, you can also use a standard trim pot to replace the servo pot and precisely adjust it for zero. Not that it matters for this application, but it might in another.

Now the DC sounder, i assume its going to get 4.8v, the voltage of my bec/pack? Yep.

Any ideas about my motor with the 3 wires? Not really. The colors don't sound right for it being brushless. You would avoid having the standard DC black and red there (at least I would.) There sometimes is protection cirqcuitry (capacitors conncted to motors that also connect the body of the motor. Might be this. Could also be that it's some kind of Sensor.
Have you tried moving the pot and if that changes any of the voltages to the motor? What is shot on this servo, anyway?[/QUOTE]

[orraman]

Mike,

From searching the web the s75 is advertised as having a coreless motor which is normally a brushed DC motor that has less iron in the rotor.

Here is a quick picture of an E-sky EK2-0500 which has similar specifications and club ended output arm (coincidence?) to your s75.
Just discernable between the red and blue wires going to the motor is the end of a third (black) wire soldered to the motor casing and I assume that it is for suppression.

A potentiometer acts as a potential divider with the wiper picking off a potential (voltage) that is proportional to the resistance above and below the wiper. The wiper turns with the output shaft and the voltage from it is the error signal between where the output arm IS and where the transmitter WANTS it to be and the amplifier drives the motor and the wiper to reduce the error. We don't want the motor, it is the amplified error signal that we want to drive the sounder. If the wiper is in the centre then left on the transmitter will give full left (perhaps negative?) error power but this is the side we have blocked with the diode, full right will pass power through the diode and the sounder just like the fairy lamp.

Replacing the potentiometer with resistors is mainly to save space but if you want to use a 4 channel transmitter for a 3 channel model then retaining the 'pot' allows you to choose the operating point and move the trim to one side and maintain silence with the stick at the centre. With the wiper slightly to one side and the trim set over the fairy light is now working reliably on channel 4.

There is always a voltage drop over a diode, 0.6V on the one I used, there are also losses in the amplifier so I have 3.4V measured over the lamp. However the amplifier is not short of 'power', perhaps 500 mA at 3.4V gives 1.7W, well up on small radios volume so it would be a matter of seeking a matching sounder.

dust IV,

Please keep us informed of your results with your Loc8tor.

MarkusN,

Please excuse me for elaborating on points you have just covered but I write exceeding slow and you posted just before I finished.

Dave

[mike240se]

Dave thanks so much for explaining it so well an in such detail, its a great help. I understand much better now.

I bought everything i need today, diodes, resistors (2200 ohm and 3300 ohm, they didnt have 2800) and some piezo buzzers. The buzzers are quite lackluster though, you cant really hear them and a beeper would work so much better. I guess radioshack doesnt sell beepers? A DC Sounder would be a beeper correct? I guess i will have to order one online.

I realize now that the red and blue are for the motor and the black is grounded to the outside of the motor just as you said mark. I am going to start testing everything with my meter, which has been a pain with the standard probes, i have to find something better.

I will post more after my initial trys. thanks!

mike

[mike240se]

hey it worked great! Well it worked great but not really :) the piezo buzzers at radioshack are crap, i need somrething theat beeps.

i also want to do a better design, i want it to have its own power source and have the ability to turn on if it loses signal, but that is gonna be a problem with spektrum, it has failsafe which wont turn off the signal. i will have to find away around that.

[orraman]

Mike,
Good to know that you have something working. I tried to get the sounder used in the microscream, Rapid are out of stock but the one they sent is rather feeble. I ordered a submin 5V relay which works down to 3V and this works well in place of the sounder and for this you could use the smaller 1N148 signal diode to replace 1N4001. This should allow you to use any sounder, perhaps a personal attack alarm with it's own battery. It measures 3/8" x 1/2", an alternative will be available in the US.
http://www.rapidonline.com/searchresults.aspx?style=0&kw=60-0680

A world of information in these threads
http://www.rcgroups.com/forums/showthread.php?t=221018&highlight=screamer
Here an FET is used to drive the sounder from a higher voltage.

http://www.rcgroups.com/forums/showthread.php?t=278905

For your Spectrum it should be fairly simple to monitor two servo outputs with a microcontroller, testing a stick position for alarm on command and time since last change in signal on the throttle. More 'interesting' to do it from a single output.

In small numbers Picaxe are the cheapest micros considering that no programmer is needed. P H Anderson sells the 8 pin 08M chip at about $10.99 for three and if you are not yet into Basic programming the free editor can download directly from the built in Flow Chart. This chip holds about 80 lines of Basic code, quite enough for what you require.
http://www.phanderson.com/picaxe/picaxe_overview.html
http://cgi.ebay.com/BASIC-PICAXE-08M-3-Smaller-than-a-postage-Stamp_W0QQitemZ140150578853QQihZ004QQcategoryZ4661 QQcmdZViewItem

My latest "all singing, all dancing" surface mount board is detailed at the bottom of this thread and you are welcome to one of the bare boards if you care to go that way.
http://www.rcgroups.com/forums/showthread.php?t=741545
However the normal DIL 08M would need a piece of stripboard about 6 holes by 10 with a relay or driver circuit taking the place of the servo pins in this photo, assuming a remote sounder. Standard parts are more readily available and size would not be much greater, perhaps 5/8" x 1".

A simplistic Basic programme to monitor one servo channel and sound an alarm might manage on 3 lines of code and a label so I could try to help there.

Dave

[mike240se]

Mike,
Good to know that you have something working. I tried to get the sounder used in the microscream, Rapid are out of stock but the one they sent is rather feeble. I ordered a submin 5V relay which works down to 3V and this works well in place of the sounder and for this you could use the smaller 1N148 signal diode to replace 1N4001. This should allow you to use any sounder, perhaps a personal attack alarm with it's own battery. It measures 3/8" x 1/2", an alternative will be available in the US.
http://www.rapidonline.com/searchresults.aspx?style=0&kw=60-0680

A world of information in these threads
http://www.rcgroups.com/forums/showthread.php?t=221018&highlight=screamer
Here an FET is used to drive the sounder from a higher voltage.

http://www.rcgroups.com/forums/showthread.php?t=278905

For your Spectrum it should be fairly simple to monitor two servo outputs with a microcontroller, testing a stick position for alarm on command and time since last change in signal on the throttle. More 'interesting' to do it from a single output.

In small numbers Picaxe are the cheapest micros considering that no programmer is needed. P H Anderson sells the 8 pin 08M chip at about $10.99 for three and if you are not yet into Basic programming the free editor can download directly from the built in Flow Chart. This chip holds about 80 lines of Basic code, quite enough for what you require.
http://www.phanderson.com/picaxe/picaxe_overview.html
http://cgi.ebay.com/BASIC-PICAXE-08M-3-Smaller-than-a-postage-Stamp_W0QQitemZ140150578853QQihZ004QQcategoryZ4661 QQcmdZViewItem

My latest "all singing, all dancing" surface mount board is detailed at the bottom of this thread and you are welcome to one of the bare boards if you care to go that way.
http://www.rcgroups.com/forums/showthread.php?t=741545
However the normal DIL 08M would need a piece of stripboard about 6 holes by 10 with a relay or driver circuit taking the place of the servo pins in this photo, assuming a remote sounder. Standard parts are more readily available and size would not be much greater, perhaps 5/8" x 1".

A simplistic Basic programme to monitor one servo channel and sound an alarm might manage on 3 lines of code and a label so I could try to help there.

Dave

wow! thanks dave, this is gonna give me lots to do this winter. this basic chip looks like fun! i used to be awesome at QBASIC when i was a kid, is it like non-ms BASIC or is like totally different? If its regular computer BASIc then i might pick it back up quick.

I was going to order that from the ebay auction you posted but dont i need the starter kit with the programming cable?

http://194.201.138.187/epages/Store.storefront/?ObjectPath=/Shops/Store.TechSupplies/Products/AXE003


like that one? but maybe you know of one in the US? that auction store didnt have anything but chips by themselves.

[orraman]

The link you posted is the dedicated sales site for Picaxe and while the prices are fair the postage is not, particularly to the US so I have read.

http://www.rev-ed.co.uk/picaxe/ is the home page where you can download the free editor which contains a helpful introduction and the technical help button leads to a very active forum.
The download cable with the 3.5mm stereo plug is very convenient when used with the very convenient small printed circuit prototype boards but the stereo socket is not so convenient (hole spacing) for DIY boards.
A 9 pin serial socket is the cheapest download and there are 8 pin kits and solderless breadboards here, wish we had such a UK supplier, single 08m on UK ebay for £4.49.
http://www.phanderson.com/picaxe/

My development board is here, I prefer to keep it all mobile and use batteries, the whole set-up is in the picture and you are welcome to a bare board.
http://www.rcgroups.com/forums/showthread.php?t=727280

I use a tiny sub-set of the of the very comprehensive Basic which is centered on control with a slant towards RC. The book is helpful, some drawings are wrong but still well worth while.

Your original requirement works fine in three lines.

Dave

'Prog to monitor GPIO3 for positive pulse
'Alarm on GPIO2 right stick ch4 Futaba

start:
pulsin 3,1,b2
if b2 < 170 then start
high 2

[mike240se]

The link you posted is the dedicated sales site for Picaxe and while the prices are fair the postage is not, particularly to the US so I have read.

http://www.rev-ed.co.uk/picaxe/ is the home page where you can download the free editor which contains a helpful introduction and the technical help button leads to a very active forum.
The download cable with the 3.5mm stereo plug is very convenient when used with the very convenient small printed circuit prototype boards but the stereo socket is not so convenient (hole spacing) for DIY boards.
A 9 pin serial socket is the cheapest download and there are 8 pin kits and solderless breadboards here, wish we had such a UK supplier, single 08m on UK ebay for £4.49.
http://www.phanderson.com/picaxe/

My development board is here, I prefer to keep it all mobile and use batteries, the whole set-up is in the picture and you are welcome to a bare board.
http://www.rcgroups.com/forums/showthread.php?t=727280

I use a tiny sub-set of the of the very comprehensive Basic which is centered on control with a slant towards RC. The book is helpful, some drawings are wrong but still well worth while.

Your original requirement works fine in three lines.

Dave

'Prog to monitor GPIO3 for positive pulse
'Alarm on GPIO2 right stick ch4 Futaba

start:
pulsin 3,1,b2
if b2 < 170 then start
high 2

that site is great, i am going to get the book and the 8 dev package with the breadboard and serial etc. but what does one do when they want to make it small enough for a small plane? is that board that is attached to your bread board the board you are refering to? how does it work without the breadboard though? it appears it needs the breadboard for power. obviously i cant put a breadboard in my plane, even their prototype board is WAY too big for a plane. is there a way to put everything on that miniboard?

what do you mean i am welcome to a bare board? you sell them?

[orraman]

Solderless development boards have strips of spring contacts that make it easy to change components but can be strained if 0.1" RC type square pins are inserted.
Protoboards use more secure soldered connections and with careful use of desoldering braid can last for many changes.
When satisfied with your design you can replicate it on a small section of normal prototype board from Radio Shack or ebay.

My 'Sideboard' is intended to be a modular micro with download. Once the circuit is developed and transferred to protoboard the sideboard can be soldered or plugged in.
A 0.1uF suppression capacitor is always advisable across the power pins of a pic and to download programmes the Picaxe requires 2 resistors to keep the PC rs232 voltage off the input pins. Sockets for the Picaxe and the download wires and pin/sockets taken from IC sockets to make a self contained unit.

The board is single sided with the legs of the socket cropped and the sides shaved to ease soldering. There is room for normal resistors and capacitor but I have used surface mount because it's easier, no drilling.

The photo shows a normal programming session, battery powers the receiver (silver foil), to the board, Picaxe, the LED (to simulate output). Download cable remains attached, a debug instruction within the programme can send the programme variables to the PC as they change. Alterations to the programme are made on the PC and the original programme continues to execute until the download button is clicked when execution is halted for a few seconds then restarts with the altered programme. I needed to add a fourth line to the previous programme and this was done on the setup shown and reads "low 1".

I needed to complete the circuit from GPIO2 to ground but the supply negative goes to the only ground socket. With this extra instruction power flows from GPIO2 through the resistor, the LED and 'sinks' through GPIO1 to ground.

At 5/8" X 7/8" the board should be suitable for model aircraft, the 3 download sockets are needed but the front row of holes could provide good anchorage for servo leads etc. I would suggest that you could programme Picaxe chips on this board and transfer them to scraps of protoboard without bothering with download components but tying the input pin to ground, perhaps via a 10k resistor to prevent spurious signals being seen as download. In this way you could tailor the protoboard to your output requirements, remembering that the Picaxe has almost unlimited downloads and protoboards are relatively inexpensive.

I have a couple of these boards spare so you could refund postage if you wish if you PM me your address.

Dave

[dusty IV]

I just recently bought a Loc8tor for about $100 delivered off Ebay. It uses a 1/4oz rf chip mounted on the airplane.A separate hand held 2.4 xmitter turns it on. The hand held unit talks to the chip back and forth.

A LCD display points to the airplane/chip. Range that I checked appears to be about a 100'. I don't know what it is in the trees.

Looks like it may work . I have to test more.

The manufacture is coming out with a cheaper version with out the LCD display.

[orraman]

dusty IV,

Thank you for the update. Somewhat disappointing about the range considering what is advertised but how many times has a modeller passed within 100' of his model when searching? Another point, when walking, the search is being done 100' left AND 100' right.
Surprisingly, on searching I find Loc8tor available in the UK for £60, about $120 and a cheaper unit would be good.

On the aerial photography forum a model was found from the picture being transmitted by a 0.5oz (15gms) security camera that was being used as a downlink. On the same forum someone hacked a 10mW transmitter from such a camera, it weighed about 2gms and some cameras of this type have audio transmission. At the time I thought of the possibility for an alarm and 200mW units are available.

Dave