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Mr.RC-Cam

LoMA: World's Simplest Lost Model Alarm

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After seeing a post on eZone about a fellow that lost his expensive AP model in some thick brush, I started to think about lost model alarms again.

It is such a frustration to be close to a hiding model and not see it! There are already a couple of projects on the rc-cam.com site that include lost model alarms 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.

LoMA also includes an R/C signal glitch counter. That alone may be worth the hour's time it takes to build it. All of the juicy details are found here: http://www.rc-cam.com/lma.htm

post-7-1096004851_thumb.jpg

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Mr. RC-CAM. I was looking for Lost Model Alarms for awhile. There are several LMAs that you can buy for $15-$20. But they all miss one feature which I thought is important to have: independent battery and long life. I want an alarm that continues to work even if the main battery is discharged, or damaged in the crash. And it should continue to work for couple of days - some my previous crashes happened pretty far away. The only solution that I see is variable duty cycle generator that does 1 beep per 3-5 seconds for the first few hours and then switches to one beep in 60 seconds (or some other long period) to conserve power. The LMA can be powered by a small battery. Are you interested in modifying your LMA code to have variable duty generator option?

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I want an alarm that continues to work even if the main battery is discharged, or damaged in the crash.

The emphasis of the LoMA project was simplicity. But if you want, you can power it from an isolated 4.0 to 6.0V battery. Just disconnect the + lead from the servo cable. The rest you know what to do.;)

Are you interested in modifying your LMA code to have variable duty generator option?

Sounds good. I'll post when the software change is available.

I think it would be best if the one hour delay could be reset when the R/C Tx was turned on for a few seconds. That way you can enter an area, flick the switch, wake up the alarm to standard mode, and go hunt down the beeps. Otherwise, the one minute delay between beeps would make the search more difficult. What do you think?

Edited by Mr.RC-Cam

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I think it would be best if the one hour delay could be reset when the R/C Tx was turned on for a few seconds. That way you can enter an area, flick the switch, wake up the alarm to standard mode, and go hunt down the beeps. Otherwise, the one minute delay between beeps would make the search more difficult. What do you think?

I think that will be good. But in the actual crash I arrived to the right place too late for the receiver battery be alive - it's very easy to loose UAV model mile away from take off point :( and go searching for it for days. I don't mind having the option though.

Now I think it may be even easier to lose R/C TX connection and simplify the design. Just activate alarm one hour after power (on alarm's battery) was switched on. I was looking for something like this: Autonomous small battery, 1 hour delay from the moment power switch is turned ON, and short beeps with decreasing frequency once alarm is activated. I think that device whould have saved me many hours(!) of searching.

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It will have more universal appeal if it retains the R/C connector. Some folks aren't going to want to wait an hour and the R/C method offers good flexibility.

The new code will alert you with a series of beeps upon loss of the R/C Signal. Average current will be about 5mA using one Piezo Buzzer (two would be better).

After about an hour, it will shut off (silence). Current will be about 750uA in this state. If the Tx signal is received for a moment, the LMA will wake back up and beep again. This series of events will repeat until the battery is dead.

Is this new feature specification a good one? If not, what needs to be changed?

EDIT: Yikes, my idea won't work for a self-powered LoMA. It assumes that the R/C Rx will be working, which is not always the case.

So, I think we are back to just changing the period of the beeps after the first hour. I guess the real question is what size battery (mAH) would be attractive, and how long it needs to last. I can work out the best beep timing once the battery requirement is nailed down.

Edited by Mr.RC-Cam

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Mr. Rc-Cam;

This LoMA is briliant. Simple and functional. One thing though, I almost clipped the leads off an unburnt chip. After reading the post a time or two I jumped straight to the construction and completley forgeting to program the chip. Stupid of me but others might do the same.

Thanks for your projects. I took some time out from stuffing the MAHI board to build a LoMA. I've gone thru 5 LEDS so far on the MAHI. One on the board and the the other 4 hiding some where on my bench! That darn dot is hard to find! Oh well, the LoMA was a welcomed break.

joe

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JoeKadet, those SMT LED's are tiny. And they seem to sneak off when you're not looking. Be sure to report on your MAHI experience.

Cyber-Flyer, what battery size (mAH capacity) do you think would be practical for LoMA? I will use that to determine how to approach the buzzer timing. Keep in mind that the voltage would be 4-6VDC.

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This is totally cool!

I suspect we could just design our own battery backup circuit so if (when) the receiver battery failed, the LoMA would roll over to the backup battery and run in it's power conserving mode.

Then you could get away with using a high density non-rechargable lithium battery to maximize the time you have to search for your aircraft, since the backup battery would only be tapped in the worst case.

You'd just have to remember to unplug the backup battery before you shut down your main RC battery or the system would roll over to the backup battery... but I suppose the LoMA wouldn't let you forget ;)

Regards,

Bill

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what battery size (mAH capacity) do you think would be practical for LoMA

I am using Li-Poly rechargable 150 mAh battery with small radio beacon TX (used dog tracking collar) and it works very well:

https://www.fmadirect.com/site/fma.htm?body...Products&cat=28

I assume we can use two of them for the LMA. Or like yb2normal mentioned we can get away with non-rechargable 6v Li battery, I guess 200-400 mAh is light enough.

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Low power mode code changes are done. First hour gives ~17 beep strings per minute. After one hour you get ~7 per minute. For those that still have R/C control, cycling Tx power will restore the faster beep period. So, you get the best of both worlds. ;)

Here is what the beep string sounds like (hasn't changed from the original LoMA release): http://www.rc-cam.com/imagelma/alarm.wav

I estimate that a 150mAH battery will last 4-days. I need to do some tests to determine the exact runtime. I'll report what I find then post the new hex file if I like what I see.

As far as batteries go, you shouldn't apply more than 6VDC to LoMA. If your backup battery voltage is slightly less than the nominal R/C voltage, then simple schottkey steering diodes could be used to piggy back the backup power on top of the normal R/C voltage. If you only want to use an isolated primary battery then a 6V lithium sounds good.

The LoMA name originally was a construct of LOw parts count lost Model Alarm. Now I think it means LOw power lost Model Alarm. ;)

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Battery life has been calculated based on the measured duty cycle of the 35mA piezo buzzer. Here are the details.

Nominal PIC current is 750uA typical.

Piezo current is 7mA for the first hour (20% duty).

After one hour, the Piezo current averages 2.6mA (7.5% duty).

So, this works out to be 85mA on the first day, then 80mA per day after that. So, for three days of alarm beeps you would need a ~250mAH pack.

How does this sound?

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How does this sound? ... three days of alarm beeps ...

Oh, that's perfect. Now I have to put it on all my models ;)

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Yeah, sign me up!

I still have some of those buzzers left over from a previous RC-CAM project :)

Bill

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The new hex file has been posted. Just use the "PIC Object Code" link found in the LoMA project page.

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Rc-Cam , the PIC Object Code link returns HTTP 404 : File Not Found.

I used my LoMA yesterday. I have a habit of not turning off my receiver when I'm having fun flying. The LoMA reminds me to do that. It is hard to ignor the alarm.

Joe

Edited by joekadet

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I took it offline until I hear back from a new LoMA user. He discovered that the PIC12C509A chip did not work with the hex file. I hope to put the revised hex file online in a short bit. I'll post a note when it is ready to download.

EDIT: The revised hex file is online. Enjoy!

Using the LoMA as a reminder to turn off your Rx is a great idea. Such a simple device really delivers on the features! :)

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I've been using Radio tracking transmitter for more than two years now. Mine transmitter is made out of used RF dog collar - similar idea to bird's size tracking transmitters but mine is heavier - 1/2 oz. The problem with this technology is that range is significantly lower than you expect once the model is on the ground. That is I have no problem hearing TX from a model that is 5 miles high, but I'd be lucky if it is 500 ft when TX lay flat on the ground.

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Here is a picture of LMA combined with personal mini Alarm. I've got the alarm in the nearest pharmacy store for $4. It has batteries and piezo driver, so I thought it's a good start for LMA. I had to figure our driver circuitry and cut in with LMA PIC output to modulate the alarm own driver.

Personal Alarm's piezo driver is very loud but drows significantly higher current - up to 150mA in a peak and 30ma on average while buzzer is active. I suspect the battery will not last long but it looks cool and the removable pin is a perfect on/off switch.

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Edited by cyber-flyer

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Those little personal alarms are ear splitting! Was yours from a national drugstore chain (which one)? Can you share the specifics of the LoMA connections? Perhaps a close up photo of the wiring?

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The alarm was purchased at Walgreens. Attached is the picture of the other side of PCB. Warning it is not pretty :blink: . The signal wire from LoMA PIC is black wire on top. I had to cut copper foil on the PCB several times to reroute the power from batteries. By default the power was always applied to the circuitry and the pulloff pin was used to trigger the alarm through a transistor switch. I changed the wiring so that if the pin is pulled the power is applied, otherwise the batteries are disconnected.

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Edited by cyber-flyer

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This is a fine component. I wish I had them installed it on the last two planes I built - BOTH LOST in the brambles. :(

I've not read any comments about the effectiveness of an 85db piezo sound in the real world. I know there are many factors such as ambient noise level, terrain and vegetation type and densitiy, etc. that determine how audible the alarm will be to the bummed out pilot.

However, if one takes the time and effort to build the alarm, it seems like a louder (95-105db) would be cheap insurance. To reduce the overall current drain, it could signal less often, but a lot louder, and still be very effective in locating the plane.

Are there any inherent design reasons why a louder sound device is not specified?

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Are there any inherent design reasons why a louder sound device is not specified?

Hey, I'm all ears! :) Provide a link to a suitable buzzer and I will see if it is compatible with LoMA.

The personal body alarms are loud (up to 120dB on some). Cyber-Flyer's details the hack to use them.

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