Micro Buzzer signal lost low voltage alarm implementation discussion Ideas


[quote=“tronaton, post:80, topic:580”]
Are you powering the locator from the battery it came with?[/quote]
Yes just using a Y cable that is powering both the Loc8Tor and FPV setup (Altitude RC TTX, so built in voltage reg) from the 3.3v available at the bootloader header on the AlienWii style FC

They are not cheap but you get two tags (the TX component that fits on the quad) as well as the RX which has both LED indicators and a beeper that indicate which direction the lost quad is located in. When I stripped the case from the first TX tag I damaged the little buzzer that is attached to it so I do not have that on it and I just use the directional indicators on the RX. It is so high pitched that I can barely hear it anyway :slight_smile:


Nice diagram @pedro147 !

Nice looking build too.


This works, CUI CX-0905C buzzer (0.72 grams bare) direct drive from buzzer pin on CPU.
Buzzer current at 3.3V or less is 15mA or less, so well within max ratings of output.
Connector added for modularity and possible future changes. SH-type connector is just CA’d to controller PCB.

(I’m currently flying this in a PFG-110 frame with 8mm Medium motors from MMW. FPV is a VA2500 camera/Tx driven off of the +5V output of the controller.)

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Bravo. This has been on my todolist. Thank you for making this easier when the buzzers finally get here.


@pacer56 nice job on having the naddies to solder straight to the micro there :slight_smile:

I just bought some AWG30 Kynar wire to repair some damaged flashing pins on an Eachine H8 FC. Did you mask the adjacent pins off with kapton tape or just straight in for the kill


Thanks, just straight in for the kill on this one :sweat:. I had moral support from a friend, Etheli, who actually did this first and suggested the use of a tiny amount of liquid flux to help the solder flow better. The wire is approx. AWG38 stranded that I bought years ago from McMaster-Carr, but some similar wire is available from Hobbyking. I used a small amount of CA to tack it down after soldering so it wouldn’t get pulled up if I later had to take the doubled-sided foam tape off that is used for mounting the controller.


Smart move on the CA. I then cover mine with a bit of hot glue for stress relief.


So when buzzer goes off, what is voltage of battery when you unplug it and test with multimeter?


I’m not exactly sure what you’re asking, but here is some data I took for the CUI buzzer:

CUI CX-0905C:
Voltage, Current (mA)
1.0 , 3.1
2.0 , 9.4
3.0 , 14.7
4.0 , 19.9
5.0 , 24.8

(sound starts at slightly less than 1V)

I tested a larger one (0.37" high by 0.47" diameter) I bought off eBay and got pretty much identical results.


I guess for low voltage alarm I was asking what you have it set for and what the battery actually measures. But you might not use it that way or have it setup that way.


Sorry I misinterpreted your question.

But I have taken some of those measurements:

First, I measured the on-board resistor divider at 9.47k, 0.974k, which is a little bit off from the nominal 10k/1k.

Then I measured actual warning and low-battery thresholds at 3.65V and 3.44V with the default settings of 3.5V and 3.3V. However, this is with some custom Betaflight code developed by ETHeli that allows removing the hysteresis from the thresholds. (The ability to turn hysteresis on and off should be available soon in Betaflight.) I found that the large amount of built-in hysteresis makes setting levels particularly problematic for single-cell machines. Accuracy is also affected by the individual value of the 3.3V power supply to the CPU on the flight controller, which is also used as the reference voltage for the A/D converter.

Finally, for my setup, without hysteresis, settings of 3.2V and 3.1V worked best, using a modified version of Betaflight 2.5.4. I have found that actual voltage to the controller sags much more than people realize in these small quads. And I am using approx. AWG20 wire with JST RCY battery connectors.


And to perhaps more specifically answer the question, after landing when the warning beeps just started sounding I measured an unloaded battery voltage of 3.76V. After landing when the more-continuous minimum voltage alarm went off I measured an unloaded battery voltage of 3.68V.


Thanks. That is what I was looking for. :slight_smile:


Hey @pacer56,
Was there any additional configuration necessary to enable the buzzer? I tried mapping my aux switch for the beeper in the modes tab and the LED flashes continuously with the switch activated, but no buzzer :frowning:
Nevermind, all good now


I’m wondering how heavy these would be de-cased…
its even called an e-sky.


I ordered these a while ago. Didn’t get a chance to weight them yet.
They’re not super loud, so I don’t know how useful they would be in the field.

Note that the resonance chamber for the piezo element is embedded into the external casing. Without it, it is barely audible. You would have to carve that resonance chamber out of it to have it be useful.


i like carving.
Please let us know how this works out.
Also the de-casedvweight would be awesome.
Its suppose to run on 3v think it can handle 3.7 from a 1s?



The 3.7 from the 1s will make it louder or into a pretty smoke generator haha. I lean towards it would cope.


Louder is better.
I can follow the smoke signal to find my micro.
maybe the e-sky with a different lighter louder buzzer soldered on?


For science:
Good up to 4.2, who knows for how long though.