stickyfox
Key Veteran
Location: Troy, NY, US
| I put together a fairly simple circuit that sounds a buzzer when the voltage gets too low on my CP. Now I can fly without fear of ruining the LiPo battery. It starts to whine when the voltage gets close to 9V, giving me time to land it. It's just four resistors, two transistors, and a buzzer. It cost me nothing to build, but if you had to buy everything at RS, including a soldering iron, it'd be less than 20 bucks.
Obviously, if you do something wrong and your battery, helicopter, or self explodes as a result, it's not my fault. It really is easy but you shouldn't attempt it if you've never soldered a motor on before. I'd be happy to answer any questions if anyone needs help building one.
If you're good at soldering you can fit the whole thing in no more space than the buzzer itself requires. But don't just throw it together and fly; read the instructions first because you have to calibrate it.
The circuit goes in parallel with the 4-in-1 (or whatever your receiver is). Not in series. Vout and GND represent where the radio would go. You could optionally shrink it right on to your battery, as it's cheap. But don't let it get extremely hot, as it will cause the setpoint to drift.
The transistors are 2N2222's or any NPN Si transistor you have lying around. The buzzer is a 12V piezo buzzer. Make sure that you pick a true buzzer, and not a transducer, as the latter requires a driver circuit. If there is any doubt, just connect it to a battery. If it beeps, you're in business.
If you want, you can put a hi-brightness LED in series with the buzzer for a visual warning.
Don't forget to do this! You have to pick R2 and R3 to select the point at which you want the buzzer to come on. On mine, it just happened that it beeps at exactly 9.5V, but depending on the transistors, buzzer, and whether it was Friday at the resistor factory, you will certainly have to do some experimentation to find the right crossover point. If you want it to beep at a higher voltage, make R3 bigger or R2 smaller. Do the reverse to select a lower voltage. 9V is the extreme bare not-guaranteed-to-save-the-battery-anyway minimum.
You can ignore VAm1 and VAm2; they're in there so I could check the power requirements. The whole thing uses only about 10mA when the buzzer's off, so it won't shorten battery life. You can also ignore the ground symbol; it's necessary to prevent error messages in my software.
-fox |
