Could anyone help me out with a circuit to turn on an LED when the battery drops below voltage threshold? I am using this on a rc helicopter. Trying to prevent crashes.
thanks,

 

use only high value R (a few resistors) and LEDs in series-parralal branch If you need Discrete levels of voltages, No IC required

 

use only high value R (a few resistors) and LEDs in series-parralal branch If you need Discrete levels of voltages, No IC required

Interesting! I'm not visualizing it. Do you have a schematic?

Ken

 

Sounds like an interesting project. It must provide your crash indicator without significantly reducing your fly time.

You can use a low power comparator. Feed your divided down battery voltage into one terminal (+) and a reference voltage, from a zener diode or actual reference, into the other (-). Comparators like the National LMV7291 draw pretty small currents. I am not sure about which reference voltage you should use.

You will need to add some hysteresis to the comparator for stability purposes unless you don't mind the LED blinking a little while the voltages are getting close. This might actually help with power consumption.

 

You can use the 3 terminal voltage reference IC TL431 (in TO 92 package) circuit. Please refer to the following link: http://homepages.paradise.net.nz/bhabbott/lvw.html
If you can't find the IC from the electronic parts store nearby your place, get it from some on line shop such as www.epartgrocer.com.
I think the circuit can meet your requirement. Have fun!

 

That is certainly a much better solution than the one I proposed. Thanks.

 

The LM10 is low current, 8 pins and has an adjustable voltage reference (200mV and up) and an opamp that can be used as a comparator.

 

You could also look for an electronic junk shops and get cheaper electronic parts. Good luck in turning on your LED when the battery drops below voltage..

 

Here is a little Low battery circuit that has served me well over the years.

Use R1 to set the trip Voltage. At that voltage the Led should just come on.

The circuit is currently configured for a 6 volt battery. Change the zener as required.