I am looking for a circuit to monitor a digital voltage level.
If the voltage is below a certain level, it will light an LED.
If the voltage is above a certain level, it will light another LED.

We are looking for the very simplest form of this circuit.
A circuit of combinatorial logic with the fewest parts.
Everything that we are finding is large in size.

Does anyone have any idea's as a solution ?

 

Hi annapolis

The below circuit ought to do the trick. Any old comparator should do the trick, but 311's should still be around. Set the trim pot to the level where the voltage change is critical.

 

hi

here's another set-up you can look into

 

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.