I've built a power supply with regulated +15v, +12v, +5v, -12v and -15v outputs and I'd like to build a voltage monitor to let me know if any of the rails are above or below their stated voltage.
I have some tri-colour RGB LEDs (common cathode), the plan is that when the rail is at the correct voltage, the LED is green, it goes red when it detects over-voltage and blue if there's under-voltage (say, ~20mV either way).
I've tried building a circuit with the LM3914 bargraph driver chip but the problem with this is it requires a common anode LED if I want to use an RGB. Also the chip is a 10 LED output and it seems wasteful to only use 3 outputs.
I've done some research and it seems like I could get something to work with op-amp comparators and either zener diodes or regulators as a reference but I don't really know enough about this yet.
Could someone please give me some advice with regards to the best way to go about this?