How do I design a circuit for a bi-color led to display power?
A resistor, R4, is used to pulldown VLOAD when  the SPST switch, SW1, is open. This means that when SW1 is closed, VLOAD is high, and when SW1 is open, VLOAD is low.

An NPN digital logic inverter is used to provide the complement of the VLOAD signal. The input to the inverter is VLOAD, and it is powered by the voltage source. The output of the inverter is VLOADN.

D1 and D2 have shared cathodes. Since VLOADN = ~VLOAD, there is always one LED that is on while the other is off:


If SW1 is closed, the inverter input is high. D1 is on and D2 is off.
If SW1 is open, R4 pulls the input of the inverter low. D1 is off and D2 is on.








simulate this circuit &ndash; Schematic created using CircuitLab