This simple board permits to combine two 12V power supplies to a single output while keeping status monitoring using LEDs, and having a power switch allowing to isolate a power block for replacement without powering everything down. The schematic is very simple:
For each power input, the LED will indicate one of these states:
- all down (off)
- this PSU is unconnected or dead (red)
- this PSU is connected but not enabled, no output (blue)
- this PSU is connected but not enabled, output from other PSU (purple)
- this PSU is connected and enabled but diode is dead (cyan)
- this PSU is not connected and diode is short-circuited (orange)
- this PSU is connected and delivering power (green)
The entire project is described here, and this repository simply contains the necessary files to duplicate the board. They were made using Eagle 7.7 though most other CAD software should be able to reuse them. The power diodes are 20SQ045 by the way.