Hi, I'm a bit confused about how to wire the often used NPN proximity switches.


The setup:

1x 12v Power Supply
1x 5v Power Supply
DB25-1205 chinese BOB
6-36v Proximity Sensor NPN NC


The BOB ist connected to +5v and -5v of the 5v supply. The sensors are connected with +12v and -12v of the 12v power supply.

Only the signalwires from the sensors are connected to the Pins of the BOB. The signalwires are connected with diodes to block current flow towards the BOB.


The Pins only change from 5v to ~1v if I connect the BOBs GND to both: The -12v Terminal and the -5v Terminal of the power supplies.


Since the negative Terminals aren't really GND I'm wondering if this can damage anything?


If the BOBs GND is only connected to the -5v terminal the Pins state don't change.