Indicator light circuit - frame ground

Thread Starter


Joined Oct 9, 2018
Require an indicator light to illuminate whenever a pivoting blade contacts a machine frame.
Blade is electrically isolated from the frame (a circuit wire can be connected to the blade).
Machine has a 24VDC power supply; however, a separate 12 or 24VDC supply will be used.
Circuit will operate independently of the machine’s PLC.
Circuit components:
1. Switch (metal contacts comprising a knife-blade closing on a machine frame).
2. Power supply.
3. Indicator LED.
4. Various discrete components.
In summary we need to use frame ground (not -VDC) to complete the circuit.


Joined Aug 7, 2008
Does light need to remain on for any length of time?
Power supply neg. will be frame ground even if it is dedicated supply for light.