I have ran into a situation that requires the expertise of the Arduino hobbyists, even though this is not particularly an Arduino question. I just find these forums to be fantastic at answering questions!
So, onward we go.
I have a PLC that has inputs that are sourcing (24VDc, .5mA).
I need to detect a couple things with these inputs:
(1). That a pin is at 24VDC (it is actually wired to the same power supply that runs the PLC).
(2). That a mechanical relay has closed. When the relay is closed the wire downstream of the relay is at 24VDC (the input to the relay is connected to the same power supply.
How can I measure these 2 situations with the sourcing inputs. If i hook them directly to that which i want to monitor they simply always read 24VDC (from themselves or from the thing i am trying to measure), so I was thinking, "a transistor."
I have attached a diagram of what I think might work. If you agree that this is the right approach, any suggestions on an actual transistor that i should use?
Thanks for teaching this fool!