Unfortunately I am new to the hardware side of things so my question is really basic.
Basically I need to monitor 6 separate 12v automotive circuits for the presence of ground (they are fed into the vehicles body control module). Can I tap the these lines directly into the pins of my Arduino and then define them as a pullup input?
You want to see if they go low? They normally sit at 12V?
You could have the signals drive an optcoupler, when they are high they can have the open collector outputs pull an input with pullup resistor low. When the signal is low, the open collector output will not be low and the pullup resistor will read high.
Sorry - to clarify
they normally sit open, and go to ground when closed.
what I am thinking is that the pullup will show high until the circuit closes - then it will go low
Okay, connect to base on NPN transistor, with pullup to +12.
NPN will be on, connect collecter to Arduino, emitter to Gnd - chassis & Arduino.
When circuit goes low, NPN will turn off & collector will go to Arduino level high from the internal pullup.
If the levels sit at 12V when "open", this will isolate the arduino from 12-14.5V that will likely occur on the lines.
If the levels are not connected to anything, and just float, then you'd be sage connecting to an input directly with the internal pullup.
excellent, that was what i thought, the lines switch between ground(-) and float.
the fast help is much appreciated 