[arvidb]

I just want to clarify the safety aspects of active high/low.

As sbrpollock says, when working with relays and other equipment requiring current to do its work, active high is the scheme to use for safety.

What makes things "safe" though is that the control circuit must be closed for the machine to do its work. In the case of a limit switch, the machine should do its work as long as the signal is inactive. And this is achieved by using a normally closed switch - then it doesn't matter if the signal is coupled as active high or active low (refer to the diagram in post #5).

For safety the pull-up or pull-down should be at the breakout board/control board, and not at the switch on the machine. It should be made so that if a cable comes loose or breaks, the resistor should still be in-circuit.

Arvid

[c_nut]

Patrick
Well said. It gets complicated the more you try to explain it. I find a schematic speaks/explains better than words.

Well my parts have arrived and I must build. I guess I am in the active high state. Sorry had to say it.
c_nut
Mile post 223 I10 in the swamps.