PMDX 126 limits/pogo

[courter]

I am planning to try some spring pins (pogo pins) for my XYZ home switches. Can the machine frame be used as a negative conductor for a spring pin connected to the 126 input terminals (normally open config).... Or does this ground need to be isolated? 

Some Arduino applications use a resistor in a loop to the terminal and just short out the circuit with the pin to ground (machine frame). Is this better, or better yet does anyone have a proven method that has been used successfully.  I could also run an additional isolated ground from the board to the pin landing if needed? Thanks

[Bob at PMDX]

Yes, you can use the machine frame ground connected to the GND terminals on the PMDX-126.  These *are* isolated from the PC side of the PMDX-126.  My concern would be guaranteeing that the pogo pins make good electrical contact with the frame (no manufacturing crud/coolant/oil/grease/rust (gasp!) etc. gets in the way).

There is no need to an additional resistor in the circuit.  The PMDX-126 has built-in pull-up resistors.

The "proven" method is mechanical switches or proximity switches with the PMDX-126 GND to one terminal and the PMDX-126 input terminal to the other switch terminal.

Bob

[courter]

Thank for the help,  I have proximity limits now but they are too susceptible to temperature and I need to do "on the fly " re-homings during very long millings (open loop machine).

I will proceed using the drawing in 6.1 PMDX/C ,"Normally Open Switches" and run a ground bonding loop to the carriages. Thanks again, Edward