Reading NPN open collector signals with cRIO DI/O module?

[Sean GT]

I want to wire a shaft encoder with NPN open collector signal wires to a NI 9403 DI/O module in a compactRIO. Ideally I want to do this without requiring the use of an additional external voltage source and pull up resistors. My idea was to use extra DI/O lines configured as outputs set to logic high and wire these (possibly adding resistors) to the signal input lines connected elsewhere on the DI/O module.

My questions are:

(1) Will this work?

(2) Can connecting a DI/O output pin to ground do damage to the module?

[Brian_P]

This would be a bad idea, the DO can output 63mA maximum and could definitly blow your card,  also connecting DI/O output to ground could short and cause damage to your device.  This is not recommended.

[Tom__Sedlack]

Your idea should work if:

1)  Use a pull-up resistor (10K or so) from a DO line acting as a power supply to the O.C. output of the encoder.

2)  Connect the pulled up O.C. output to a DI line to read the encoder channel.

3)  Repeat 1&2 for each encoder channel you want to read (A, B, and Z).  

No sharing between signals.  3 signals, 3 pull-up resistors, 3 output channels set to high, 3 input channels to read.

or use a different DIO module that has built in pull-ups.