Mesa 7i96 touch probe connection

OK so if the input common is connected to the negative of both the
24V and 5V power supplies, a 5V signal from the probe should actuate
the input (and input LED)

Is it possible that the probe output is open collector? (a switch to ground)
if so, it would need a pullup resistor to +5V to operate.

You should be able to measure the probe output signal with a voltmeter
If it does not change, it may need a pullup resistor.

I am not sure what you mean with the terms you are using.

This is the instructions I got to hook it up:
"To connect the probe ,connect red wire to +5V. Connect yellow to 5V supply's "-" terminal. Also , connect 5V supply's "-" terminal to your CNC board's "-"(ground) terminal. Connect the black terminal to your CNC board's probe input terminal.
The probe's black terminal is shorted to ground when tip is deflected."

So I have the yellow going to my -5v, red to +5v, and the black wire to TB3/IN4,

I hooked up my voltometer to my +5 and the negative lead to the black wire and when activated, it read 5v.

Basically if the probe signal is connected to the 7I96's input and measures
5V relative to the 7I96's input common, the 7I96 input LED will light and the
signal should read "true" in hal.

Hi pcw
I remember from my 7i76e:
I run io with 24v.
I have 5v signals from wireless probes. That did not work as when using 24v u need minimum 7-8v (if remember right). I use transistor for levelshift.
Mike

The 7I96 is a little different. it will sense 4V to 24V signals
But if you have the input common at +24V It cannot sense +5V signals.
(you would connect the input common to +24V for example if you used
NPN proximity switches which ground their outputs when active)

If the input common is at 0V it can sense positive 4V to 24V signals
My guess is that the either OP does not have the input common at 0V
and connected to the probe common terminal. Or that the probe has
a open collector (NPN) type output and will not supply 5V to a load
without an external pullup resistor.

I think I need the pullup resistor, but I am not sure how I would calculate the value I need.