I’m using mach4 and pmdx 424 board. When I probe down with a G31 to touch the set plate, when it touch the plate it will jump maybe .010. Not sure way this is happening. It does not do it all the time 1 out of 3 times. It will continue with the rest of the routine but the dro in mach4 will be off.
Any help would be great.

Hi,
what is the build number of Mach4 that you are using?

I had a bit of a battle with one of the earlier builds. What you have described sounds like noise causing false triggering. Is it possible to lightly 'load' your
probe circuit so that its less inclined to pick up induced noise?

Craig

Mach4 build that I have is 3481. The only time it will do this is when the tool touches the plate. Not sure about loading?? How do I load it?

I think what Craig was referring to was putting a resistor on the input signal. Maybe a 10K ohm. That will make it so it requires more current for the signal to change state.

Tweakie explains it well here.

http://www.machsupport.com/forum/index.php/topic,16323.msg110342.html#msg110342

Tweakie also has an awesome post in open builds where he talks about wiring strategy and using capacitors to help mitigate noise.

https://openbuilds.com/threads/electronics-101.693/

So I will need to put a 10k in line at the bob. This will go between the bob and the probe wire?

Hi,
no not quite.

With the probe hooked up to your BoB then the probe wire itself is 'floating', that is to say that one end is hooked to the BoB but the other end isn't. That piece
of wire acts like an aerial and could pick up enough noise voltage for the BoB to think that the probe has made contact but it hasn't. What I would suggest is put
a high value resistor from your probe wire to earth. What you are hoping to achieve is put enough load to damp out any noise but not so much that the BoB thinks
the probe is shorted to earth.

Depending on the sensitivity of the BoB it may not work, any realistic value resistor would be detected as a probe contact if the BoB is very sensitive. A small capacitor
might help, say 470pf or there abouts from the probe to earth.

Craig

So I will need to put a 10k in line at the bob. This will go between the bob and the probe wire?

Best to connect a 10k resistor between the probe wire and +5 Volts (at the BoB end).

Tweakie.

Does the type of wire that leads to the touch off plate make any difference? Should I you a shielded wire as well
Thanks everyone for all the help on this.

Anything that is using 5V should be shielded IMO. But then again, 5V should never leave the cabinet IMO eiher so.....