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That's what I thought, the problem is that many drivers have differential feedback encoder outputs and I would have to use another IC to convert +Z - Z to Z.

unknown wrote:

... it aggravates me when I see opto circuits with the input and output sides connected to a common ground.

+1

langdons wrote:

A really big relay should not need arc suppression.

Please do some research before making such statements, especially after it has been answered by a VERY experienced member of this forum.
And who asked about MosFET's ?

I'm pretty sure Tommy would disagree with that, personally I've never had any issues with HP gear, even the ancient server I was running 24/7.
I'd say that there are quite a few HP machines running Linuxcnc that never give any issues.

Yeah, a manual MPG shouldn't require reading at the same rate as would be required for spindle encoder.
Just remember that the RPi io is only 3.3v tolerant, so a way of translating the MPG signal voltage and protecting the RPi io from noise.
The 74lvc series are 3.3v devices that are 5v tolerant on their inputs.

so your saying take the Pi GPIO and put it on a server thread not on a realtime thread?

Some do some don't, you'll need to check the data sheets.
The role of the diode is to protect the driving circuit from the reverse voltage generated from the collapse of the magnetic coil. No flyback will eventually cause component failure, a far bigger issue than EMI.
I'd take PCW's advice.
Another thing I would look at is the routing of your wiring and ensuring physical seperation of control and AC, if you haven't already taken care of this issue.
If you do use optos make sure that the input side and output side are powered by seperate PSUs and the ground are not connected, it aggravates me when I see opto circuits with the input and output sides connected to a common ground.

The issue here is that the relays are switching a 120VAC solenoid.

Because the solenoid is an inductive load, this will cause massive EMI unless
there is contact arc suppression across the relay contacts. This can be done
with a bipolar TVS diode, a MOV or an RC arc suppressor.

Flyback diodes might increase contact arcing becuase they slow down the release of relay contacts.

Shouldn't be an issue, as all you you are doing is adding another function, servo thread should be ok for MPG.
Give it a go and see what happens.

Redacted.

Thanks for this Chris, especially pleased to seeing the lathe part getting TLC 

I switched to develop branch and did the uninstall and reinstall, went like a charm!
I noticed that unlike Gmoccapy issuing G43 doesn't update the active G codes, G49 remains, is that expected?

Now for the newby bit, does tool touch off only work with an active (or passive) probe, so I need a probe wired in and configured to set tool offsets?
Or is this a G49 artifact from above?

Thanks again for this awesome interface and your work!

Then you need arc suppressors across the relay contacts.

Possibly something like this:

www.digikey.com/en/products/detail/bourn...OV-10D201KTR/2408223

Note that it looks like the relays have their own drivers, so the 7I95T does not need
any flyback diodes.

They are 120v ac so unfortunately can't use flyback diode.

The solenoids are ac 120v. So I can't use a flyback diode on them. Its the relay coil that is giving me spikes going back to the mesa 7i95t. So I need to stop that.