THCAD

phillc54 wrote: I am looking at some document changes and I want to mention some practical options for users.

At the price point, nothing can compare to the THCAD. A friend costed some of the components on it and could not work out how PCW did it for USD $69!

phillc54 wrote: I think the Arduino way would use serial and that would only be userspace wouldn't it.

Not really, with some clever programming arduino can output up to 1MHz on outputs, ESP can do more.
Using that output to a fast opto would be enough to wire it directly to encoder input. No serial.

rodw wrote: At the price point, nothing can compare to the THCAD. A friend costed some of the components on it and could not work out how PCW did it for USD $69!

Just the time to make any of the above would prove more costly, and the reliability and functionality would be nowhere near what THCAD offers.

I would guess someone clever enough to go down that route wouldn't require connection instructions in the docs.

phillc54 wrote: I would guess someone clever enough to go down that route wouldn't require connection instructions in the docs.

Not really.
Times have changed, 30 years ago knowing electronics meant really knowing how things work and what everything does in a circuit. Nowadays, anyone who made the arduino LED blink thinks he knows electronics and programming !

I think I will stick with "readily available"

You keep coming back to encoder inputs. There must be other methods to get an analog signal into linuxcnc.

You might be able to use the GPIO on a Raspberry .

But we are not talking about done for you modules and you come back to the THCAD as the only viable option unless you are using ethercat. But if you go that way its not something for the hobbyist and you will want deep pockets.

And they definitely won't need your instructions.....

I think the docs only need to be for practical off the shelf methods, anything DIY is out of scope.

Every computer has at least two analogue inputs that can be used for that, albeit very limited in sensitivity! Audio inputs. They are usually +-1V PP, so a total of 2V usable

The real issue for THC is that for best performance you need an isolated sensor
this is because you want to measure the voltage between the work and the torch
The work connection is theoretically at ground potential but may differ by a few volts
DC and worse may have significant continuous HF noise and large spikes when the arc
is established. (due the the finite inductance of the ground path and the ability of the arc to generate very fast current steps)

In addition to measurement considerations, you really don't want the very dirty plasma source ground connected to the control system ground, creating a ground loop.

This is not saying you can not make a simple isolated measurement system, heck, you could use a 555 timer rigged up as a V-F converter and a low cost OPTO and have a
working isolated measurement system for less than $1.00. (though you still need an
isolated power supply and this is a bit tricky since this isolated supply may provide
a path for HF currents into the control system)