THC plasma configs, with HOW TO.

Hello!

-- avoiding to open another thread

Let me recap my current understanding of THC: it has two modes, one that reads the arc voltage trough a THCAD board (outputs frequency translated to voltage) and logic happen within LinuxCNC and another where an external "device" sends up and down commands. Hope this is correct.

My goal is to create a simple and cheap machine driven by a board PC (eg. Raspberry).

Since i already have GPIO pins, this should be easy, however Raspberry does not have a ADC.

My options:

1. Use an external board with embedded ADC and logic (arduino), hook to a voltage divider and send up-down commands - not preferred since i would like to use LinuxCNC logic

2. Use an external ADC and voltage divider and send the value to the raspberry (i2c) - can LinuxCNC be configured to interpret the value received over i2c?

3. Use a THCAD board and read the frequency over a GPIO pin. Would the resolution be limited by the RPI?

4. Use Arduino that reads voltage and outputs a frequency so that the LinuxCNC can apply its internal logic - simulate a THCAD basically. Would this even work?

Are those options viable? What is your advice?

Thanks,
Alex

There is not really anything simple or cheap about plasma. the Pi is supported. The Pi V 4 is more or less required for reasonable performance.

1. I would not recommend Too much work.
2. I think there is a bit banging i2c component but its not high performance
3. You could do this if you use the encoder component but throughput will be limited.
4. You do not need a arduino. Mesa says "A functional THC A-D could be made for $2.00 with a 555 Timer VCO and an optoisolater."

5. Use a Mesa 7C81 to utilise the Pi GPIO store.mesanet.com/index.php?route=produc...oduct&product_id=338
6. Consider using a 7i96 and a thcad with your pi. This might cost a bit more but means you are not tied to the pi so can upgrade to a pc if you want later.

alex.statie wrote: Let me recap my current understanding of THC: it has two modes, one that reads the arc voltage trough a THCAD board (outputs frequency translated to voltage) and logic happen within LinuxCNC and another where an external "device" sends up and down commands. Hope this is correct.

Yes, that is correct.

alex.statie wrote: 1. Use an external board with embedded ADC and logic (arduino), hook to a voltage divider and send up-down commands - not preferred since i would like to use LinuxCNC logic

That will work, choose an arduino with 12BIT analogue inputs, it will have better resolution. Add optocouplers to the outputs, isolated power supply, the possibility to produce ARC OK signal from the voltage that should be settable as min and max.

alex.statie wrote: 2. Use an external ADC and voltage divider and send the value to the raspberry (i2c) - can LinuxCNC be configured to interpret the value received over i2c?

TI makes some 3$ chips that do voltage to frequency conversion, they can do 10KHz, 8pin DIP package, forgot the model number, i still have 3 of them collecting dust.

alex.statie wrote: 3. Use a THCAD board and read the frequency over a GPIO pin. Would the resolution be limited by the RPI?

Should work, but probably very limited due to RPI GPIO way of doing things.

alex.statie wrote:
4. Use Arduino that reads voltage and outputs a frequency so that the LinuxCNC can apply its internal logic - simulate a THCAD basically. Would this even work?

This works and makes it a bit simpler as you need only one optoisolated output from the arduino to the PC, again read under number 1 for the rest.

tommylight wrote: TI makes some 3$ chips that do voltage to frequency conversion, they can do 10KHz, 8pin DIP package, forgot the model number, i still have 3 of them collecting dust.

That chip is i think lm331.
There are premade modules on ebay and aliexpress. Try searching "Voltage to frequency converter". 0-10V to 0-10khz.

Use Arduino that reads voltage and outputs a frequency so that the LinuxCNC can apply its internal logic - simulate a THCAD basically. Would this even work?

I am going to try this this week. Will report about functionality with parallel port BOB.

pinder wrote: That chip is i think lm331.

That is it.

Thc up doun arc ok www.chipmaker.ru/topic/189305/