plasma torch switch relay for 5i25 / G540

Also, for the active high configuration to work as I want (relay not to click on when Linux CNC is closed) with a modded relay module (R1 jumpered over), the 1.41 V present on that DB25 pin would have to be too little to make the opto work. Estimating it would be ~1.03 mA with that voltage across the input of the opto and the LED. Could be iffy as some datasheets for the 817C opto show the CTR vs I_F graph going that low.

Does it matter if I grab that DB25 pin at the breakout board or at the terminal on the G540? Is there any other circuitry in the G540 that would prevent that 1.41 V state from occurring? It'd be nice to have that output only take on two states instead of three...

Well, apparently it does matter if you grab the output from the breakout board or the G540. I got rid of the vestigial CandCNC interface board that I had hanging off the G540 and connected everything directly to the G540's screw terminals. Also added a jumpered terminal strip to my setup to tie all the grounds together (might not be able to see all of the jumpers in the picture, but there are 5 of them tying all 6 columns together). Turned off inversion of the output in the HAL file and got the following results (relay module in active low mode):

LinuxCNC closed:

IN1 = 2.9 V
NO = open
NC = closed
LED = off

LinuxCNC open (any machine power or E-stop state):

same as above, but IN1 = 2.95 V

M03 command issued (have to specify speed on first one):

IN1 = 23.5 mV
NO = closed
NC = open
LED = on

M05 command issued:

IN1 = 2.96 V
NO = open
NC = closed
LED = off

So it looks like I can call the torch switch stuff finished (I just need to hook up the leads from the plasma to the relay output) and move on to getting the torch height control configured and wired up.

Thanks for all the help!

David