Can you suggest reading for me Gerry or Al re the Mach PWM output?
I already have some excessive RC filtering (integration) on the pot input inside the super-PID, so it may accept the PWM signal directly or just require 2 resistors (for 10v to 5v conversion) and if needed, a 100uF cap (cap for extra PWM filtering).
CarveOne- great point about adding some type of option, thanks for that. At this point the SuperPID microcontroller has a spare pin that would only require tying HI or LO to select the linear/log pot option. But there is no terminal on the PCB so the wire would require soldering to the bottom of the PCB on the micro pins, which is a little clumsy.
It's very simple for me to just produce 2 firmware versions, one with the log system for manual pot use and one linear for external 0v-5v control, but I'm not sure Val would like that as the manufacturer as it adds complexity at his end, ie programming 2 versions, testing 2 versions, shipping the right version etc... Which is the reason the original design spec autoselects 50/60 Hz mains so it's never a manufacturing issue.
My limited understanding of Mach3 is that is uses "plug-ins" so can't this be coded as a plug-in? And what would be the down side if the speed range is not exactly linear, it would still be 5000 - 30000 RPM, and have a tacho display...
I forgot to mention the SuperPID comes standard with a logic-level "tacho" output as I had heard some PC software displays RPM on the PC screen, I don't know if this has any bearing.
(edit)Gerry, I juest checked out the Homann Designs DC-03, it looks like a nice product but I don't think that it would be necessary as it seems to be an isolation board and the Super-PID already has the low voltage stuff (typically) attached to the PC ground. At this point it looks like the Mach3 PWM output can just be attached directly to the Super-PID, maybe with an additional cap needed.