"Karl Townsend" wrote in message
anews.com...
I need to control a pot with my CNC control. One option is to get a pot
turner like this:
http://www.cnc4pc.com/Store/osc/prod...roducts_id=179

This would work but I'm not real keen on having a device to physically
turn a knob.


I've got a whacky idea that I'd like to run past the EE types in the
group. I have a large number of unused Opto 22 digital outputs
http://www.opto22.com/site/pr_detail...=4&item=G4ODC5

For sake of argument, lets keep the numbers simple. Get four resistors,
100, 200, 400, 800 ohm in series in place of the pot. In parallel with
each resistor put an opto output. Then using base two, any resistance from
0 to 1500 ohms is possible. The switch time on these outs is 100
microseconds - I'm thinking a pot to control power level on the plasma
cutter couldn't possibly notice the switch time. I don't know if these
devices will work at 0 volt between the otpo 22 output connections.

Or is there another easy way to do a pot with a CNC control?

Karl


There are motorized potentiometers like some stereo's use with remote volume
control. There is also a digital pot that acts like a motorized pot. I've
seen the equivalent circuits for digital pots, you could make an equivalent.
For example, make a 2K ohm resistance using 10ea 200 ohm resistors in
series, the voltage output depends on the junction you select with an analog
switch. It may be a better solution to use some sort of digital pot, if you
can't find a digital pot to work with 24V you could use an op-amp to change
the voltage you can get from the pot (or DAC for that mater) to the 0-24V
range.

Parallax has some digital pots on their website, complete with datasheets
and source code for the Basic Stamp.

But for CNC control, I would probably just use a 0-10V analog output, like I
do for my spindle speed, and amplify it to 0-24V. If you wanted you could
control your pot output with your S command.

RogerN