The application was a rewind control on a rather elderly commercial printing press.

The original setup was a commercial PID board made up of *many* op amps. At its best it was cranky acting when it was working well, and it had been going flaky for some time. When it finally failed, and I determined that it had chips on it that I had no idea how to get and that the OEM had discontinued the board long ago, I decided to replace it with a digital implementation.

The system consists of a 50HP speed regulator DC drive and a control board that accepted an input from a pot set by the machine operator that determined the desired dancer position (check out Wiki or the like if you're not up on compressed air loaded printing press dancer rewind setups). A gear driven pot provided feedback from the dancer, indicating its position.

The drive required a 0-15VDC reference signal. I built up a board consisting of a +18 and +5 supply. +5 supply was run out to the operator and dancer pots. Those two signals became setpoint and feedback, respectively, and were dumped directly into PIC A/D pins. Half of a LM358 op amp fed by a simple RC filter took the PIC PWM output, smoothed it, and raised it to 0-15VDC.

My calling app sets the reference voltage to the drive to zero should the PID routine ever call for a negative, but that's probably superfluous.

Took less than an hour to set up the P, I & D constants to achieve better dancer control than the original had *ever* provided.

I have no doubt that the identical hardware, with no changes other than retuning in software, could do a perfectly acceptable job in any web material rewinding application. And speed regulator drives are simpler to set up, less expensive, and more readily available than the torque regulator drives that I've used in similar applications in the past.

Again, thanks for your help and use of a very handy routine!

Mike