I have a vintage mechanical tach & speedometer. I need to come up with a circuit to drive them with dc motors, either open loop, or closed loop.the source can be chopper wheel opto, or hall effect, or mag. pickup. I also need calibration. IE. actual road speed for speedometer. I have spent hours on the net looking at PWM circuits. My knowledge limitations are trying to add to, or alter those circuits. There must be somebody who has done something similar. Thank you ahead for your generosity in this forum, ...J.R.