On Sat, Oct 1, 2011 at 11:26 PM, doug metzler wrote= : > I was originally planning on running the FETS in the linear region but > I couldn't get a smooth enough ramp up via the potentiometer, so I > went to PWM and a small microcontroller, but probably could have done > it with a 555. > That region seems to be very tight. I don't know if you can do it with a capacitor and PWM reliably. I think and opamp is the only way to go with an analog feed into the opamp. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .