> What I wanted was a 10us pulse every second or so, If accuracy of either pulse is "not too tight" [tm] a quick and easy result can be achieved with a hex Schmitt trigger IC and a few passives. CD40106 74C14 74HC14 4584? ... 1 gate is a 1 Hz oscillator, 50/50 mark space. 1 megohm, 1 uF approx. or 100k, 10 u, or 10M, 0.1 uF. Play. This triggers a 2nd gate as a monostable - C2 from IC1out to IC2 in R2 IC2in to ground (or Vdd) Diode (optional) across R2 (Schottky pref) polarity discussed below. If R2 is to ground then when C1out goes high C2 is driven high so IC2in goes high and IC2out goes low. R2 then discharge C2 and after 1 time constant gate output goes high again. When IC1iout again goes low IC2in is driven to about -Vdd. It will discharge back to ground long before next cycle starts. Having a diode across it hastens this process and prevents gate seeing larger than expected -ve bias. Diode is not really needed here for resetting as pulse is v short wrt duty cycle. Does no harm as a voltage limiter. Pulse length is governed by R2/C2 time constant. Such gates typically have Schmitt thresholds of 1/3 and 2/3 of supply. These vary amongst production batches and some model ICs have different Schmitt limits (Nat Semi ?4584? was different).(Lonnnng ago). To reverse pulse polarity take R2 to other rail. Reverse diode polarity if used. ________________________ The 74C14 and friends is amongst the most useful ICs available for low cost low power analog-digital shadow world playing. Place a resistor from out to in. Drive input with an audio signal of about 2/3 Vdd peak to peak centred on 1/2 Vdd. Voila - PWM :-) Much much much more can be done with them. Approaches magic. eg Longish ago (2001?) I made a low power low cost boost converter using one that got used in a Taiwanese produced volume product. That plus an LDO and two transistors, an inductor and some glue parts provided 5V for the electronics in exercise consoles when failing batteries dipped badly when a motor driven load-control-actuator activated. Worked superbly). LDO used the trick that I 'invented' but which Olin did independently and no doubt 100's of others did before me of having a transistor driven by Vin-Vout differential so LDO maintained about 1 Vbe from Vo to Vin. This transistor linearly adjusted the 74C14 oscillator duty cycle. Yee ha :-). [Taiwanese LDO was extremely well priced, making overall circuit extremely low cost compared to more conventional alternatives.][Taiwanese factory engineer could not believe the results - got out his box of nasty old dead high impedance batteries and was suitably impressed :-) ]. Russell McMahon Applied Technology ltd New Zealand --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .