=20 > CMOS Schmitt trigger I did suggest the 4001 - oscillator and monostable Lindy - Monostable, or triggered pulse generator, using the TTL equivalent, 74LS02 http://www.electronics-tutorials.ws/waveforms/monostable.html Ideas galore, and explanations too. Very much worth a look =20 http://www.doctronics.co.uk/4001.htm 3.4.3. Gated NOR oscillator http://www.doctronics.co.uk/DDE/DDE_03.html Joe --=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 .