Hi Marcel, Thanks for your suggestions too, great ideas. The fets switch the unregulated votage, and are driven by the 9 volt supply. The 5.6 volt only runs the micro, an LM339 op amp and a intermediate chip that drives the fets (It's late 1.30am and the gear is in the w/shop :) ) .. so that shouldn't cause any problems, but I will certainly try it anyway. I understand that any unused inputs should be clamped. I'll check the PIC16F616's specs too, I wasn't aware of that sort of feature. Thanks again for the suggestions. Regards, Roger From: "Marcel Duchamp" > Roger Weichert wrote: >> Hi Guys, >> >> >> SUPPLY . Crudely, the boards only use a 5.6v zener to regulate the supply >> to >> the original micro and two other housekeeping IC's . so I assume that >> needs >> to be addressed. >> >> The board runs off 12V ac, via a rectifier into a 22000uF cap. Then it >> has a >> 82 ohm resistor, a zener to drop it to 9 volts . then another resistor >> (120 >> ohm) and the 5.6 volt zener mentioned above .. crude !! .. but they've >> been running for 20 + years. >> > > Just in case... you should check that the board will run fine at 5V > instead of 5.6V; modify one and verify that they work at 5V. Check FET > gate drive levels and look up the specs to be sure you will be able to > turn them on completely. If everything works fine at 5V then you might > consider the PIC16F616 - it has an internal shunt regulator. I think > there are others in that series as well. It would make the mod simpler. > > Alternatively, if the board does work fine at 5V, you can probably > change out the 5.6V zener for a 5.1V unit and then use any 5V rated PIC. > > Other hardware issues to watch for are PIC pins that float during reset > - is that compatible with the existing circuitry? You may or may not > need to address that with pull-ups/pull-downs, etc. > > It sounds very do-able! > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist