> Looks OK by and large. Not entirely sure what's the point of having >the subsidiary 9V rail capacitor larger than the main reservoir cap, the >other way round would seem more intuitive but maybe I'm wrong. > Actually - make sense to me - you want the PIC to power up faster than 40 mSec or you are likely to have weird reset problems. I use something very similar, except adapted for 120 Vac 60 Hz. My inrush limiting resistor is either 150R 0.5W (with 1 uF input cap) or 2 - 150R 0.5W resistors in parallel with a 2u2 input cap. I also put a LED and series 150R resistor in parallel with the inrush limiting resistor as a power indicator. The importtant thing here is that the inrush resistor is much larger than you would normally expect, with the resistor being carbon composition instead of film. Getting back to the original circuit Jinx posted, I would change the 1n914 diode (at the line sample input on the PIC) to a 4v7 xener. It doesn't cost much more than the 1n914 and ensures that the PIC input doesn't see high voltage. This is especially important if the sample gies to input GP3 on an 8 pin pic. The only other thing I use on some furnace controllers is a reset derived from the 5V supply. I use a cheapie pnp transistor (2n4403) wired with E to 5V rail, B to 4v3 zener cathode, C to reset with a pulldown resistor to gnd and a 100n cap from reset to vcc (across C-E of the transistor). Value of the pulldown depends whether I'm using an 8 pin pic or larger - the 8 pin PICs have a built in pullup which requires a lower value of pulldown resistor than normal. The anode of the 4v3 zener goes directly to gnd - the transistor / zener combo replaces the 5v zener in the original circuit. This has the advantage of holding the PIC in reset until the zener is conducting - the 100n cap across the transistor stops small transients from resetting the pic. Shipped many thousands of those with NO failures. Hope these comments help. dwayne Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 15 years of Engineering Innovation (1984 - 1999) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. My posting messages to Usenet neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email.