On Sat, Jan 2, 2010 at 8:02 PM, Jason <[email protected]> wrote: > DJ Delorie wrote: >>> I'm concerned about leakage. This device will probably sit on a >>> shelf for some time (with battery inserted, pic in sleep mode). I >>> wanted to make sure there wasn't a trickle of current through the >>> motor. >> >> Perhaps you could tie 4-5 PIC pins together to get the needed current? >> > > Not possible. I have only three output pins and the other two are in > use. :-( > >> Otherwise, look for the smallest MOSFET that will handle your current, >> as smaller size usually means smaller leakage current. For example, >> the Fairchild 2N7002K (SOT-23) leaks 1 uA when off (Vgs == 0) but the >> 2N7002T (SOT-523) leaks only 1 nA when off. The 1G125 "leaks" 10 uA >> when on (Icc). >> > > Awesome, thanks! That was exactly what I was missing. I'll take a look > at the 2N7002T more carefully in the morning. > > thx, > > Jason. > > > _______________________________________________ > geda-user mailing list > [email protected] > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user >
You will want to use a N-channel FET, a flyback diode across the motor, and you will brown out your battery without bulk capacitance. Here is a link to a cr2032 data sheet <http://data.energizer.com/PDFs/cr2032.pdf> I had a hell of a time driving a 50mA IR LED with these coin cells, A 100mA motor will be tricky too. It has a 6.8 mA pulse load with 400 Ohms series resistance at 2.7 volts. You will need bulk capacitance and to protect the uC from browning out. Think of a coin cell as using a kitchen faucet to run a fire hose. I would thoroughly suggest that you look into the real current draw of the motors. How long they will pulse for etc.... Pick up a copy of the art of electronics, and some of the Forest M Mims III books they will have circuits for driving small motors in them. Best of luck. Steve _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
