On Tuesday, May 24, 2011, Olin Lathrop wrote: >> - Coil Power: 1200 mW >> - Nominal Voltage: 12Vdc >> - Coil Resistance: 120ohm > > If that's all you need, you can use much smaller packages. =A0All you nee= d is > a transistor that can withstand 12V and carry 100mA. =A0Just about anythi= ng > can do that. =A0Don't forget the diode to catch the coil kickback when tu= rning > off the relay else whatever transistor you choose will get fried. > > Something like a IRLML2502 should do nicely, but it doesn't need to be a > FET. =A0Especially considering your extreme cost sensitivity, you could u= se a > MMBT4401, emitter to ground, base to PIC pin with resistor in series. =A0= Let's > say you count on a minimum gain of 50. =A0That means you need a minimum o= f 2mA > base current. =A0To be pessimistic, let's say the B-E drop is 700mV. =A0T= hat > leaves 2.6V accross the base resistor. =A02.6V / 2mA =3D 1.3kOhms, so a 1= kOhm > resistor sounds about right. =A0The combination of MMBT4401 and 1KOhm res= istor > will cost a small fraction of a suitable FET. Would a VN2222 N channel MOSFET be suitable? Or an equivalent in surface mo= unt? I checked the datasheet and everything seems suitable, but there may be something I missed. Just checked your IRLML2502. Loving the current drain capability at Vgs =3D 3.3V. I guess I'll go with that. My only concern is that the SOT23 part will be a bit hard to solder by hand= .. My cost sensitivity isn't really toward $1 dollar components. I don't mind spending for those. I do, however, mind the $20 more per board for a few sq inches. That's unjustifiably unacceptable. But I found a good fab house so it shouldn't be that bad. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .