i said 20ma (thats milli - amps) which means its .020a
you guys just made a small calc error, happens all the time, and it was my fault for not making that clear earlier, so i am sorry about that.
milli is 3 places behind the decemil (shorthand m)
micro (shorthand is u, as in uA, the true symbol is really the greek letter Âµ but u is fine) is 6places behind,
nano is next (shorthand n) and its 9places behind,
and then peco (shorthand p) is 12 places behind.
those notations are always used for electronics, and are used for volts, amps, resistors (if ever) or watts.
12-3.3 = 8.7/20ma = 435ohms.
or the 4v source
4 - 3.3 /20ma = 35ohms.
i would suggest you go to radio shack to get your resistors and pot. they might be a little costly but its easier to do returns if you break something, or if you need more of something, and plus the difference in price + shipping is usually about equal to radioshack. the expection to this idea is leds, and some higher function digital and analog ic's.
its a little silly to buy 5 resistors and a pot from digikey, reistors are about 5cents a peice and a pots are usually under 2 bucks for a large ohm range, radioshack should charge you about 1 dollar for pack of 5 reistors and 1.50 - 2 for the pot.
anyway sorry for hte late reply, went over a friends house for a cookout, the food was great, but the company kept me out all night. lol if you need some more theory or advice just let me know.