Quote Originally Posted by The Master View Post
If a voltage reference chip does what i think it does then it sounds like a good idea and i might use one of those instead.
It probably does. But if you use high tolerance resistors, you should only need to calibrate once.

Ahh, ive always know V=IR as ohms law. Ive never seen E=IR before. Could that be a new / old or english / american thing?
2 peoples separated by a common language!

I think i understand that equation now.
P = IIR
ResistorWattage = Amps X Amps X ResistorOhms
Rapid sells some really low value resistors but they are a bit expensive. The only ones i see that are 0.1ohms or less are 50p each! I need 8 so thats £4.00 already (plus a bit for accidents). They are 4W though. Ill have to keep looking for some cheaper ones.
I think they're expensive because it takes soo much 'energy' (manufacturing energy, R&D, etc) to get them to those low low values and keep decent tolerance over a wide voltage/current/temperature range.

I always use 0.5W resistors but now i could use smaller ones in certain places depending on the amps and ohms.
1/4w are generally the cheapest, whether SMT or thru-hole.

I should start making a list of usefull formulas.
wikipedia...for instance
http://en.wikipedia.org/wiki/Ohm_law
http://en.wikipedia.org/wiki/Voltage
http://en.wikipedia.org/wiki/Electric_current
or my personal favorite...
http://en.wikibooks.org/wiki/Circuit...Resistive_Film
and so on and so on...
What is the voltage range of a PIC chips ADC input pins?
Vdd to Vss... It's all in the A/D section of the datasheets