I dont know about a voltage reference chip. I was thinking to have a variable resistor to get it more or less calibrated properly then have an offset value that can be set by the PC so i can fine tune it without opening everything up to get to the PCB. 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.
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?
I think if i calculate the wattage of resistor i need then double it i should be alright. Im going to put a safety cut out on too so if either AC or DC tries to draw too much current it will warn you on the PC screen and if it goes over a certain value it will cut the power to that transformer. A PIC chip will control cutting it off (the PC just sets the values) so it should be pretty quick to cut the power incase of a short etc.
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.
Thanx for that formula. I think it will help with other circuits too. I always use 0.5W resistors but now i could use smaller ones in certain places depending on the amps and ohms. I should start making a list of usefull formulas.
What is the voltage range of a PIC chips ADC input pins? Im sure i could find the lowest value out by trying it but i want to find out the highest value too without releasing the mysterious blue smoke
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