ok so im at home and i needed a way to measure the current draw of a current project for work and i wanted to do it in the most basic of ways possible so i just stuck my cheap mastech in to uA mode and measured it on that ... the impedance was way to high for the 3.3v logic and got way too much voltage drop
i do not own a uCurrent as im broke
(tho id love one when i get the cash!)
so i scoured the parts bin and i had a left over ICL7650SCPA (datasheet
http://www.intersil.com/content/dam/Intersil/documents/fn29/fn2920.pdf ) 2mhz 'super' chopper amplifier ... massive overkill but ok!
i made this simple circuit based entirely off the uCurrnet (thanks dave!)
And with all off the shelf 5% resistors and cheap jumpers on a breadboard with only 1 decoupling cap i got these results!
Tested with a voltagestandard.com calabrated voltage and current standard thats only like 3 monts in cal ... for the 1ma test i used the 1ma 2ppm source on it, for the 50 and 500 uA tests i used the 2ppm resistors (the 10k and 100k) and the calibrated 5v out
^
1mA
^
500uA
^
50uA
IM NOT SAYING THIS IS SOMETHING TO MAKE FOR PRECISION I SIMPLY GOT LUCKY Why does this work? Undeniable proof that there is a god?
no like everything else it can be explained with science!
for one i got an AMAZING opamp in there ... there about $6 a peace and in this setup has an offset at the lowest voltage i can measure ... 0.0mv and
yes my meter was calibrated (manually) to have the voltage as dead on (tested with the voltagestandard.com standard but it was calabrated in my unis cal lab)
Secondly all the resistors are from one lot and have about the same resistance deviation
Third i got lucky with my 100k and 1k having a ratio of 99,100 (not exactly but with my rough math)
Forth i have central air so the temperature remains stable
Fifth its powered off batteries and my house has very low ambient noise
AGAIN DONT TAKE THIS AS AN EXCUSE TO SWAP OUT YOUR 0.5% RESISTORS FOR 5% ... i was LUCKY and yes thats an end table ... dont ask XP