Pic Ammeter

[majoka]

@ ero
it work gud for me but can u tell or provide some calculations for resistors that how u choose these values becoz i also spent one week to use op amp LM358 as a non inverting amplifier with its gain almost 500. but its behavior was non linear but in ur case its behaviour is linear
kindly tell me about calculations it will be useful for me in future designing

[ero]

Dear Majoka,

Normally I do not make a lot of calculation in that cases. I use simulator (isis) and I change the resistance value until I find the right output. If you need to make the calculation here are the formulas which I use time by time for rough figures.
In order to findout (Vin ) voltage I use V=I*R which is basic Ohm rule.
For instance one of our cases I had use the current resistor 0,05 Ohm and it has created about 5 Amp. current on the entrance of the circuit.
V=0,05 x 5 A=0,25 V. Using this figure on Opm-amp formula ;
Voutput= Vin *(1+Rgain/Rin)
Vo=0,25 *(1+19K/1K)=0,25 * 20K = 5V and the circuit produce 5V which is right voltage for Pic measuring.

If you look the case from opposite side you need 5V on the output and you need to find the value of Gain-resistor. You put the values to the formula and you pull and find the value of Gain resistor from same formula.
5V=0,25V (1+Rg/1k)
5V=0,25 * (1+Rg)
5V=0,25+0,25 Rg
Rg=(5-0,25)/0,25 = 19K

İt is better to use one fixed resistor and serially one variable resistor all the time. The value of the variable resistor must be as much as small in order to make a precision regulation.

I have to tell you I am an amateur not electronic educated person. But I read a lot about the electronic.
Rgds
Ero

[majoka]

thank u so much ero i also use isis but i was doing a mistake that my input was too low as compare to your case i was multiplaying a 0.02m volt to gain then 0.04 ,0.06 and so that why its behaviour was non linear becoz op amp can not significant difference at output for such low input
even i use same formulas for calculation
i adjust Rf=1k ,Ri=1k nw according to formula
Vout=vin*(1+(Rf/Rin))
vout=0.02mv*2=0.04mv
nw i was expecting to 0.04 but it was the limitation of the op amp nw i understand
thank u again dear i understand it