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In both cases you measure voltage. If you use current shunt for measuring you should use OpAmp to amp voltage from mV range 50mV-100mV to 0V-4,5V (5V). In uC software you make calc that showing digit on display means amperage.
The load at the op amp output will give some proportional voltage for input current. That voltage should be in the range of 0v to 5v for adc input. So you are giving dc volt as adc input.
actual current is 2 mA. Op-amp o/p is 2V, say. adc vref+ is 5v. So, adc max value is 1023 for 5v but the voltage is 2v.
for 2v adc input adc reading is 409.2
409.2 represents 2v and also 2 mA
(409.2 * 5) / 1023 = 2. It can be either 2V or 2 mA.
but guys for shaunt resistor and opamp methords, the amperage and voltage must be in proportion like.....4volts and 4 amperes.....what should i do if my batteries are of 4.2v and can pump out 3c current?
Shunt resistor will waste battery power, I suggest usage of Hall sensor, but its your project. Why not to try, maybe you have "Die hard" mark of battery. ;-)
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