so i'm planning to build a battery power meter where it will measure voltage,current,mAh,WH ,and i have created the voltage divider for voltage measurement ,but i cant decide which current measuring method to use,i have 3 method that will work,but which one is the best , i want it to be as accurate as possible ?
also the microcontroller i will be using is an atmel atmega328p-pu used as standalone micro controller
the first method (A) is by simply using a power resistor as current shunt on negative rail and when its under load there will be a little voltage drop on the resistor and the mcu will measure the current from the vdrop
second method (B) is by using a CT and an op amp
third method (c) is by using custom callibrated ebay current shunt since the current shunt will only gives out few millivolt it will require an op amp,and because this kind of shunt was very sensitive to temperature change a thermistor is required to compromise the temp changes ,because temp change may cause the reading to go off so badly example: current shunt output is 1mV/A at 36c it may change to 1.1 or even up to 2.6 mV/A due to temperature change.