# Pulsed DC current measurement using arduino and shunt resistor

I am currently working on a project ( to develop a constant current pulsed DC supply) in which current has to be measured using Arduino's analog input (Upto 20A) passing through a variable resistance RV1(shown now as 145 ohm).

Current through this resistor is measured using a shunt R1 of .0035 ohm. Capacity 20A-AC/70 mV max.

For that, an IC4559 Difference-Amplifier is used as shown below. I have set the gain to 70. as 70*.070 Volts gives 4.9 Volts, reaching to the Arduino analog input port's capacity.

Question: This configuration works, but in my original circuit there is no grounding near the Diodes (highlighted). When I remove the ground port near the Diodes, the value read by Arduino become absurd, is there any way to measure the load current without grounding the diodes by using the similar configuration?

Arduino Code:

void loop() { lcd.clear(); volts = analogRead(A0); lcd.print(volts); Serial.println(volts); delay(500); } 

• Instead of that shunt+amplifier circuitry consider just using a Hall-effect sensor (ACS714). Available in different current ranges (up to 30A), 1.2mOhm internal resistance and galvanic isolation of 2kV. A single chip, no hassles. – JimmyB Jun 25 '19 at 12:10