I am looking for an easy way to do 4-wire resistance measurements. I have already built a constant current circuit with a LM317 that outputs 100 mA.
Now I am looking for a way to measure the voltage drop. My first try was an INA219 breakout board where I have connected the voltage measuring probes directly to Vin+ and Vin- of the breakout board. The problem is the shunt voltage I see in the serial monitor is completely wrong. If I use a voltmeter I see the correct voltage drop and can calculate the value of my resistor for testing purposes. For example a 1,5 Ohm resistor should have a voltage drop of 0,15 V.
The INA219 outputs just about 8 mV, for a 10 Ohm resistor it outputs about 10 mV.
Is this kind of sensor not suitable for my application?
I would be very happy if anyone has an idea about what I am doing wrong!