# Problem with mesuring value from current sensig pin on VNH2SP30

I connected the Monster Motor Shield (based on the VNH2SP30) to the Arduino Uno and successfully drive the engine, but I can not measure the value from the CS pin on this board (the voltage at this pin is proportional to the current flowing through the motor).     I measured the voltage value of this pin using a multimeter and it turned out that 1 ampere of load is equivalent 40 mV, 2A - 80 mV, etc.    But Arduino always shows a voltage of 0 V. I changed the AnalogReference to the Internal (the base value is 1.1V), but the result did not change (although at 40 mV the analogread should be about 37). With Arduino all okay, I checked with the help of voltage divider. The scheme on shilde is this: I suggested that the problem in the filter and replaced the 10K resistor with a 3.2K resistor, but that did not help. What is the problem with Arduino's strange behavior?

• Using the multimeter, what voltages do you measure at "ARDIONO A0" for the 1A and 2A test currents? – Jim Fischer May 2 '18 at 7:27
• @JimFischer about 40 mV for 1A, 77mV for 2A and about 0.1V for 2.5A test current. – Vadim Pavlovich May 2 '18 at 8:19
• @JimFischer Arduino can measure 2 units per 10mV. It's good resolution for me, because I make current protection for motor and in this case current was much greater than 2.5 A. But I don't understand why Arduino can't see this voltage. – Vadim Pavlovich May 2 '18 at 8:41
• I suggest you post the Arduino source code you're using to read the voltage at A0. Maybe someone can find a problem with the code. Also, have you tried using a different analog input? Maybe the A0 input is damaged (e.g., from electrical ovetstress (ESD)). – Jim Fischer May 2 '18 at 13:16
• @JimFischer I I already found the problem. It was necessary to connect the ground of Arduino with the ground of the battery (from which the motor worked). Of course grounds was connected through Monster Motor Shieled, but apparently it's not so simple with it. The extra wire on the minus battery to Arduino ground solved the problem. Many thanks for you responding. – Vadim Pavlovich May 2 '18 at 16:18