# 2 voltage measurements same circuit Arduino Uno

I want to measure a simple circuit. From the battery it leads to an amperemeter to an 1 Ohm resistor to a 5 Ohm resistor and back to the battery.

The voltage that needs to be measured is that of the battery and the voltage drop over the 1 Ohm resistor to determine the flowing current via I=U/R . If i connect the circuit to Arduino board and do just one measurement, everything works fine (1.2V battery, 6 Ohm resistance, arduino gives 0.2A for current {after conversion} ), if i connect the second one, it seems that a short circuit via GND is created because the current rises to 1.3A. Is there a way to solve this?

• you have two terminals marked ground. Relabel your circuit with only one ground, and try again. – Neil_UK Apr 28 '17 at 7:48
• @Neil_UK im sorry i dont get what you mean. The terminal lines to PinA2/GND and PinA1/GND are supposed to be the voltage measurements using the Arduino AnalogIn Pins 1 and 2 . Arduino board also has 3 GND pins. Since they are connected as i understand from the behaviour of the current, I do not know how to continue since the arduino measures the AnalogIn voltage by comparing it to ground if I'm correct. – Anton Welisch Apr 28 '17 at 7:51

All arduino ground pins are connected together. If you connect a ground pin to each side of the 5ohm resistor, then it short-circuits the resistor.

Put everything on the same schematic, and just have one node labelled ground. It's much easier to see what's going on if we put ground at the bottom, and put components vertically, following their voltage (when we can). For instance like this ... simulate this circuit – Schematic created using CircuitLab

The voltage across each component can be computed as the differences of voltage you measure at each node. So your battery voltage and R2 voltage are measured directly, the R1 voltage and ammeter voltage drop have to be computed.

Note how giving the components numbers, aka reference designators, makes it easy to talk about specific components, another tip for drawing of schematics. 'The 5ohm resistor' works for circuits of this size, but runs out of steam if you have two 5 ohm resistors, or values change.

• Thanks a lot! Now i get what you meant before. After rewiring to your circuit it works. I will keep to your system for the schematics in the future – Anton Welisch Apr 28 '17 at 9:25