# Why is ground voltage non-zero, and why does it increase when I plug in an LED?

Here is the circuit (Arduino Due, 1kΩ resistor, LED):

Note how I bring the ground from the Arduino board to the breadboard, and also connect the ADC pin to the gnd rail on the breadboard.

Here is the code:

void setup() {
Serial.begin(9600);
}

void loop() {
Serial.print('\n');
}


Here is what I do:

• 600cs: I unplug the LED.
• 4000cs: I plug in the LED.
• 6500cs: I unplug the LED.
• 7750cs: I plug in the LED.

Here is the result:

I plug this same setup into an Uno, and I get no issue:

Why is ground voltage non-zero, and why does it increase when I plug in an LED? What issue with the Due could cause this?

• What is the question? – Leo Jun 26 '15 at 20:11
• please read the title! – Dave Jun 26 '15 at 20:12
• LED current * wiring resistance = ??? – Brian Drummond Jun 26 '15 at 20:13
• @Dave - Measure the resistance of each wire with a multimeter (maybe with one end on the LED lead so you include the breadboard resistance). Measure the current through the wire by putting your multimeter in series (in current measurement mode). Now you have LED current and wiring resistance. Multiply the two, and that's the expected voltage drop. – Justin Jun 26 '15 at 20:25
• Ground is zero by definition. Hence, what you're measuring isn't ground. – Adam Lawrence Jun 26 '15 at 20:41