Arduino potentiometer example: what limits the current?

Question

I have a question regarding potentiometer example:

https://www.arduino.cc/en/Tutorial/AnalogReadSerial

If I turn the potentiometer to the marginal position and have 5V at A0 (and almost zero resistance at the pot), what limits the current flowing through the circuit?

Answer 1

A0 input is high impedance, so very little current is flowing into A0. The value is so small that you can simplify that it flows only from +5V through the potentiometer to GND.

For some applications, when you are measuring high-impedance sources (a source that can deliver very little current) this simplification may not be correct.

You can find more detailed explaination in Atmel application note:

http://www.atmel.com/images/atmel-8456-8-and-32-bit-avr-microcontrollers-avr127-understanding-adc-parameters_application-note.pdf

Answer 2

Assuming A0 is set to input then it is a high-impedance input. That is, the input has a high resistance, and only consumes enough current to "sample" the voltage.