Arduino ADC input: Will using internal pull up resistor add or reduce power consumption?

Discussion in 'Embedded Systems and Microcontrollers' started by camjerlams, Jul 8, 2016.

  1. camjerlams

    Thread Starter Member

    Dec 23, 2012
    So this is my first arduino project, I am switching a transistor from pin13 when the voltage on A0 (ADC) falls below a certain value.
    It's going to water my plant while I'm away for three weeks and it has to run on batteries so I dont want to waste any power. There will be 5V at the A0 pin >90% of the time, but when it takes soil resistance readings every 12hrs or so it will drop a few volts at that pin.

    Will there be any current leakage into the arduino while it has 5V on A0?
    Will there be current leakage through the pull up resistor if I use it?
    Is it negligible?
    If not, which is the most efficient option/less leakage?

    Also one more thing: I'm using a ULN2803 darlington array to switch the motor, do these ICs need to have their inputs tied down or do they do it internally?
    Last edited: Jul 8, 2016
  2. dannyf

    Well-Known Member

    Sep 13, 2015
    the pull-up will have current through it, especially through the probe. You can check the datasheet on that.

    The easiest is to enable the pull-up, measure the voltage on A0, and then turn off the pull-up.

    The best solution is to put the mcu to sleep most of the time and wake it up periodically to measure the resistance, on an AVR (=arduino without the external circuitry).
    camjerlams likes this.