Creating a tiny digital voltmeter

Discussion in 'The Projects Forum' started by stupidlogic, Mar 18, 2011.

  1. stupidlogic

    Thread Starter Member

    Aug 10, 2010
    I did a quick search on here and didn't find much, but what I want to do is build a 3 digit digital voltmeter and make it relatively small.

    The biggest requirement of it that seems to be an issue is that it has to be powered from the source it's measuring without materially affecting the measurement. Ideally the effect of the voltmeter using the source would be less than ~50mV of the measurement.

    Everything I've seen so far needs a regulated voltage source to run the logic or MCU of the circuit and I need to somehow use the source I'm measuring to do this rather than an external source.

    APPLICATION: I want to use it to hook up to my motorcycle battery and mount the display somewhere easily accessible so that I don' have to take my bike apart to check the voltage after it's been sitting. If I can get a reliable working ckt though I'd like to use it for other applications I have in mind as well.

    Any input is appreciated!
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
  3. stupidlogic

    Thread Starter Member

    Aug 10, 2010
    Thanks. That's helpful but I am looking to build my own for experience and I can freely modify it. He packaging needs to be flatter for my applications.
  4. Markd77

    Senior Member

    Sep 7, 2009
    You can use a resistive divider, for example if you wanted to monitor a voltage that won't exceed 20V you can use a 15K resistor and a 5K resistor, which will give an output of 0-5V.
    You can use a 5V regulator from the voltage you are measuring as long as it doesn't drop too close to 5V.
    If you have a PIC programmer there is coincidentally a voltmeter in the pictures thread in Off Topic.
  5. SgtWookie


    Jul 17, 2007
    If such a circuit were left connected to a battery, the battery would become drained, which would quickly kill it.

    Making modifications to the wiring harness isn't such a good idea.

    If there is room to do so, you might consider adding a pigtail connector on your battery terminals so that you can attach an external battery float charger easily, or measure the battery voltage. Letting the bike sit idle without charging the battery for more than a week is a good way to wind up with a dead battery.

    An accurate voltmeter in a very compact size for use on a motorcycle is not really a good project for an "electronics newbie", as the environment it will have to survive in is one of the harshest on the planet. Electrical noise, shock, vibration, moisture, crud, etc. will all act to ruin your project.
  6. DickCappels


    Aug 21, 2008