Digital ammeter

Discussion in 'The Projects Forum' started by sportsfan27, Apr 18, 2009.

  1. sportsfan27

    Thread Starter Active Member

    Jan 29, 2009
    I'm looking for a schematic for a digital ammeter that doesn't output the value to a display, but to a microcontroller/transistor/something like that. Any ideas? Thanks
  2. SgtWookie


    Jul 17, 2007
    Don't have one for you offhand, but it wouldn't be too hard to make one.

    If you open up a cheap digital multimeter and take a look inside, you'll see a brass rod or bar connecting the 10A or 20A current terminal to the common terminal. Brass has roughly 4.822 times the resistance of copper. Current is measured by measuring the voltage drop across a known resistance; as Ohm's Law says: I = E/R (Current = Voltage / Resistance)

    Basically, you'd want to use a fairly low resistance for the brass bar/rod, and then amplify the voltage drop across the brass bar/rod using a precision opamp that has rail-to-rail inputs/outputs to match the current range and resulting opamp output voltage range to the ADC input range of your microcontroller (usually somewhere around 0v-4.5v or so, check the documentation for your microcontroller).