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Current measurement using 50mV shunt and AVR microcontroller ADC

Discussion in 'General Electronics' started by jim, Nov 28, 2005.

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  1. jim

    jim Guest

    I want to build a little device that will measure current flow to/from my
    deep cycle batteries. I want this use a microcontroller to provide data
    collection etc. The currents involved will be 0-30amps, either direction (
    load and charging).

    I seems to me that the 50mV from the shunt is far too low a value to
    measure directly with the AVR's ADC, not to mention the problem of the
    "negative voltage" on the shunt with the battery is being recharged (and
    yes, I do want to measure charge current as well.

    The entire device will be powered by the battery system itself, using 7805
    (or some similar 5V regulator) to supply Vcc for the AVR.

    I'm guessing I'll need to use some sort of opamp circuit to scale the
    -50mV-to-+50mV raw input to something like 0-2.56 volts to be read by the

    My question is... how do I do this.. I'm more of a digital type so I'm
    looking for advice on this analog project.


    - jim
  2. Iain Wilkie

    Iain Wilkie Guest

    Consider the MAX472 chip


  3. jim

    jim Guest

    Thanks... Looks interesting.
  4. Robert Baer

    Robert Baer Guest

    More Maxim / Dallas vaporware?

  5. We all know you get a hardon every time someone mentions anything
    made by Maxim. Get over it. You've cried about them for years and you
    make yourself look like a fool.
  6. Robert Baer

    Robert Baer Guest

    Do tell.
    I have talked to a number of reps that quit handling Maxim due to the
    sever problems of part availability.
    Add that to the number of times i tried to get parts..even two for
    eval - and there were zilch.
    Perhaps you should make them sole source for all ICs...

  7. Maxim was about 20% of our IC usage and we never had any problems
    with buying production quantities from them. I have never had any
    problems getting any samples from them, or any data I needed. In fact,
    the first time I contacted them directly they sent me a copy of every
    databook they had in print after Pioneer failed to send me some
    photocopies I requested, and didn't tell me about Maxim's samples
    policy. In fact, Pioneer screwed me on the prices and took months to
    get the parts. Maxim sent me the samples in three days. I no longer
    deal with Pioneer in Orlando.

    In case you don't know, they are either second sourced, or are second
    source on a number of parts.
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