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Discussion in 'Electronic Basics' started by lerameur, Jan 30, 2007.

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  1. lerameur

    lerameur Guest


    I am building a robot and wanted to have isaltion between the
    microcontroller and the motor. So Iknow have two batteries (one for
    each) . I aslo want to have a voltage checker for each battery.
    Because the reference value is not present when I calculate the
    voltage on the motor battery I am not able to determine the voltage.
    I am using a A/D conversion, but seen from the microcontroller , the
    motor battery is floating. (no good)
    I thought of using an opto coupler but some advise me not to because
    they are non linear. I looked for some isolation amplifier, but these
    chip are very expensive. Any alternative I could use that could give
    me a fair reading ?


  2. Noway2

    Noway2 Guest

    Take a look at instrumentation and difference amplifiers. Analog
    Devices has a pretty good website. I believe that both types of amps
    can give you a pretty high degree of isolation when used properly. This
    is especially true of the instrumentation amps, but I also think that
    they are usually designed with a high gain, so they may or may not work
    for your application.
  3. default

    default Guest

    You could still use a simple optical coupler - just calibrate against
    a lookup table in memory.

    If the two batteries can share a common ground there's no problem.

    If they have to be separated - ask yourself why you need isolation?

    Just to keep the motor supply from talking to the data supply? If
    that's the case you can use a high impedance op amp (something like a
    Jfet input amp) and use relatively high series resistance into the
    differential inputs - it won't be "isolated" strictly speaking, but no
    significant current will be exchanged by the two systems, and no

    A cheap and dirty isolation trick is to use something like a two pole
    double throw relay and charge a cap with the motor voltage then switch
    the relay and read the voltage on the cap.

    Another technique is to use a voltage to frequency converter on the
    motor side to send a string of pulses over to an optical coupler whose
    frequency is proportional to the motor voltage. You read the
    frequency at the micro controller and calculate the voltage or convert
    the pulse train back to a voltage level with a frequency to voltage
  4. John Fields

    John Fields Guest

    Flying capacitor input to the ADC: (View in Courier)

    +----------->\ <--------[ADC]--->DATA
    | \ |
    | O |
    | | |
    | | |
    | O |
    | / |
    +----------->/ <----------+----GND
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