Analogue Inputs



  • Hi All,

    I am using a voltage sensor, link below. When connected to the Monarco the signal voltage gets pulled down. My multimeter reads the signal voltage correctly at 2.64V. But when connected back to the hat it pulls to 1V.

    Is this due to the input impedance of the AI? It seems to work ok if I rescale it though.

    https://www.geeker.co.nz/sensors/other/voltage-sensor-0-25v.html

    Cheers

    Mike



  • Hi Mike,
    the mentioned sensor is just a voltage divider. The input impedance of AI on the Monarco HAT is 4.24kOhm, which naturally changes the ratio of the divider. Therefore if the resistors are 30k and 7.5k (as per the photo) and the external voltage is 13.2 V, the AI will read 1.09 V. And yes, it will work correctly if you rescale it in software. Though you'll loose some resolution.

    The input impedance of your multimeter is probably much higher and does not affect the voltage divider that much.

    Nice example for practicing serial and parallel connections of resistors.

    Kind regards,
    Jaroslav