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Producing 0-10v dc using 0-10r FSR resistor strip

Discussion in 'Power Electronics' started by Cloudhop, Nov 26, 2017.

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  1. Cloudhop

    Cloudhop

    5
    0
    Nov 26, 2017
    Im wanting to add velocity and aftertouch to a keyboard that controls a modular synthesiser by using FSR strip under the piano keys.
    The FSR only produces 0-10 ohms variable and I need to convert that into 0-10 v dc variable for the actual control voltage and with little or no latency.

    How would I go about tackling this ?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Welcome to EP.

    You could drive the strip with a constant current of 1 A. By application of Ohm's law in the form V=I*R you get 0 V...10 V.

    Just kidding. While this in principle works, it is not feasible. The strip would dissipate up to 10 W as waste heat. Use the strip as part of a variable voltage divider instead and amplify the output to the required range:
    upload_2017-11-26_19-4-25.png
    Some notes here: You'll have to use a rail-to-rail opamp to get down to 0 V output voltage. Or use a dual supply.
    R4 at 8,17 kΩ is not available off the shelf. The nearest standard value is 8.06 kΩ or 8.25 kΩ. If that results in too inaccurate an output voltage, replace R4 by e.g. a 7.5 kΩ fixed resistor in series with a 1 kΩ potentiometer to adjust the gain for the required match of the output voltage to the strip's resistance.
     
  3. Cloudhop

    Cloudhop

    5
    0
    Nov 26, 2017
    Harald

    This is so kind of you to give me this circuit. In my limited electronic theory I see how it works ...thank you so much, I really appreciate your help and time.
    This is a very good forum, I wish I had come to it months ago!
     
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