"Smoothing" Rsense analog input to read BRUSHED DC MOTOR current

Discussion in 'Analog & Mixed-Signal Design' started by LE-BU, Aug 21, 2018.

  1. LE-BU

    Thread Starter New Member

    Nov 3, 2017
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    Hello evrybody,
    I would like measure the image of the current of a brushed dc motor with the analog input of a MSP430 but the signal is noisy because of the brushes commutation . I don't need a realy flat signal because I will do an average with multiple sampling , but I need something more clean. Could you give me some advices about the capacitor value or the RC filter to put in place . I don't know realy how implant this filter.
    Regards My H bridge.JPG Continous DC Motor signal.JPG
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Depending in how fast you want to see changes in the current, you could use a low-pass filter on the current signal.

    Bertus
     
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  3. LE-BU

    Thread Starter New Member

    Nov 3, 2017
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    betwin 30 to 50 ms , more rapidely , it's not necessery, but have you some advise about the low pass filter calculation ?
     
  4. bertus

    Administrator

    Apr 5, 2008
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  5. LE-BU

    Thread Starter New Member

    Nov 3, 2017
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  6. crutschow

    Expert

    Mar 14, 2008
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    If a single-pole RC filter does not reduce the noise sufficiently then you may need to use an active filter with more poles such as this 3-pole, low-pass active filter.
    You would probably want to use the Bessel type for your requirements, since it has little overshoot with a step (fast changing) input.
     
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