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Low frequency signal

  1. Apr 5, 2007 #1

    I´m new here and need a little help with some electronics.

    I have signals with information in the 0.2Hz - 5 Hz range (breath signal) with a DC offset of about 3V (not constant).
    I want to eliminate this offset voltage but still don´t change the original information.
    What type of highpass filters can I use for this application?
    How should I think?
    Information about both analog and digital filter of this type is interesting.

    Thank you!
  2. jcsd
  3. Apr 5, 2007 #2
    You just need to run the signal through a capacitor. DC voltage will be blocked and AC will run right through. For low frequencies you need more capacitance to minimize its impedance. A 1000 uF cap would do.
  4. Apr 5, 2007 #3


    User Avatar

    Staff: Mentor

    Or if you want to use a smaller capacitor, just make an opamp-based highpass filter.

    And if you can just digitize the signal, then you can write a simple digital HPF routine as you suggest to get rid of the slowly-varying DC offset.

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