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high pass filter

Discussion in 'Electrical Engineering' started by gis, Oct 5, 2003.

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  1. gis

    gis Guest


    I am trying to build a circuit for detecting a visible light source (such as
    red LED). I am using a phototransistor, and want to filter out all ambient
    light (cieling lights, etc..)... anyone know how to construct a High Pass
    filter to do this? say cut out the 60 hz room lights

  2. Gene

    Gene Guest

    You must power the LED with a relatively high frequency (1-10Khz), so
    that you can extract from the phototransistor signal the frequency
    component belonging to the light originated by the LED and reject all
    the spurious components (60, 120, etc. Hz). For this you need a bandpass
    filter. You must also make sure that the spurious light impinging on the
    phototransistor doesn't saturate its output.
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