Turn on a led with RC filter

Discussion in 'The Projects Forum' started by bisto, Nov 5, 2015.

  1. bisto

    Thread Starter New Member

    Oct 15, 2015
    1
    0
    Hi I'm italian. I have a project to do: I want to turn on a LED only if the frequency in input is less than 100hz (for example).
    I can only use RC filter.
    Thanks for your help!!
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    any chips you can use like phase locked loop (pll) or op amps?
     
  3. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Italians can only use R's and C's?
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    there is no resonant point with rc circuits like lc circuits. you have to have active elements and use the phase shift of the rc circuit or several rc circuits across an active element to use to detect frequencies. see "ACTIVE FILTERS".
     
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