A noisy output...

Discussion in 'General Electronics Chat' started by ScorpFire, Jan 1, 2010.

  1. ScorpFire

    Thread Starter Member

    Jun 4, 2009
    13
    0
    I have a modem which has a (0v when low, 2.8v when high) digital output.

    I have a an external relay module that i want to control with this output. Basically turn on the relay when the output is high.

    However i see that whenever i turn my modem output to high, the relay produces a buzzing sound instead. The contacts do not close. I suspect that the signal may be noisy, is there any way to reduce the noise? perhaps with capacitors or something.

    Here is my circuit:

    [​IMG]
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    It can be that the voltage on C1 is not stable.
    Change it to 1000 uF / 25 Volts for a try.
    The voltage on C1 will be around 15 volts as you use a 12 volts AC.

    Greetings,
    Bertus
     
  3. Paulo540

    Member

    Nov 23, 2009
    188
    0
    If the ripple isn't sufficiently filtered out, the relay won't fully 'kick over' because the voltage is dropping below the minimum pull-in. every pulse.

    As bertus mentioned, you need a bigger cap, based on the current the relays will be drawing.
     
  4. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Do you have a scope? If so look at the modem output to make sure it is dc. If not use a blocking cap and meaure the output voltage with an ac meter. Also check the power supply voltage for the relay, it should be 90% dc.
     
  5. ScorpFire

    Thread Starter Member

    Jun 4, 2009
    13
    0
    Output is dc ive checked it...maybe yeah the 12v is not stable,

    will try....thanks for the help
     
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