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Relay driver

Discussion in 'General Electronics Discussion' started by Tailchaser, Sep 13, 2012.

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  1. Tailchaser

    Tailchaser

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    Sep 13, 2012
    Hi,

    I'm trying to use an old digital central heating timer to switch a set of LED's on and off at pre-set times. I'm fine with the LED side of things (drivers, etc), but am struggling with the timer side.

    The timer runs from 1.5 - 4.5 volts (with a back-up battery).

    When in off mode the "output" is 0V

    When in on mode the "output" is +0.5V (as measured with a meter)

    So, I'm guessing I need to use a transistor here to switch a realy on (with diode protetion, etc) but am struggling with the configuration, bias resistors, etc. The realy coil is 3V DC and draws about 30mA when on.

    many thanks
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi tailchaser

    It would be a bit suprising if the timer put out a small voltage like that
    I would have more expected the timer to have a set of relay contacts

    can you do a sharp pic of the timer showing its connections please

    Dave
     
  3. Tailchaser

    Tailchaser

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    Sep 13, 2012
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    hi Jeff

    well the datasheet states that it comes in 2 versions relay output and CMOS
    so does it state in YOUR relay which version it is ?

    Dave
     
  5. Tailchaser

    Tailchaser

    3
    0
    Sep 13, 2012
    Hi Dave,

    Mine is the "CMOS" version i.e NO relay. If it were the realy version, then I wouldn't have an issues as I could use that to switch the load.

    Jeff
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    It is possible to make a circuit that will switch a relay based on a signal that swings from 0V to +0.5V but I doubt that's the proper voltage. There is no reason for a microcontroller that's running at 1.5~4.5V to generate an output of only 0.5V, unless it has been damaged or is generating a pulse stream. Therefore I suggest you check very carefully how you're measuring the voltage, take photographs of the measurement points, and explain how you made the measurement.
     
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