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Advice please: controlling a transistorised relay board with anopen collector output

Discussion in 'Electronic Basics' started by Frank Sweeting, Nov 29, 2004.

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  1. Hi,
    I'm not up with modern electronics & I'm struggling a bit with this: if
    anyone can give me any advice or suggestions I'd be grateful

    I have a device with an open collector output which can be controlled ON/OFF
    remotely by phone. I'm told I have to be careful about the amount of current
    supplied by the open collector output so I chose to use the open collector
    output to switch a relay with a transistorized relay board to trigger its

    I've got a 1.5k resistor between 12V on the device & its open collector
    output, the output then goes to the trigger on a relay board. When the
    output is ON theres 10.5V on the trigger, & when its OFF theres 0.7V on the

    Powering up the device has the open collector output ON & the relay is
    triggered ON, BUT, when I command the Open collector OFF the trigger
    voltage only drops to 0.7V, & the relay stays ON
    So I haven't got control of the relay as I wanted because I cant turn it

    I've experimented & found I have to get the trigger voltage down to about
    0.1V before the relay goes OFF

    So heres the question, how can I get the open collector output down to 0.1V
    or if I can't is there a work around

    TIA Frank
    Frank Sweeting

  2. Active8

    Active8 Guest

    You don't need any. Try a 2k pull up.
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