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HELP Issue triggering door bell with relay circuit

Discussion in 'Electronic Design' started by [email protected], Jun 25, 2013.

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  1. Guest


    So I have put together the following circuit found in the link and everything with the regular part of the circuit namely, lights, switches, lock-out function all work.

    I have wired up a common house-hold door bell which comes with it's own transformer to step down the voltage. And, I'm supplying power via it's own ACcord wired within a project both separate from the Game Show circuit. I'm using the small relay circuit to act as the door bell button.

    Problem is it seems as though the capacitor maybe too large and is not discharging fast enough.

    What I'm seeing after I press one of the game show switches is the corresponding light coming on, but with a slight delay the bell rings. However I'venoticed a hum coming from the bell unit when powered and connected to the relay circuit. It appears that piece that hits the bell plate is holding and then heating up when plugged in for a bit of time.

    Can going from a 1000 uF capacitor to perhaps a 500 or 250uF help solve thedelay, the sticking of the bell striker? Any help would be greatly appreciated, I'm sooo close to finishing and this is the only detail holding me up..


  2. Sylvia Else

    Sylvia Else Guest

    When the relay isn't energised, the bell should be completely
    disconnected. I'd have to wonder whether the relay is defective.

    I'm a bit suspicious of the way the relay is controlled - a slowly
    reducing coil current doesn't seem very nice.

  3. Guest

    Hello Sylvia,

    I tried to follow the circuit as it was laid out. What would you suggest for this setup? Should I replace the relay? It just acts weird, at one point when I would press one of the buttons it triggered multiple lamps as thoughvoltage was feeding back in to the circuit via the relay. Once the bell system was disconnected it worked normally.
  4. Sylvia Else

    Sylvia Else Guest

    You could check the diode connected across the relay coil, and that it's
    really connected to the rest of the circuit (it may look as if it is,
    but dry joints can be deceptive).

    Beyond that, I'm afraid to say that I find the entire circuit
    questionable. It quite needlessly uses dangerous voltages, which among
    other things makes it more difficult to diagnose circuit faults.

  5. Jasen Betts

    Jasen Betts Guest

    100ohms and 1000uF should give a pulse on the relay well under 1
    second in duration

    so the gong solenoid should spend most of its time unpowered and not
    heat up noticably,

    perhaps you've got the normally closed relay contacts in the gong circuit
    instead of the normally open relay contacts.
  6. Geo

    Geo Guest

    I would agree since the OP said:-
    "What I'm seeing after I press one of the game show switches is the
    corresponding light coming on, but with a slight delay the bell

    So it does a ding after the delay.
  7. Guest

    Yes, it lights a bulb after the button press, then the bell dings like a second later. But it seems as though the striker stays stuck for a bit longerpast that. I plan to purchase a 220 uF capacitor since it doesn't need a longer power time and recheck the connections to my relay.
  8. whit3rd

    whit3rd Guest

    Unless I'm mistaken, the capacitor will see rather high DC voltage, I hopeit's rated
    for a hundred or two hundred volts. The parallel resistor (51 ohms) is the only reason
    it doesn't get nearly full rectified 120VAC (about 170 VDC).
    If you want a single 'ding' of the bell, it's usually better to trickle-charge a capacitor then
    switch it onto the load; I'd implement this with a capacitor+zener to make a low-ripple
    DC supply, and a '555 configured as a one-shot.
  9. Guest


    Thanks to all who offered their valuable advice and knowledge. The project is complete and working great!!! I found that the door bell was wired to the NC instead of NO, I misinterpreted the layout on the back of the baggie. Also, I found that there was a bad diode in relay portion of the circuit. Replaced the diode, and connected to the NO, no need to step down the size of the capacitor.

    Thanks Again!!

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