I want to use my electric door bell to trigger a wireless door bell. I replaced the transmit button of the wireless transmitter by a relay and connected it parallel to the speaker of the electric doorbell. When the doorbell is pressed, the relay switches. This works fine.

However, the outside button implements a light, so there's always a small current in the circuit, enough to keep the relay closed once it is triggered. In other words, my Wireless door bell keeps transmitting also after releasing the doorbell, as long as it has been triggered once. What can I do to resolve this problem?


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ This circuit diagram makes no sense to me. \$\endgroup\$ Jan 17, 2015 at 21:18
  • \$\begingroup\$ The question makes no sense to me \$\endgroup\$
    – Andy aka
    Jan 17, 2015 at 21:59
  • \$\begingroup\$ Is the 1 MHz value in the signal source correct (it's not audible)? As I understand SW2 is the outside button. When it is pressed the speaker plays the signal source sound and it operates the relay that simulates a button press of the wirelessdoor transmitter \$\endgroup\$
    – Roger C.
    Jan 17, 2015 at 22:14
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    \$\begingroup\$ Both the question and the diagram make sense if you think about how a typical doorbell works - you have an AC line, a step down transformer, and an electromagnetic annunciator understandably (mis)represented by the speaker. In actuality, such a circuit taken literally would generate a load 50/60hz hum if the speaker coil impedance was high enough not to blow when subjected to the transformer output. One could also draw another relay interrupting its own coil power as an annunciator, but that's implementation detail irrelevant to the question actually being asked. \$\endgroup\$ Jan 17, 2015 at 22:39
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    \$\begingroup\$ Where's the lamp in the circuit? Across SW2? What are the specs for the lamp and the relay? \$\endgroup\$
    – tcrosley
    Jan 18, 2015 at 0:22

2 Answers 2


You might put a resistor in series with the relay coil. Choosing the resistor value is tricky without measuring what is going on. A possible way of finding a suitable value is to keep adding series resistors of 10 Ohms until it is not able to trigger, and then remove the last resistor.


Place the lamp across the power source, ballasted if need be. It'll be on 24-7, but most illuminated doorbell buttons are.


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