I am creating a buzzer driver that turns on when the output of an AND gate goes HIGH. What I would like to create is some way to shut off the signal to the buzzer by opening an SPST switch, but the switch must be able to return to the original closed state after a time delay so the AND gate can drive the buzzer again in the future.

I thought about creating an RC network to create the delay but I don't know how to implement a switch that after it is opened, closes again on its own after a certain amount of time. Ideas?

  • 1
    \$\begingroup\$ So, you want a re-triggerable one-shot kind of device? How much current does the buzzer require? What voltage does the buzzer operate on? \$\endgroup\$
    – jonk
    Apr 18, 2019 at 22:19

2 Answers 2


To add specifics to Dwayne's answer, a simple SPDT relay will do the trick.


simulate this circuit – Schematic created using CircuitLab

Each time the alarm condition occurs, the buzzer sounds until the "Silence" button is pressed. Then the relay pulls in and stays that way until the alarm condition goes away.

  • \$\begingroup\$ Is there any documentation or any links you can recommend so I can understand exactly the why it would behave that way? I'd like to understand the circuit you provide instead of just copying it. I have never worked with relays so I don't understand how the SPDT would return to it's original Normally Closed state when the Common stops receiving a High signal. \$\endgroup\$
    – AnthonyBB
    Apr 19, 2019 at 0:51
  • \$\begingroup\$ Actually, I think I got it. In normal operation the Alarm signal would power the buzzer, but when the Silence button is pressed, that same signal will provide current that will power the relay coil, pulling the relay switch in the Normally Open position. Since the Silence button is only momentarily pressed, the Alarm signal now powers the relay coil, maintaining the position of the relay switch in the Normally Open position and there is no path to the buzzer. Once the Alarm signal goes off, there is nothing powering the coil so the relay goes back to the original position. Correct? @dave-tweed \$\endgroup\$
    – AnthonyBB
    Apr 19, 2019 at 1:25
  • \$\begingroup\$ Yes, correct. Let me make a slight adjustment to the schematic. \$\endgroup\$
    – Dave Tweed
    Apr 19, 2019 at 4:12

The standard method of dealing with alarm noise-makers is to have a "Silence" push-button. Pressing the button causes a circuit to latch and disable the noise-maker.

The circuit automatically returns to normal when the condition causing the alarm is cleared. This allows the noise-maker to be operational again when the next alarm occurs.

It is rare that the silence duration is based on time rather than the source of the alarm signal being cleared but sometimes that is required. In those cases, the silence circuit is also (normally) reset to normal should the source of the alarm be cleared before the silence time period has elapsed.


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