Home Automation With a Clap Activated Mains Device

By Robin Mitchell


Home automation is an industry that is still in its infancy. While there are some clever devices that can control your lights and curtains, the majority still prefer the old fashion method of Do It Yourself. However, it won’t be long before home automation takes over, so in this project, we will build a “clap-activated” mains device!



Warning: This device deals with mains electricity and is shown as a demonstration only. Those who wish to attempt such a project involving the mains should be certified to do so and understand the dangers of working with high voltages.


Required Materials


How Does it Work?

The circuit’s function is to take a loud sound and then turn on or off a mains device. The first part of the circuit is an electret microphone that converts sound waves into voltages. This voltage is then coupled to remove the large DC offset produced by the 10K pull-up resistor. The signal is then smoothed via R3 and C2 to turn the many peaks of a clap into a more smooth pulse and this smoother signal is then fed into an op-amp in a comparator configuration. The output of the comparator is then connected to a Schmitt trigger whose parameters are adjustable thanks to RV2 and RV1. The output is then used to toggle a 4013 flip-flop who is configured as a toggle by connecting the inverting output to the data input. This results in an output that toggles every time a loud noise is detected (i.e. from a clap).

The 4013 is used to control the state of a relay that is used to turn on and off our mains supply to our mains connected device. It is imperative that the live (sometimes called hot) wire is switched and the neutral and earth lines left connected. Such switching is important because disconnection of the neutral and earth connections can potentially leave to a circuit that will not disconnect under fault conditions (a feature found in the fuse board at your home).

The circuit demonstrated here works well with the electret microphones stocked in my workshop but if you should find that the signal from your microphone is too small then an additional amplifier can be included between C2 and the comparator to produce a larger output.

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The circuit itself can be constructed using many circuit construction techniques including PCBs, stripboard, and breadboard. However, the relay itself should only be near the control circuit if it is on a PCB and has suitable traces for handling mains voltage. If any other method that a PCB is to be used the exercise extreme caution. The control relay should not have any contacts exposed and all mains electricity parts should be located in an insulating, approved box (many project boxes work well for this). The example shown here is not how the project should be completed but has been done to demonstrate the various parts carefully. Despite not being in a safe enclosure, the demonstrated project shows a dedicated socket outlet and plug inlet that connects to the mains. Connections to this project should never be done with wiring directly taking a feed from the house wiring (they should use appropriate plugs into sockets).


The demonstrated projects

The main circuit



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