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Peter Bailey's RF-Controlled 'Smart' Socket Arduino Project

Gareth Halfacree

Peter Bailey's smart socket transmitter

Many applications of 'smart' devices revolve around controlling the flow of power to an existing home appliance. From internet-connected light switches to devices like Google's Nest thermostat, it's a popular market - but one that the beginning hobbyist may shy away from thanks to perfectly-understandable concerns regarding trial-and-error engineering mixing poorly with 240V AC electricity supplies.

Developer Peter Bailey has come up with a neat workaround for these concerns, however: build an Arduino-powered RF transmitter which communicates with a cheap, off-the-shelf remote-controlled passthrough mains relay. The result: the ability to control an attached mains-powered device through any interaction you can sense, but without the risks associated with wiring things directly into the mains supply itself.

Peter's particular implementation is relatively simple: an RF transmitter, operating in the same 433MHz frequency band as the pass-through relay, was used to capture the signal from the supplied remote control and store it for replay. When an infra-red motion sensor connected to the Arduino is triggered and a light-dependent resistor (LDR) confirms that the room is dark the signal is transmitted, picked up by the socket, and the connected device - in this case a lamp - is switched on.

Using the same simple approach as Peter, it would be possible to control any of a number of mains-powered devices using input from various sensors. A temperature or humidity sensor could be used to switch a cheap electric heater on and off, for example; when combined with a Bluetooth, Wi-Fi or Ethernet transceiver, the socket could be linked to a smartphone, tablet, or computer - turning the cheap remote-control socket into the equivalent of a far more costly 'smart' device.

A remote control light was a really good idea when I bought the RF plug sockets. But having to fumble around finding the remote in a dark room was annoying and dangerous (once knocked over a glass of water onto a power outlet). So I decided to hack it and connect a motion sensor. Here’s how I did it.

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