Tuesday, 9 September 2014

Mains Switch Widget for Home Automation

The Mains Switch Widget allows the user to switch 230V or 110V mains ON and OFF to mains powered devices from microcontrollers like the PIC and the Arduino or from single board computers like the Raspberry Pi and the Beaglebone. All the safety requirements are designed-in to prevent any faults resulting in a fire. A plastic enclosure is supplied to prevent the user from accidentally touching the mains voltage.

Since launching the Custard Pi range for the Raspberry Pi, we always get asked for the ability to switch mains powered devices ON and OFF from the RPi as well as other single board computers like the Beaglebobe or a micro controller like the Arduino.  I always explain that there is more to switching mains ON and OFF than just using the correct relay.

One has to take into account the following:

1.  The correct spacing on the PCB between the mains voltage side and the low voltage side

2.  Anchoring the mains cable so that they do not accidentally pull out and touch other parts - thus making them LIVE

3.  The correct fusing - to prevent a fire in case of a fault

4.  Prevent the user from accidentally touching the PCB with mains voltages on it

All this is taken care of on the Mains Switch Widget. It is supplied in kit form and the user supplies the appropriate mains plug and socket based on the country where the appliance is going to be used.


The Mains Switch Widget has the following features:

*    Supplied with a plastic enclosure to protect the user from shock
*    Electrical isolation between the control side and the mains voltage
*    Protected by a 5A fuse in the product
*    Cable ties to prevent the mains cable pulling out
*    LED indication of ON and OFF states
*    Detachable input connector
*    Can be configured for most parts of the world by using a suitable mains extension lead (not supplied).

More information and full documentation available here.

This widget is supplied in kit form. Moderate skills are required to solder the components and assemble the kit. As this Widget uses mains voltages great care has to be taken during the assembly. For this reason, this kit is designed for use by competent persons.

Tools required to complete the assembly are shown below.


There are many applications that require switching mains powered appliances ON and OFF. Here are some examples.

Maintaining an environment at a constant temperature:
A temperature measuring device and the Mains Switch Widget with a heater could be used in a feedback control system to maintain a constant temperature.

Keeping a water tank topped up:
A water level detector can be used to control a pump using the Mains Switch Widget to maintain constant water level in a tank.

As a module in a Home Automation system:
A Raspberry Pi could be used to switch lights, heating and ventilation using this product. With a browser interface, this could be controlled from anywhere in the world. 

In summary, the Mains Switch Widget allows hobbyists to control a wide variety of mains powered equipment under micro-control using a simple voltage control.

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