I²C-homebus: Switch power outlets with your PC 2

Published:2011/8/16 6:14:00 Author:Amy From:SeekIC

Paul Goossens

Construction

The printed circuit board designed for the circuit (Figure 2) has a spacious layout with all connectors carrying mains voltages conveniently located at one side. Mounting the components onto the board is not expected to cause problems. However, do pay attention to the orientation of polarized components like electrolytic capaci­tors, LEDs and ICs.



It is wise to mount the circuit into a sturdy enclosure. For guidance on aspects related to electrical safety, consult the Electrical Safety page.

The mains appliance socket fitted in the case has to be fitted separately, as the fuse shown in the circuit diagram only protects the mains transformer. Fused IEC appliance sockets are eas­ily found.

Once the board is populated, you need to check if the logic is properly isolated from the mains. This is best done by measuring the resistance between logic ground and both mains wires (Live and Neutral). Do not connect the circuit to the I2C bus until the results of these isolation tests are satisfactory.

Software

In order to enable you to get cracking with the USB/I2C interface and one or more ’device’ modules without having to do your own programming, we’ve written a small Windows pro­gram that allows module outputs to be controlled easily just using the mouse. This program not only verifies the proper operation of the hardware but also forms a good starting point for your own experiments in programming.

The main window shows an overview of selected outputs with associated names, with switches to the right of them. The setup window allows one of the connected circuits to be selected (including the test circuit with the USB/I2C interface) and subsequently add any number outputs to the ’switch list’ as well as tag them with a name. The name tags then show up in the overview seen in the main window. Both the executable program and the Delphi source code file are available free of charge from the Free Downloads section of our website.
The actual use of the modules in or around your home is left to your imag­ination and personal requirements. In any case, there should be plenty of possibilities — for a start, you could automate the coffee machine. How­ever, do make sure manual control is also possible, else your project will be depreciated (to say the least) by your housemates.

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