Solar Automation Switch Hardware

Posted on Feb 5, 2014

This is the main building block of the home automation system. My goal here was to design one circuit board that could be customized for different functions by selectively populating the board, adding daughter boards, and changing the software. Currently, this board is used to implement the functionality of a network connected light switch, a ther

Solar Automation Switch Hardware
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mostat, interfacing a keypad to the CANOpen network, and implementing basic analog and digital I/O functionality. In terms of form factor, the board is a drop-in replacement for a decora style light switch, and can be used with any decora trim plate you pick at your favorite retail store. The actual switch plate seen on the right is a 1/8" (3mm) thick piece of acrylic, which can be custom engraved if desired. Since it is translucent, you can see the status LED`s through the plate - and yes, pick any color you like. The rest of this document describes the electrical and mechanical design of the board populated as a switch The schematic below shows the essential components of the circuit, the Thermostat specific components in the red box are not populated if you are building a switch: The CPU that is used for this module is either a PIC 18F248 or 18F258. While they are pin compatible, the latter has twice the amount of memory available, and is required if you want to implement more complex software. The former is a little cheaper but will only allow you to implement the functionality of the basic switch described here. Currently, Microchip seems to be phasing out both of these chips and replacing them with the PIC 18F2480 and 18F2580. While these are supposed to be compatible with the -248 and -258, I have not tried to recompile and run any of the software for these newer chips. The CAN bus connector is a MTA type polarized...

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