Smart Switch

Monday, February 7, 2011 by darco
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I've been working on the design of my Smart Switch almost a year now, and the other day I finally received my first set of circuit boards for making my first prototype. I'm not finished populating them, but I figured I would go ahead and show it off anyway.

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The board in the upper right is the power and communications module. The board in the lower right is the load module, which in this case is a simple relay.

The board on the right is the touch sensor board. This board will eventually have a small piece of white-backed frosted glass glued to the white outline on the front of the board. This is what the user will touch to control the switch.

The board in the middle is the main board. It contains the microcontroller which controls almost all of the functions of the switch.

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All of the other circuit boards plug into the main board like this:

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More Pictures

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Safety

This is by far the most complex electronics project I've worked on to date. There are many things to take into consideration when designing such a thing, the most important of which is how to make sure it won't burn my house down if/when it fails catastrophically.

Safety is such an important issue to me that I intend to do my own ad-hoc safety testing. For a mass market device, this sort of testing would likely be done by Underwriters Laboratories. Since this device is for my own personal use (at the moment anyway), I figured that I will need to do my own testing.

Eventually I'll be destructively testing a few of these things to see how well it handles various fault conditions. I'll be building a test rig which would simulate having the switch installed in a wall while subjecting it to all sorts of abuse. This way, if it catches flame it will only burn down the test rig—and not the house.

Here are a few situations off the top of my head I would like to test while powered up and in the test rig:

  • Simulated lightning strike (need some big caps for this one)
  • Damaging impacts (enough to break the sensor board)
  • Catastrophic impacts (taking a hammer and hitting it as hard as I can)
  • Excessive vibration
  • Excessive heat, applied with a heat-gun
  • Splash with soda (with faceplate removed)
  • Excessive Humidity
  • Brown-out conditions

I haven't fully designed these tests yet, but when I do I'll document the process here.

Other notes

Embarrassingly, it seems that the finished design is just a few millimeters too tall to fit inside of a standard American outlet box. This won't be a problem for this prototype, but it means I'll need to re-design every circuit board in the switch to fit the new, shorter constraints. sigh

I probably should placed moved the 0.75µF cap under the power board instead of on top, but oh well. This is just a prototype after all.