Control two 120v electrical outlets with your computer


Here is one more component for "Project Everbearing" which requires the ability to toggle a 120V power source using my PC. Now there are a few interesting applications for this, home automation, music synced Christmas display, or just the nerd factor of being able to say I can turn on my coffee maker from your web enabled phone. Whatever your need, hopefully with these instructions you can do this yourself.

If we had lawyers, they probably would want us to say this:
WARNING: I am not an electrician and do not pretend to be one.  I do not know the specific building electrical codes of your area, so please be sure your wiring is completed under the proper safety code for your area. As always, using high voltage electricity can result in self-electrocution or burn down your house if not done safely so if you are not comfortable doing this wiring please contact a qualified professional.

Materials:

  • 2 – 20 amp solid state relays (got off eBay for $4.00 each)
  • 1 – Outlet box (Home Depot for $2.00)
  • 2 – 20 amp outlets (Home Depot for $1.25 each)
  • 1 – 2 outlet switch plate (Home Depot for $0.50 each)
  • 1 – PC power cable
  • 2 – LEDs (optional)

The outlet I am plugging this into is 15 amps, though my use for this project will be considerable under this but best to place for worst case scenario and I would rather trip a circuit breaker than who knows what happens when solid state relays or outlet exceeds their limits. I could have saved a couple dollars and gone with cheaper mechanical relays but solid state will last much longer even with frequent toggling on/off.

Now for the build, this was actually surprisingly easy and took less than an hour from start to finish. I first fed the power cable through and three stands of low voltage wire through access in back. I cut about 6 inches of wire off the end of the power cable. Using the continuity feature of my voltmeter I verified the hot, neutral, and ground, then checked one more time. I attached the neutral and ground in parallel to both outlets. I then connected the hot from the power cord to left side of both SSRs. I then used the 6 inches of wire I cut off to connect from left side of SSR on both and connected a wire from the left side to the corresponding outlet.

Now to add the ability to turn the things off/on using low voltage. I hooked up the wires fed through the back (which will later be hooked up to computer’s parallel port) green to positive SSR #1, red to SSR #2, and black to both grounds. Now with 3-12 volts of power to these connections will activate the SSR and provide power to the outlet. For a little added effect and easy confirmation everything is working (even with the unit unplugged) I also attached corresponding red/green LEDs that match the wires (I am getting old color coding helps) I was doing this hack indoors though first thought was to use my soldering iron to burn a nice little hole into the outlet plate but didn’t want to stink up the house, so risked using a drill instead. As you can see from the pictures I should have gone outside. With a little solder and hot glue everything seemed to be staying together.

With all the wiring completed, I carefully packed everything into the outlet box. The SSR were already pretty snug but I added little but of hot glue in case they feel like shifting around after everything was put back together. Being careful that wires are staying secure and no shorts are being created carefully screw the outlets to the outlet box. Finish it up with a (cracked) outlet plate and the assembly is complete.

Now the scariest part still remains, which is testing, first part is plugging this monster in. If you plug it into the wall and no sparks occur you are in pretty good shape but not in the clear yet. Plug something like a nightlight into your switchable outlet box, should be off now. Using a 9-volt battery connect black to (-) and red to (+) if you didn’t cross your wires anywhere the red LED should come on and appliance plugged in should get power. Now switching to the other side do the same with the green wire and appliance comes on with sparks or fires looks like a successful build.

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