The basic Idea was to have Christmas lights flash with the music. In my design I used an ordinary amplified computer speaker, a diode bridge, and a 'CRYDOM' SSR (Solid State Relay). In order to increase the time that the lights were on as well as protect the SSR I used a Diode Bridge to rectify the signal from the amplifier circuit.
Things that you will need:
1. Solid State Relay
2. 4 diodes
3. Computer speakers (or some sort of audio amplifier)
5. AC Outlet
6. Various wires
Large Hammer (very important)
Step 1: Finding a Solid State Relay
Any SSR can be used as long as it is rated for 120VAC or greater and the correct amount of current. A standard strand of 100 Christmas lights is ~0.5 amps. To be on the safe side if you only wanted to run two strands of 100 lights you should probably use a SSR rated at ~2 amps (more is always better in this case).
Something else to keep in mind is the input voltage range. 2-32 VDC is the most popular range (I find that this range works best).
Step 2: Review Circuit (DO NOT SKIP!)
Most speakers are not strong enough to trigger the relay by alone. For mine to work I actually had to connect the input of the speaker to the output of a stereo. Refer to images for details on how this was done.
You would not believe how many emails I get asking why it is not working because this step was skipped. There is another instructable that is based on my design that does not include this step.
Note: If the stereo is turned up too loud it could fry the computer speaker amp (it is not designed to be used like this)
Step 3: Assembly
This is one of those adapters that reduce the three pronged plug to a two prong plug. I was looking at one of these and noticed how there is a threaded hole in the center, perfect for mounting it to things. I dremeled notches in the top of the speaker case so that the prongs could fit through (you could use a knife, but be careful). I then mounted it to the case using a screw. I used this instead of a normal outlet because it is small, requires minimal cutting to install and is cheap (around 20 cents).