NOTE: I created this my junior year in high school so it is very messy and not the best design.
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
This particular SSR does not have to be used, in fact it is a little bit overkill. The SSR I used is rated for 3 amps at 240 VAC. This 'CRYDOM' Solid State Relay is something the GE man gave me upon a visit to his lair.
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!)
READ VERY IMPORTANT:
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
I used an audio amplifier from a set of old computer speakers. They are cheap and easy to find, and best of all almost everyone has an old pair lying around. Instead of taking the amplifier out of the speaker case and finding a new enclosure to hold it all I decided to remove the speaker and put everything inside the speaker case.
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).