Introduction: Build the BandBlinker - 120v Audio Trigger on the Cheap.
To help compliment the BandBlinder, a cheap but good working stage light kit for a friend's band, I've also created the BandBlinker, an audio trigger for the light kit made with inexpensive, easy to find parts.
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Step 1: Gather Materials
The materials for this audio trigger should be pretty easy to source. Radio Shack, a hardware store, and an auto parts store should have everything you need between them. The materials you need are as follows:
1x sound triggered car effects light with adjustment dial
1x shallow "new work" wall gang box
1x three prong wall outlet
1x wall outlet cover plate
1x 12v relay (the higher the amperage it can handle the better off you'll be)
1x project box (to hold control circuit)
1x computer power cord (the thicker its wire the better)
1x 12v AC adapter
knife/ dremel (to work cases and open the light)
Step 2: Deciphering the Light Controller
To get the trigger you need for the later steps, you must first figure out where you're triggering line on the effects light is. First use the knife or dremel to remove the back of the case which holds the circuit board for the light. *BE CAREFUL* the light itself is powered by a high voltage transformer that steps up the 12v the light is fed to what is probably a few thousand volts.
That being said, hook the light's power wires to the lines coming from the 12v AC adapter, making sure you can make the light function as it's meant to, usually with a normally on, and variable sensetivity audio triggered mode.
Now get your multimeter, set the light to a sensetivity that you can trigger it with your voice, and probe for a spot on the board (probably somewhere near the middle) that is at 12v when the light is on, and 0v when the light's off. these two points are what you will attach the coil of the relay to later on. You may want to mark them for later reference. Different brands of lights will likely have different boards, but the concept of how they work should be similar enough for our purposes.
Step 3: Much Bashing and Breaking
Now it's time to have a little destructive fun. disconnect the AC adapter from the wall, and excise the board that lives inside it. We want the board out of it's "wall wart" case so that it can be more easily fit into our project box later on. I've done this many times, and the easiest way i know is to cut the wire off as close to the case of the AC adapter as you can, push the rest of the rubber stress relief into the case, then use needle nose plyers to tear chunks of plastic off until you're able to get the board out. Try to work along the seam of the case. Be careful to not hit or otherwise damage things inside the wall wart as the temptation to hit it with a hammer becomes intoxicating depending on how well the adapter you're gutting is glued together.
Alternatively, you could also just add a barrel plug to your project box and use the adapter as is, but it's not as slick if you have to use two outlets to power this box now is it?
Now that you have the power source for your light's board laid bare, you'll want to do the same for the control board in your light as well. pull the board out of it's case, keeping about 6" of the the 12v power cord on, but cutting or desoldering the lines that feed the tube of the light itself. these are those high voltage ones we talked about earlier, and you want to make those as small a target for finger touching as possible.
Step 4: Connect the Bits and Bobs
Now that you have all your materials thoughrougly torn to bits, it's time to put them together how we want them. Below is a block diagram of how my trigger box is wired. Feel free to ask me any questions in the comments section about it. Basically the AC adapter powers the control board, which triggers the relay when sound is loud enough, activating the relay and the power to the outlet. The lines between your relay and control board are the ones you metered out and marked in the previous steps.
Step 5: Testing and Assembly
Now would be a good time to test the whole circuit with a desk lamp to make sure it works as it should.
Once you're happy with how it works, you can start putting it in the casing. For mine, I melted a hole in the case for the adjustment dial to stick out of, made a hole for the power cable to sit in (knot the power cable so it won't come out), and made a notch for the wires feeding the outlet to exit the project box from. I then mounted the outlet in the gang box, added it's cover plate, and super glued the gang box to the project box so that if I need to I can take the screws of the box off and get to the insides again. I also glued the boards and relays into the project box so they don't go anywhere.
Step 6: Completion and Usage
Once everything is complete, you can test the whole thing again, adjusting the dial to the volume you want it to go off at. You can hear the clicking of the relay inside, which makes for a neat sound and feel if you hold the box as it's doing it's thing. Putting the whole control box near the source of audio you'd like is a good idea, but if the amp is too loud, moving it away or putting it in something that insulates sound might be a good idea (though you'll want to make sure you don't have it overheating or shorting out since sound insulators are usually good heat insulators as well.)
Other than that, You just need to hook the BandBlinker up to your BandBlinder or even a desk lamp or other light and rock away. Hope you found this instructable helpful.