A while ago I read on Get LoFi that you can "listen" to an electronic flickering candle by attaching a speaker to the LED. I decided to try this, so I went out and bought two packs of electronic flickering candles. Just attaching a speaker to the candle did not do anything but short it out, but I realized I could make a photocoupler by putting a photocell in front of the flickering LED. By doing to this to two (or more) candles and attaching them all to an output jack, it's pretty easy to make a cool electronic noisemaker. Each candle (even ones of the same make) is slightly different, so you will get different sounds from all of them.
Step 1: Materials
You will need:
Electronic flickering candles, about $3 each from a hardware or department store
Photocells, one per candle
Toggle switches, one per candle plus one for power
Nine volt battery and holder
Speaker or output jack
Alligator clips, for testing
Enclosure, I used a junction box
Step 2: Open the Candles
If you remove the battery from the candle, there should be two screws. Remove these and the electronics will slip out.
Step 3: Test the Circuit
The circuit is actually pretty simple. Basically, the battery is hooked up to the speaker or output jack (I started with a speaker but switched to an output jack due to low volume on the speaker) with a photocell interrupting the negative wire. The photocell is then attached to the LED by means of heatshrink tubing. Slip a small piece of heatshrink over the LED and place the photocell, face down on the LED. Use a lighter or heat gun to shrink the heatshrink. Put the circuit together with alligator clips. Each candle is made with the exact same circuit and attached to the same output jack or speaker and battery.
During troubleshooting, I noticed I could only hear the sound clearly if my finger was bridging the output jack's two contacts, so I added a potentiometer at near full resistance between the contacts.
Step 4: Solder Together the Circuit
Solder all the connections you laid out earlier. Cut one of the wire on the battery holder and solder on a toggle switch. Cut a lead to each LED and install toggles there, too. These are your power switches.
Step 5: Case Closed!
Mount everything on your case. I use a small drill bit then use a tapered bore
(pricey, but worth it) to enlarge the drilled hole until the component fits. Use pliers, wenches or socket drivers to tighten the mounting hardware.
Step 6: Going Further
This could be expanded in unlimited ways. You could add more candles to increase the number of sounds possible., you could add momentary pushbuttons to trigger the sound in short bursts, you could mount an LED on the case to flicker with the sound, the possibilities are endless! If you try this, let me know how it went and post pictures!