Picture of Electronic Candle Noisemaker
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.
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Step 1: Materials

Picture of 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
Heatshrink tubing

Step 2: Open the candles

Picture of 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

Picture of 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.
I have done something similar to this, i.e. using a light sensitive transducer, specifically a small piece of silicon solar cell,  to listen to the signal of a flickering light - as sound.  Here:

The amplifier module helps a lot.  With the setup I am using there is no need to put the light source and sensor in intimate contact inside a light tight box.  Just a few cm of distance between the light source and the sensor is usually close enough to get a clear, audible, signal.
Fenwick3 years ago
Those candle things look really fun to take apart and experiment with.

The fact that they all produce different tones makes me suspect that they have a lot of analog circuitry to them. I'm gonna try and pick some up tomorrow and see what they've got inside them.
Fenwick Fenwick3 years ago
Okay, it turns out all the circuitry in mine was All inside the LED, so I couldn't get at it and take a signal at all.
noahh (author)  Fenwick3 years ago
I don't know how well you read the tutorial, but mine was just the LED and a battery. You get the sound by attaching a photocell to it. It's all in the instructable.
Fenwick noahh3 years ago
I read how you did it, I was just trying to figure out if there was another way, or anything that could be done to modify the electronics that generate the pulses.
nof-z3 years ago
pretty cool