In order to encourage us to play with electronics more,
JWA and I have begun doing monthly challenges. For our inaugural challenge, we decided upon an LED Birthday Candle. This is my entry to that challenge.
![LED Birthday Candle](http://farm3.static.flickr.com/2107/2350053369_3803998efb_m.jpg)
You blow the center pole towards one side, and the LED shuts off. To turn it back on again, blow it the other direction. It's a circuit known as
a bistable multivibrator, or "flip-flop".
I do like that it's so simple and cheap, though.
My parts list is simply:
2 - 10k ohm resistors
1 - 1k ohm resistor
1 - 220 ohm resistor
2 - 2n3904 NPN Transistors
1 - LED
3 - AAA batteries (this thing'll last forever!)
Not including the batteries, this thing costs less than 15 cents in parts. If I could work out the "blow" mechanism a little better, I think this would be a marketable product.
Okay, now for some photos:
On the breadboard:
![LED Birthday Candle](http://farm4.static.flickr.com/3181/2350875702_bb62452402_m.jpg)
Before being shoved in the pill bottle:
![LED Birthday Candle](http://farm3.static.flickr.com/2324/2350884870_d67cf9562d_m.jpg)
I had originally wanted to be able to shove this thing into a fat straw, like you get with a bubble tea, so I made it as small as possible, and soldered the pieces together straight rather than using protoboard:
![LED Birthday Candle](http://farm3.static.flickr.com/2036/2350882084_db84a59f08_m.jpg)
Next: Brighter LEDs!
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