Tuesday, December 4, 2007


I put together a simple AVR-based device to stand in for the tried-and-true pumpkin candle this year. It uses two high-output (12,000 mcd) white LED's driven (a little too hard) by a regulated 5v supply that's shared with an ATtiny13v. All of this runs off of a 9v battery and should last for days given the tiny amount of current it draws.

The bill of materials isn't super long, and I had everything on hand so putting it together was pretty easy. I free-formed the first one, wrote the AVR Studio assembly code, then went back and made a proper schematic and built the second one. The first one is a lot uglier than the second due to all the rework and the extra wiring for the ISP connection.

C1 10uF
C2 100uF
LED1 High output white 5mm
LED2 High output white 5mm
R1 150
R2 470
R3 120
R4 120
R5 10k This is a 10k for a pull-up on the RESET pin
S1 Small SPDT sliding switch
T1 2N3904 Any small signal transistor will do
T2 2N3904 I used the 2N3904 because I have a big bag of them

Here are all of the materials required, assembled in marching order:

Here's the schematic:


Here's the finished product (the second one... after I knew what I was doing. My layout still sucks, but it all fits and is fairly orderly.)


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