O Christmas Tree Of Digital Logic


[Chris] over at PyroElectro is getting into the swing of the holidays with a LED Christmas tree build. Unlike the other electrical Christmas trees we’ve seen this holiday season, [Chris] designed his tree entirely with digital logic – no microcontrollers included.

The tree [Chris] constructed on a piece of perf board is a beautiful spiral arrangement of 64 green LEDs.While we’re sure getting all the LEDs soldered to the right height, [Chris] makes it look so easy to create 3D structures with circuits.

The LEDs are driven with a set of eight shift registers, themselves clocked by either a predictable 555 timer chip or a pseudo-random pattern generated with a circuit built from a few hex inverters. By setting the tree to the sequential mode, a pair of lights travel slowly down the spiral of the Christmas tree. If set to random mode, an random number of LEDs light up and walk down the array of LEDs.


9 thoughts on “O Christmas Tree Of Digital Logic

  1. I’m a bit confused by the claim that microcontrollers are not digital logic, but it’s pretty cool. I wonder if he could get rid of the last analog part (besides the clock generator) by replacing the random pulse width generator by a linear congruent PRNG using the shift registers.

  2. “While we’re sure getting all the LEDs soldered to the right height, [Chris] makes it look so easy to create 3D structures with circuits.”

    I think you may want to revise this sentence, it is very disjointed and does not seem to make much sense.

  3. Glad to see this. Just finished up some blinkenlights for a costume piece using a 555, a 4017 decade counter and a darlington array (although in hindsight, the 4017 probably could have driven everything just fine). Packaging it up into a small wearable belt pack had me thinking that a micro might be easier from a form factor perspective..

    BTW, does anyone know the reason why the pins on the 4017 are in such a random order? It makes putting them in sequential order a bit of a pain.

    1. The 4017 was originally created for a specific order from the Saudi Royal Family. Technically purchased by them, in reality it’s a purchase by the military. The pins are designed to match an existing chip so it could be a drop-in replacement part.

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