Christmas Tree

v3.1

This is a simple design that blinks a set of LEDs in a christmas tree pattern. A blinky christmas tree circuit isn't very impressive in terms of electronics but I've found that it makes a good present for people who aren't into electronics (i.e. relatives). I made the original version of this design as a christmas present for my girlfriend. The first version was made on proto board and was a nightmare to solder together.

Front view of original christmas tree circuit built on prototyping board (using a LM556 timer)

Rear view of original christmas tree circuit showing a tangled mess of point to point soldering

This was the first and last complete prototype that I made on proto board. This style of prototyping produces circuits that are very difficult to understand, debug, and modify. Because of all the extra work involved they also take forever to assemble. Suddenly I became very interested in designing and fabricating custom pcbs. An early v1.2 design of this circuit was the first pcb that I managed to etch (using the ferric chloride etching system)

First pcb that I etched - a v1.2 design of this christmas tree circuit. The ground plane was removed in later designs to prevent shorts from soldering and incomplete etching

The circuit is based on a LMC555 timer which activates a transistor switch to blink the LEDs at about 1Hz. It can be configured to operate from 5V or 9V supplies by switching a few resistors. This allows it to be powered with USB (5V), a 9V battery, or an AC adapter (using 2.1mm jack or header connections). Wires were routed on the bottom of the board where possible so it can be built as a single layer board with one jumper wire.

A more recent design shows a lot of improvements from early versions in terms of simplicity, reliability, ease of assembly, and decreased size

Front view of a recent christmas tree circuit (v3.0) operating from an AC adapter with LEDs on

Rear view of a recent christmas tree circuit (v3.0) showing simplified pcb layout and surface mount LMC555 timer


Eagle Design Files

Cadsoft Eagle pcb schematic [ .PNG | .SCH ]

Cadsoft Eagle pcb layout [ .PNG | .BRD ]

References

  1. LMC555 timer datasheet