Imported from GitHub: koczadly/xmas-led-controller · commit 33edb59 · license MIT

Description

Personal project to revitalise an ancient fibre optic Christmas tree using a custom-built digital LED module

README

Alrite?

Introduction

This repository contains files from a personal project. The aim was to create a small microcontroller-driven LED module to replace a broken incandescent-based fibre optic Christmas tree. This is my first project involving PIC microcontrollers, and the second PCB I've designed; mistakes and questionable design techniques are to be expected.

Files

• PCB files are in hardware (KiCad project)
• Software code is in firmware (MPLAB X project)

Feel free to re-use or modify this project to fit your needs, or use as a reference for PCB design or PIC software development.

Finished product

A range of final images can be found in the media folder.

Bill of materials

MPN	Type	Quantity	Unit cost (GBP)	Purpose
PIC12F683 (DIP)	Microcontroller	1	£0.45	Controls visual animations and user input
74HC595 (DIP)	8-bit Shift Register	1	£0.05	Controls outputs to outer blue LEDs from the MCU
N/A	3mm Blue LED	8	£0.01	Outer LED ring
N/A	5mm Green LED	3	£0.01	Inner LEDs (PWM-driven)
N/A	5mm White LED	1	£0.01	Inner strobing LED
2N3904 (TO-92)	NPN Transistor	10	£0.01	Drives each individual controllable LED group (8x Blue, 1x Green, 1x White)
N/A	SPST Momentary Switch	1	£0.30	User input for changing displayed animation/colour
N/A	1000μF (25V) Electrolytic Capacitor	1	£0.10	Supply voltage smoothing
N/A	100nF (50V) Ceramic Capacitor	1	£0.01	Decoupling capacitor for MCU
N/A	10k Resistor (1/4W)	1	£0.001	Input switch pull-down resistor
N/A	1k Resistor (1/4W)	10	£0.001	Transistor base current limiters
N/A	150R Resistor (1/4W)	8	£0.001	Current limiter for blue LEDs
N/A	120R Resistor (1/4W)	3	£0.001	Current limiter for green LEDs
N/A	62R Resistor (1/4W)	1	£0.001	Current limiter for white LED

Total component cost: £1.15
PCB panel cost (DIY): £0.35
Total cost: £1.50 (Not including etchant, solder or original tree product)

---

Design notes & constraints

There were various constraints throughout this project, the most difficult one being that I could only produce a single-sided PCB, making overlaps impossible without using space for a 0Ω link. The size of the board was also restricted to 68mm x 92mm, otherwise the module wouldn't fit into the tree's current plastic base housing. Drill holes also had to be made and inserted at defined locations so the board could easily be screwed into the unit using pre-existing screw mounts from the previous incandescent arrangement.