In April I set about beginning to build a Word Clock using Doug Jackson’s Instructables article. It’s taken me a long time, but I’ve made some progress! I thought I’d make a post documenting how I made it to help anyone thinking about building one.
CAD Model: I started by putting together a CAD model of the clock using Solidworks – as the design of the partitioned lightbox was quite complicated this was a really useful place to start.
I used the CAD model to make sure the LED strips would fit properly behind the letters. You can cut the LED strips into lengths of multiples of three LEDs – in this case, I either used three or six LED strips.
Laser Cutting Lightbox: The lightbox and partitions were cut using a laser. This let me accurately reproduce my CAD model in black and clear acrylic with minimal waste material.
Partitioned Lightbox Assembly: I did a dry assembly of the partitioned lightbox, unfortunately I didn’t quite get the fit right for the finger joints used on this assembly. To fix this, I painstakingly wrapped tiny pieces of tape around each of the ‘fingers’ to achieve a tight interference fit.
Affixing LED’s: The self adhesive LED strips were stuck down to the backing of the lightbox. For convenience, I engraved the lightbox backing with the LED positions during cutting as well as including all the holes required for wiring.
PCB Etching: The PCBs were developed using the stencil provided on Instructables and etched using chemicals from Maplin.
Completed Controller: The board was assembled using an ATMega 168 20-PU which I bought with the Arduino bootloader already burnt onto it.
You should be able to program the controller using a USB FDTI cable, however I couldn’t get this to work. I ended up transferring the microcontroller to an Arduino Uno board to program, however I could still monitor the serial output of the board via FDTI.
Wiring the LEDs: The LED’s had a common + wire connected to them and a switched ground. Strangely, the solder tabs on the LED strips were marked + and -, however these were the wrong way round! That might explain why they were so cheap (ordered from Ebay, delivered from Hong Kong)! This highlighted to me why it’s important to test things and then test them again.
The Stencil: The stenciled front cover was made using a vinyl decal, the individual letters were weeded to allow the words to be illuminated. Some diffuser material was stuck down in between the partitioned lightbox and the back of the stencil front cover in an attempt to make the letters ‘glow’.
The Finished Product:
The full set of photos for this article are on Flickr.
