The idea behind this project was to make a word clock that would be easy to build, so that I could make a few of them.

One of the most time-consuming part of making a Word Clock is building the "light wells" that separate the light for each word, and creating a diffuser that spreads the light evenly but does not dim it excessively.

My idea was that I could use a two-headed 3D printer to print the walls of the light wells, and simultaneously use the second head to print the light diffuser, all in one pass.

It worked great. I was able to find a combination of diffuser material and thickness (and distance from the LEDs) that created evenly-spread illumination. And of course, the vertical walls separate the light for each word and prevent any light from bleeding to adjacent areas.

Step 1: The Light Well Piece

I used a two-headed 3D printer to print the light well piece -- the black walls were printed with black ABS using the Left print head.

The Right head printed a thin (0.05") layer of translucent ABS material to diffuse the light. "Natural" ABS is milky clear, and was perfect for this application.

Note: If you are thinking about purchasing a 3D printer, I strongly suggest a two-head printer. Not only can you print two-color pieces, you can print dissolvable support material with one of the heads. This means you can print items with overhangs and under-cuts, which allows you to print things that are impossible with single-head printers.

Step 2: CAD File and 3D Printing

I created the 3D CAD file (model) using Autodesk 123D Design, which is free, and is easy to use for creating items like this.

Printing a two-color item in a single print pass has just a few more steps than usual. I printed the part using a Makerbot Replicator 2X (two heads) 3D printer.

One thing to know is that you have to create two separate .STL files, one for each color (one file for each print head on the 3D printer). The Autodesk software helps with this -- you select one portion of the model (parts that will print in one of the colors) and create one .STL file, and then select the other portion and create the second .STL file.

To prepare for printing the two-color item, you start by opening one of the .STL files in the Makerware software, and then "add" the second .STL file. Using the Makerbot software, you assign the Left head to one portion (one of the .STL files), and then assign the Right print head to the other portion.

Printing this part at the "standard" resolution takes just over six hours.

Step 3: Schematics

The next thing to do was choose the microprocessor, the clock IC, and how do you drive all of those LEDs anyway?

Microprocessor. I am very familiar Micrchip's PIC family, so I selected the PIC16F688. It costs only $1.40. Wow.

Clock IC. I wanted high accuracy, a serial interface, and battery backup. The DS3231 is perfect.

LEDs. For white light backlighting of each word, I'm using Digikey 1080-1212-1 LEDs. They are small surface-mount LEDs that can handle 30 mA of peak current. There are 72 LEDs in the clock.

LED Drivers. I wanted to be able to dim the LEDs to match the light level in the room. This makes the MAX7219 (or 7221) drivers a natural choice.

Miscellaneous. Rounding out the parts list is a small CdS photocell to detect light levels, a DIP switch for configuring clock options, two push buttons to set the time, a CR2032 battery holder, and 5V regulated wall wart.

I entered the schematics using KiCAD, and then used KiCAD to layout the PC board. I can recommend KiCAD. I found that I needed to create a few schematic symbols and PC footprints, but the price is right (it is open source and free) and has a fairly good feature set. There are no board size limits, and no layer limitations. Sweet.

Word_Clock_Schematics.pdf
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Step 4: PC Board Layout

Because I wanted to make a few of these, I decided to create a two-layer printed circuit board (PCB).

Using KiCad, this is not too difficult. Note that I added a back-side silkscreen as a "Christmas card" that you see if you open the back of the clock.

I have attached the KiCad source files for the schematics and PC board ("schem_pcb_source_files.zip"). If you simply want to have some PCBs fabricated, you could use the "fabrication_files.zip" file, also attached.

PCB ERRATA: The footprint for the button-cell battery (CR2032) has the polarity reversed. This created the need for the cut-and-jumper modification (using red wire-wrap wire) you see in the final assembly pictures.

I sent the fabrication files to pcbnet.com and was happy with the result. There are similar companies that will also provide quick-turn, low-volume PCB fabrication. The cost for 20 boards was just over $10 per board.

Step 5: Software

The software is fairly straight forward: the main( ) loop reads the time from the clock chip, then reads the room ambient light level from the sensor, and then turns on the appropriate LEDs to light up the proper words, at the correct brightness. (The LEDs are dimmed if the room gets dimmer, for example.)

Because the controller is a PIC chip, it made sense to use Microchip's MPLAB X Integrated Development Environment (IDE). Microchip has a free C compiler available, called the MPLAB XC compiler. It is functional and easy to use.

The software source files are attached.

CUSTOM FEATURE: Our family has a saying "Family is forever." I created the front panel word mask to include the words "family" and "ever" so that at precisely 4 o'clock each day the clock reads "FAMILY IS FOUR EVER".

Word_Clock_code.zip
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Step 6: The Word Mask + Display Box

At the front of the clock is a word mask. It sits on top of the light well piece to create the word display.

To mask out each word, I tried a variety of materials. The best material was thin (1/16") opaque black acrylic, from Inventables.com. It cuts easily with a laser cutter, and does not bleed light between words.

One disadvantage of using a sheet of acrylic for the mask is that there can be no "loose pieces" in the letters. For example, the middle of the letter "O" has to be connected. This required some modification to the font, as can be seen in the attached image and .PDF file.

The enclosure is a commercial 6" x 6" x 1.5" shadow box that can be purchased at Michael's.

Step 7: Final Assembly

After the PC board has had the components soldered on, the 3D-printed "light well" piece is attached to the PCB using screws.

The "word mask" is glued to the top of the "light well" piece, after careful alignment.

The rear-panel of the clock has a power jack, and two pushbuttons for setting the time. This is just a matter of drilling three holes, and connecting them to the main board with short pieces of two-conductor wire.

These pieces then slide into the case.

The power source is a 5 volt regulated wall wart. Once power is applied, the clock time is adjusted easily using the two switches (hour and minutes) on the back of the clock.