GuzZzt.com - Script and Software

Word Clock
Inspired by QLOCKTWO and other word clock projects I wanted to design my own clock. I stared by sketching up some design goals.

I wanted it to have a little more LEDs than QLOCKTWO 11x10 and showing something more than time.
I wanted it to be fit in a 50cm x 50cm IKEA Ribba frame with a 30cm x 30cm picture mount.
I wanted full RGB and full control over all letters/pixels to be able to make some cool effects.
To keep the costs down I order my PCBs from Seeed Studio and I wanted it to fit on 3x3 identical PCBs, each being 10cm x 10cm.
I wanted it to always show the correct time, so some kind of remote clock sync.

At start I looked into showing the clock with 1 min presision but changed my mind to 5 min presision since 1 min is not really used in natural Swedish way of saying the time. Thinking of other stuff to show I setteled on showing date as well. To fit the goal to have 3x3 PCBs the numer of LEDs had to be dividable by 3. Trying to fitt all the words together I ended up with 18x18 LEDs having 6x6 LEDs on each PCB.

Hardware Design
To get the 3x3 PCBs but still sharing the same PCB layout I designed all the control circuits on one side and then using solder jumps to select what position the board have in the 3x3 matrix. The LEDs and decoupling capacitors is on the other side.

For LEDs I choosed WS2812. They are quite nice with a built in control ship and have full 24 bits RGB. This way I didn't need a lot of extra chips for multiplexing etc. Each row is its own databus. Data-out on the first LED is connected to the second data-in etc. With 324 LEDs it would not be possible to have them all connected in a long bus and still have a good frame rate. Since a used the STM32F103RET6 cpu I had plenty on pins and could use 18 for data-out without any big problems.

I used the 72MHz STM32F103RET6 Arm cpu from ST, it works well and is easy to work with. I ended up using far from the 515kb flash memory (more like 30-40kb) but since I use the same cpu in different projects I like to not being limited by flash size. And I might extend the software in the future and some stuff like images/animations etc can easily take a lot of memory.

For time sync I searched around I bit until I finaly found this very nice GPS from PV Electronics with a window sucker. Since it uses normal GPS NMEA messages over serial communicaiton it is easy to connect.

This was my second surface mount project and the first with components on both sides. But soldering it all together with my hot plate worked very well since only one of the nine boards had components on both sides.

To cut out the letters I used my Silhouette Cameo that I originaly bought for PCB solder stensiles. It is two layers, bottom layer in paper to block the light and the top layer is vinyl still on its sheet of protection film. This way all the little details is still there and the light from the LED is more even.

Software Design
Still to come...

Stuff
	Split Flap Display Building a split flap display.
	Word Clock Showing time/date with words.
	Hot Plate For reflow soldering.
	Jenkins Build Status Sign Show the nightly build status.
	Light Painting Stick Paint images with light.
	Vattenkylning Vårat vattenkylnings projekt.(Swe only)
	Links Some useful and cool links.