Kello version 2

The second version of wall clock is very similar to first version. This version was designed in 2003, and was awarded with second prize at our student union HAM club electronics design competition. The main differences are dual color displays and an etched PCB. The clock is still derived from a 4 MHz crystal oscillator with no backup battery, and all logic is implemented in MAX7160 CPLD. The design shortcuts done on first version are also taken properly into account, so displays have current limit resistors and there is location to solder bypass capacitors under the CPLD, even though not shown in schematics. The displays are Kingbright SBA18-11EGWA for hours and minutes and SBA15-11EGWA for seconds. The schematic diagram is available in .pdf below:


Below is an Eagle3d rendered GIF animation of the clock version 2 showing the different colors. Originally the code used PWM to fade between red and green, but I soon got annoyed as the intermediate color between pure red and pure green is rather ugly. The final code changes color at midnight. There was also brainstorming that the colors could be used to indicate working hours at work or lecture hours at school.Seven segment LED wall clock
        version 2

Unfortunately I couldn't find the source code anymore but I'll post it here if it pops out somewhere. However it is very similar to code of the first version. Difference is support to drive the two common anodes to change color, and inverted outputs as displays are now common anode and not common cathode. I and my friends made a total of about five of these version 2 clocks.

The schematic and PCB of version 2 clock are available below. The PCB is single-side with three jumpers. I think I also made some updated design which is single-side without any jumpers, but can't remember if I actually built it or not. The design rules are pretty relaxed, and the board is possible to etch at home with basic PCB etching equipment. That's what I did back then. Eagle .sch and .pcb

Also this second version of the clock is designed to fit in Velleman B8009 housing. These housings are still available for order in some web shops, even though the Velleman K8009 kit and the B8009 housing are discontinued.

page created 1.8.2014
last updated 1.8.2014