Back in the fall of 2011, I decided to get a little more interested in my major. I had spent the summer fiddling with home-etched PCBs and wanted to take it to the next level. For my birthday the previous June, Katie had gotten me three 6.5″ seven-segment displays from SparkFun. I had some early ideas, but the one that stuck was a hexadecimal wall clock (who needs a tens hour digit anyway?). In hindsight, a pentadecimal clock would have been more logical, as the 15’s minute digit would indicate which quadrant of a traditional clock the 1’s digit was associated with, and the user would have a much easier time converting the nonsense to something useful.
The clock is remarkably simple. A PIC24FJ64GA002 communicates via an I2C bus with a NXP PCA9626 24-bit LED driver. The driver is capable of sinking up to 100mA per pin, an incredible amount for a QFP48 package. The PCA9626 can also PWM individual outputs or the whole set – I decided a 1Hz pulsating feature would be easy on the eyes. The board is run off a 12volt wall adapter and is mounted along with the display in a small MDF/smoked acrylic case. The black acrylic hides most of the abysmal wiring and provides a nice contrast to the brightly glowing red LEDs.
A schematic is lost on some HDD long gone, but the source remains, and you can view it here: main.c