A Mixed-Signal LED Clock

The term `mixed-signal` is usually reserved for circuits and ICs that process both analog and digital signals. In that sense the title `A mixed-signal LED clock` is perhaps misleading since this is a digital clock from beginning to end. However, the readout is analog and since the beast had to be given a name, I a called it my `mixed-signal` clock
A Mixed-Signal LED Clock - schematic

. Somewhere in the middle of the eighties, when I was studying, I joined the ECA: the Eindhoven Computer Association, a microcomputer club in Eindhoven. Although I am not a member anymore, they still exist and have now been active for more than 25 years [1]. Being situated in Eindhoven, the club obviously had close links with Philips, and regularly obtained surplus supplies of components of various kinds. I remember that these components could be bought for fl 0. 10 (10 guider cents) a piece on every Tuesday evening. At one time they had a batch of LEDs in various shapes and colors. In those days a LED was not quite the common component it is today. The availability of these LEDs in these beautiful colors and nice shapes suggested the idea for a clock with an analog clock face. Normally, I never bother about making a printed circuit board for my circuits. I prefer working on these cheap prefabricated pertinax breadboard cards. However, for the circular face of my LED clock I had no other alternative than to etch a PCB (Fig. 1). I made it in the summer of 1987, and after I had placed the LEDs and finished the wiring, I put it into a drawer. There it was forgotten due to more pressing projects (girls and examinations). Two years ago I found it again and decided to finish the clock. It actually became my first PIC processor project. The circuit of the clock contains no real surprises. A (literally) striking feature about this...

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