Way back in the 80’s – 1986 to be precise since I dated one of the PCBs – I made a ‘Record Time’ clock and it has lived in my parents kitchen ever since. Amazingly it’s still working 33 years later.
It is based on an Intel 8748 microcontroller and looking back now was quite an achievement. I had no development tools for it, just a book, the ‘Osborne 4 & 8 Bit Microprocessor Handbook’ which had a chapter on the 8748 including electrical spec’s and detailed instruction set information. From the information in that book I built a hardware programmer, wrote a two-pass assembler in BASIC along with a rudimentary linker and tool to create an Intel HEX formatted output file. At the time I had never used an assembler and just wrote tools to solve problems. I didn’t even no what a linker was when I wrote it, it was only years later when I got to use real development tools that I found out it was a thing!
The PCBs were designed by hand on to drafting film at 1:1 scale. You could buy PCB transfers with DIP pads and other pad styles on them, the interconnecting lines I drew by hand using Rotring drawing pens of various widths. It was really tedious and took a lot of planning with tracing paper and pencil overlays. There was no rip-up and redraw the traces, or move an IC to make more room.
I had a lot of trouble finding decent bi-colour LEDs that were both bright enough and diffused. In the end I found CQX95 LEDs worked but the company that had them would only sell me 100 LEDs.
I’ve always wondered how long it will keep going – is the EEPROM going to fade away one day? I’ve often thought about doing a modern version but could never get motivated to do it. With access to loads of documentation, good development tools, easy to obtain components, CAD and cheap PCB manufacturing – there was no excuse really. Anyway, having done the ‘Tacho Clock’ over the last few months that had some code I could reuse, I spent a Bank Holiday weekend messing about with some ideas for ‘Record Clock Redux‘.
As you can see above it’s still a work in progress, the code is pretty much done but I want to get a PCB designed and also sort out the construction of the clock.