Transistor Logic Clock Has 777 Transistors

Sometimes, the parts list says it all. 777 transistors, 1223 resistors, 136 LEDs, 455 crimp connectors, 41 protoboards and 500 grams of solder. That’s what went into this transistor logic clock build.

While additional diodes and capacitors were tolerated in this project, a consequent implementation of a discrete transistor logic clock, of course, does not contain a quarz oscillator. Instead, it extracts its clock signal from the mains frequency in its power supply. Because mains frequency is slow, it can be stepped down to a clock-applicable 1 Hz by a simple counter unit which already spreads its discrete transistors across 4 protoboards.

In total, 28 Flip Flops were assembled on individual boards. Most of them went into the counters for hours, minutes and seconds. The counters are orchestrated by reset boards that know how far each counter shall count and resets them when necessary while incrementing the next counter — a transistor-based overflow interrupt. The output of the counters feeds into the 7 segment decoder (2 boards). Eventually, a display multiplexer (3 boards), clocked by a 300 Hz timing circuit based on a 555 timer, also implemented from discrete components, sends the numbers to the display.

Fine tuning the clock speed may require a quick call to the electricity provider, but the end result is nevertheless a beautifully crafted, modular transistor logic clock!

This is good news for those of you who have been coveting the MOnSter6502 project. Practice your SMD transistor PCB layout with this project before you try to recreate that monster of a board layout project.

Thanks to [BB] for the tip!

Filed under: clock hacks

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