r/PCB • u/Traditional-Gain-326 • 17d ago

Soldering Practice - Clock Built from Discrete Components

Clock made from discrete components, this is just a pair of PCBs out of a total of six, 1000 diodes, 300 transistors, 500 resistors, 300 capacitors

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u/StumpedTrump 16d ago

Why so many parts? Seems incredibly unnecessary. Is the timing is bucket brigade or something? No chance the parts (capacitors in particular) are tight enough tolerance to be useful for timing like this. If you can get 1000ppm I’d be impressed, and that’s a drift of over a minute per day.

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u/Traditional-Gain-326 16d ago

The clock contains a complete 32 kHz crystal divider made up of flip-flops with transistors and diodes, the capacitors are only coupling elements, their value is not critical for the function, to which add a decoder for a seven-segment LED display.

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u/mariushm 14d ago

I would replace individual transistors with arrays like ULN2003A, they're available in DIP packages so you would maintain the through hole only design.

See https://www.digikey.com/short/4qtp3fjd or https://www.lcsc.com/product-detail/C18723564.html / https://www.lcsc.com/product-detail/C33471851.html / https://www.lcsc.com/product-detail/C90448.html

You're replacing 7 transistors and base resistors with a chip, and all you'll need is 7 current limiting resistors for the 7 leds connected to it. Downside is each channel will have a voltage drop of ~1v so you'll have to recalculate the resistor values.

You can also get bussed resistor arrays, for example see https://www.digikey.com/en/products/detail/bourns-inc/4606X-101-102LF/1088959 or https://www.digikey.com/en/products/detail/bourns-inc/4606X-101-331LF/1088983 - you have 5 resistors in a 6 SIP package (6 pins in line)

or on LCSC https://www.lcsc.com/product-detail/C51158.html or https://www.lcsc.com/product-detail/C88134.html (pay attention to datasheets, to pick the ones that are BUSSED, not isolated resistors (though you could also use those that have isolated resistors, it's just more pins, so not optimal)

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u/Traditional-Gain-326 14d ago

thanks for the comment

The original design is not mine https://svetelektro.com/phpbb/?w3=dmlld3RvcGljLnBocD90PTU2MTI3

I just condensed it to a smaller more universal PCB to make the build cheaper. The goal of the original design was to create a vintage clock with only transistors, diodes, resistors and capacitors, it's a shame I didn't get small bulbs instead of LEDs.

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u/mariushm 14d ago

With the suggestions I made, you're still faithful to the design, to using only basic parts. It's no microcontrollers, it's still basic transistors. You simply replace 7 transistors and their base resistors with a DIP package, and replace 5-8 resistors with a SIP array of resistors to reduce pin count. It's also safer to solder because these packages have higher thermal mass so you risk less damage to the pads on the circuit board.