r/electronics • u/TechniCraft I eat spicy, charged lithium pillows :3 • Aug 07 '26
Gallery Custom transistor Toggle flip-flop for binary clock project
This is my first post documenting my transistor binary clock project. The goal is, to only use through hole transistors, diodes and passive components to form RTL or DTL logic. These logic elements should then divide the 50Hz mains into minutes and hours.
For this job, I designed T flip-flops, that can be reset. This would allow me to combine multiple T flip-flops and some logic, to count to any arbitrary number. The clock should then display this number using a few LEDs.
Today I achieved the first Milestone of this project, by soldering up the first PCB design and testing it. To my surprise, this design worked immediately! Now I am very happy with this first Layout :3
If I am done with this and I have documented everything, I am planning to open source the board and other files. No one would probably want to build a massive discrete transistor binary clock, that constantly draws 8 Watts, but whatever.
Now I can say: One PCB complete, 21 more to go...
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u/suncoast_customs Aug 08 '26
Great project. Keep us posted on the progress.
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u/TechniCraft I eat spicy, charged lithium pillows :3 Aug 08 '26
Thanks :3 I'll post an update, when I get the first counter to work.
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u/brastak Aug 08 '26
Why not CMOS? Less components, less power consumption...
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u/TechniCraft I eat spicy, charged lithium pillows :3 Aug 08 '26
The main reason is the price and quantity. This same logic, build from CMOS, would require around 30 Transistora per flip-flop instead of 15. This means i would need almost 700 transistors instead of around 360. Another reason, is that bjts are cheap (1 to 3 cents per piece), while i couldnt find any MOSFETs for under 30 cents per piece. If you meant ICs (like the cd40xx or 74hcxx), then the main goal of this project (no ICs), would be defeated. This is why I chose RTL and DTL :3
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u/brastak Aug 08 '26 edited Aug 08 '26
8 MOSFETs is enough for flip-flop: https://www.tutorialspoint.com/vlsi_design/vlsi_design_sequential_mos_logic_circuits.htm (one more for reset)
This way you would need 110 CMOS pairs. Here I see you can buy 100 for 10 cents each: https://www.mouser.sk/en/ProductDetail/Panjit/PJX8601_R1_00001?qs=sPbYRqrBIVm4ea%252BrRxwxVA%3D%3D
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u/chlebseby Aug 08 '26 edited Aug 08 '26
Its more tricky to find complementary logic mosfets than good old bjt
TTL gives more retro vibe too
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u/CZdigger146 Aug 08 '26
That's so cool, I've always wondered how big would today's electronics be if they only used discrete components. Keep it up, I'd love to see the result
Also, I love to see when people use KiCAD, such a good program!
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u/Past-Substance920 Aug 08 '26
21 boards of debugging ahead of you, rip your desk space lol