My project: Mega Transistor Clock - Page 1
Forum section: electronics / projects

author: Mek
author_rank: Newbie
timestamp: August 08, 2025, 05:19:25 pm
content: Hi every1,maybe you already know this project, but I didn't present it in this forum yet, so here goes...This clock took along timeto complete. It does not contain any integrated circuits and is designed by myself. All parts are common and easily obtainable. Also older parts pulled from old devices can find their place here if they are OK - great way of repurposing old electronic parts.For me, it is a nice accessory of the room and draws attention of my visitors. And completing this project was also an educational journey.Pics are at the bottom of this post. I couldn't figure out how to add them inline, at least they didn't work in preview mode.ParametersDigital and binary time representation24-hour time format, blinking double dots (colons)2 push buttons for time setup (hours and minutes)Crystal resonator as time basePower supply: 5 V / 500 mA max.596 diodes and 221 transistors + a "handful" of other partsPCB dimensions: 48.5 x 37 cm - height x widthThe sections (see block circuit) are named the same as on the PCB - they are also highlighted on the PCB for easier orientation.The oscillator is driven by a watch crystal of frequency 32.768 kHz, its output is similar to sine wave, but with some offset and unsuitable peak-to-peak levels. For further processing, it must be converted into logic levels (square wave 0 - 5 V) and that is the job of the Buffer and Shaper sections.Following flip-flops divide the 32.768 kHz by two as many times as needed in order to obtain a 1 Hz signal that is used to count seconds.Divider by 10 counts seconds, divider by 6 counts tens of seconds. Flip-flop outputs are connected to LEDs for binary time representation, and also to decoders. The decoders determine which segments of the display will light up in which state of the flip-flops.Same goes for the sections to count minutes, but with a little difference - the push button for setup of minutes. When the button is pressed, minutes are clocked by a 2 Hz signal, otherwise they are clocked from the output of tens of seconds divider.The sections to count hours and tens of hours are interconnected in such a way that they count from 0 to 23. Again, there is a push button to set up the hours, that works the same way as for minutes.Reset circuit is also present so that the clock starts from 00:00:00 and not some random state.Dividers by 6, 10, and 24, are sequential logic circuits formed from flip-flops and logic gates made only from transistors and diodes.List of partsNPN transistors (208 pcs)PNP transistors (13 pcs)diodes 1N4148 (596 pcs)electrolytic capacitors 10 μF / 16 V (10 pcs)electrolytic capacitors 1000 μF / 16 V (2 pcs)ceramic capacitors 100 pF (105 pcs)ceramic capacitors 22 pF (2 pcs)ceramic capacitors 100 nF (12 pcs)ceramic capacitors 22 nF (2 pcs)ceramic capacitor 1 nFresistors 150 Ω (66 pcs) - only for V3 - V1 comes with resistors already soldered (SMD)resistors 1 kΩ (74 pcs)resistors 100 kΩ (144 pcs)resistors 10 kΩ (165 pcs)resistors 1 MΩ (2 pcs)resistor 10 MΩresistor 470 kΩcrystal resonator 32.768 kHzdisplay 38.1 mm (1.5 in) red (6 pcs)LED diodes 5 mm red 20 mcd (24 pcs)radial choke 120 μH or similarpush buttons 6 mm for PCB (2 pcs)pin header 1x20, pin spacing 2,54 mm2-lead PCB screw terminal blockThere are more pictures than I was able to attach to this post around the logic gates and other stuff - forum capabilities are limited for such a big project. Please refer tomy web pagefor more information. There is also the whole schematic, assembly manual, and technical documents available for download.I hope you like it

author: Grandchuck
author_rank: Super Contributor
timestamp: August 08, 2025, 07:39:44 pm
content: Very Nice!

author: TimFox
author_rank: Super Contributor
timestamp: August 08, 2025, 09:01:17 pm
content: Nice work!The only thing that would make it better is using only TO-18 metal-can transistors.

author: Benta
author_rank: Super Contributor
timestamp: August 08, 2025, 09:19:02 pm
content: Senseless, but very, very cool!

author: Stray Electron
author_rank: Super Contributor
timestamp: August 08, 2025, 10:37:14 pm
content: Wow, that's an impressive list of parts! It's a good example of why computers or even things like digital clocks, didn't become practical until the wide spread availability of ICs.Thanks for sharing.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 09, 2025, 12:19:25 am
content: Quote from: TimFox on August 08, 2025, 09:01:17 pm.. and BAW62 diodes come in a nice pale blue with red stripe package.

author: Mek
author_rank: Newbie
timestamp: August 09, 2025, 11:07:09 am
content: Thank you all for your kind words.Yes, it certainly is possible to use a wide range of diodes and transistors, also the TO-18 packaged ones. After all, this is just low-frequency low-power switching. But they are a bit bigger so sometimes you need to make some spaceThe picture below is from a clock that I completed by using only recycled parts - mainly transistors with no other use because they had no marking at all. I learned the hard way that the transistors in the flip-flops should be the same, otherwise it will refuse to flip or flop

author: David Hess
author_rank: Super Contributor
timestamp: August 09, 2025, 12:05:43 pm
content: I have thought about doing the same thing but with a discrete implementation of integrated injection logic.

author: jmelson
author_rank: Super Contributor
timestamp: August 09, 2025, 05:26:22 pm
content: Just wondering how you did the flip-flops? Diode steered, capacitor triggered FF is one of the simplest schemes with minimal part count, used a lot in the old days of discrete transistor computers. I wonder how you did it?Thanks,Jon

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2025, 05:31:50 pm
content: Quote from: jmelson on August 09, 2025, 05:26:22 pmFrom the original poster's website.https://mekweb.eu/?q=download-details&f=94&lang=en