Pure TTL Based Clock

We’ll just say, [Kenneth] really likes clocks. His most recent is a pure 7400 series TTL based one, ie no microcontroller as seen in the past, here, here, and here. The signal starts out as a typical 32,768 crystal divided down to the necessary 1Hz, which is then divided again appropriately to provide hours and minutes.

As far as TTL clocks go, this is nothing too original; until it comes to his creative button interface. By using a not as sexy as it sounds multivibrator, he can produce a clean square wave instead of the figity signals produced from buttons to advance and set the time. Like always, he also provides us with a thorough breakdown of his clock, after the jump.

[youtube http://www.youtube.com/watch?v=rzDe7GBJ0V8%5D

28 thoughts on “Pure TTL Based Clock

  1. I had to build one of these for my electronics class in high school. This is a sheer test of will when it comes to the wiring and debugging :-S pull your hair out looking for the one wire or gate that’s not behaving! TTL probes are your friend!

  2. First he says “Look at my purely TTL based clock”, then his first sentance regarding the hardware is “using a CMOS NOR gate”.

    10 points for anyone who spots the error :)

  3. @smoker_dave: I thought that was a bit odd myself!

    I too built one of these at school (there were some bizarre “no programming allowed” rules in electronics and IT), but used 555s to debounce the switches as Kenneth mentioned he previously did.

    Is the “z” in “hertz” silent in the USA?

  4. While I (as a geek) recognize just how basic any pure logic gate construction is, to a novice it still just looks like a bunch of those-black-thin-electric-things that everything’s build out of.

    A transistor-diode-logic clock[SIZE=1](1)[/SIZE] is a much better presentation of how much stuff actually goes into something as simple as a clock.

    For future reference, I still think this is wicked awesome.

    [SIZE=1](1)http://hackaday.com/2010/01/11/194-transistor-clock-will-blow-your-mind]transistor-diode-logic clock[/SIZE]

  5. @Ben Ryves
    “Is the “z” in “hertz” silent in the USA?”

    Shouldn’t be. He does say it right when talking about the crystal frequency, don’t know why he changes it later

  6. @razor

    I did exactly the same for my A level electronics projecrt, managed to knock a breadboard out of place on the hand in date and it stopped working. Still, seems a bit odd that this is front page worthy – after all it’s exactly what you’d expect to see in a high school project.

  7. Old-skool! Circa-1980 design right there.

    What’s with the construction faux-pas though? Red wires for ground? Yellow wires for ground? Red wires as signal wires too? Where are the decoupling caps on the ICs?

    If you’re going to go to all that hassle and expense to build something like this, a few extra pennies for wire and passives to do it right are well worth it.

    Kudos for the success

  8. Haha. Wow guys, I had never noticed that before. Guess I’ll have to add my silent z problem to my list of linguistic quirks to work on.

    I kinda hoped you all would let me slide on the one CMOS gate for the crystal. Guess not…

    @ian: You caught me. I started placing bypass caps by the oscillator, but took a break and forgot to finish the job, and the clock has been working without them. I have a bag of 500 of them, so there’s no excuse other than being tired and lazy. As for the wire colors, it’s just a matter of the fact that I inherited a 1000′ spool of red/white bell wire, so I’ve just made do with two colors + a set of breadboard jumpers. I’m usually more organized in board layout (red for data, white for clock, etc), but this project just spiraled out of control. Wire routing is a very subtle art.

  9. I would like to see 2 conveniences added for the lurkers and shirkers and part-time workers: a glossary accessible with a right click, and for those with Hack a Day on their iGoogle homepage, LONGER (timewise) blurbs when the cursor hovers over the link. The captions are usually three times longer than a fast reader can scan before they disappear. This is google’s purview, but I am writing here because this crowd is the smartest crew since Redstone arsenal hired Von Braun(and my Dad).

  10. I’ve always wanted to do this, but as a binary clock instead.
    Not those half assed binary clocks with four rows of leds, one for each digit, I wanted to do a 24 hour binary clock, one 5 bit row of LEDs for hours, one 6 bit row for minutes.
    You can only build so many ISA cards and EPROM programmers before you want to do something else.

  11. Partially correct h4rm0n1c, the point is that CMOS and TTL are completely different logic families all together (their internals are made in completely different ways).

    Only 5 points to you.

  12. Reminds me of a project I once made. Battleship using only logic and no programming! We used Oscilloscopes as displays and made our own “graphics card”, input and game logic. Only initial setup was done via a PC interface. (This was also possible via the logic, but this was rather tedious)

  13. Um yeah built one of these with my TTL cookbook 12 years ago. How is it a hack? This is the problem with jumping to Arduino without first learning basic electronics. Should be categorized under “How to”. Kudos to the builder, bless his heart. Not trying to demean his work, just come on HAD…

  14. @BlackCow: I used 74160 decade counters, so I don’t see how 7490s would have made it any easier.

    @dana: Because if I made PCBs for every project I built, I’d be swimming in projects. With the breadboard, I can build the project, document it, play with it for a few weeks, then take everything out and sort them back into my parts box.
    The capacitors in the schematic are for the 74123 oscillators. The other capacitors are to filter the 5V coming from my power supply to prevent glitching in the logic gates from an unstable power supply.

  15. It’s funny how people think it’s cool and retro as hell to build with 7400 series devices, when you’ve worked with this for “real” when it was state of the art.
    At the time, I could remember the pinout of all devices in the 74xx series ;-)

  16. Hi there, I am building a 7 segment digital clock which entirely work on 7490 and 7447 TTL IC. I want to use crystal oscillator to produce 1 hz clock signal. Can you send me the schematic circuit diagram for your project to help building my project thank you.

  17. I am working on home automation project. I am not able to get 48Mhz crystal and so i have to use TTL to generate this frequency. But i have no idea how to do this. So can you help me with this problem.
    Thanks in advance.

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