Digital clock building


[punkky] has been documenting his adventures building digital clocks. They each use six 7-segment LED displays, but he’s been gradually changing how they are built. The first version used a CMOS BCD-to-7-sement latch on each display, which is tied to a PIC16F627a. For the next run, he added multiplexing, so he could drive all the segments using just thirteen pins. He’s posted a final schematic with code and details of how the clock timing actually works.


  1. error404 says:

    Pfft :P The PIC is cheating! We had to do it with 74xx logic and a 12VAC transformer alone!

  2. khani3s says:

    I am projecting a one with only 74xx logic, 555 and discrete components… With ALARM!

  3. thethirdmoose says:

    Yea seriously… Why do you need a uC for this?

  4. ryan says:

    if he really wanted to be cool, he’d use nixie tubes. :P

  5. bigdue says:

    Not sure on the required gate count, but what about using a CPLD like in one of the previous entries here?

    khani3s, how do you plan to implement an alarm? Some type of FSM?

  6. mike says:

    You could do the alarm with some ‘ls85 comparators, a RS flop, and a 555 (or buzzer) for the sound.

  7. Wes says:

    If it doesnt need to be battery powered, you could step line voltage down to 5v, clean the wave up with a schmitt trigger, and set up a frequency divider to get a 1pps square wave. The 555 would be easier nvm XD

  8. punkky says:

    Thank you for all comments. As I stated in my blog, I built this clock for learning Microcontroller. I’m not looking for an easy way to build a digital clock :)
    Alarm might be the next feature to be added.

  9. sonyawontrun says:

    yeah an alarm would be a good idea.

  10. Gene D. says:

    We all have to begin somewhere. It is a good learning project. I have made a clock using 74′ series IC, programable counter, keyboard entry, latches for alarm and a comparitor circuit.
    I have many PIC’s, basic stamps, Z80 and ….. But I still injoy the extream challange of designing a circuit without any programming…stuff.
    Good job!!!

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