Simple counter/clock

4-bit counter hooked up to 7-segment display showing succession of hexadecimal digits

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This is intended to be an astable multivibrator-driven 4-bit counter, which is itself drives 7-segment display through diode-matrix ROM.

Counting circuit consists of modified astable multivibrator circuit with three NAND, master-slave data flip flops connected as series toggle flip flops, thus I have 4-bit counter. The dtl gates have LEDs instead of pairs of conventional diodes to slightly save on part count and cost. In addition, this scheme provides visuals for gate working.


Elements of counter and decoder are stacked and wired together.

JPEG Image - 759.65 kB - 04/14/2017 at 04:42


  • 14 × Yellow LEDs
  • 28 × Red LEDs
  • 2 × Green LEDs
  • 3 × Blue LEDs
  • 224 × Diodes 1N4148

View all 8 components

  • Finished!

    Pavel04/22/2017 at 08:00 1 comment

    The thing is now complete and working!

  • Solution is found!

    Pavel04/20/2017 at 03:56 0 comments

    The humble diode AND was not to blame after all, it was prior wiring that was faulty.

    Here are simplified schematics with voltages:

    1) original wiring:

    collector of Q1 was wired directly to base of Q2, to achieve second inversion, thus making buffer; simultaneously from the same collector was the tap to the AND gate of decoder, as inverted input. Failed. the solution was to make this into two full-fledged invertors, and after this modification all started to work as it was intended to.

    2) corrected wiring:

  • Problem with output logic levels

    Pavel04/14/2017 at 04:51 0 comments

    For decoder I used simplest diode 4AND logic gates (image), assuming they would work properly, and give +Vcc for high and 0.6V for low.

    Unfortunately, output for HIGH is measly 1.6-1.7V and it is too low for driving display unit.

    I am still cannot understand, why is it so.

View all 3 project logs

Enjoy this project?



Dr. Cockroach wrote 04/20/2017 at 07:31 point

Very good project :-) Almost the same issues I have had. Keep going :-)

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Pavel wrote 04/20/2017 at 04:29 point

Someday, maybe)   First, I have to learn how to use quartz oscillator though. And full-fledged clock will consume much more parts, time and effort.

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Yann Guidon / YGDES wrote 04/20/2017 at 04:51 point

What a coincidence. I have designed a few quartz oscillators :-)

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Yann Guidon / YGDES wrote 04/20/2017 at 04:23 point

Admit it : you want to build a clock ;-)

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