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I have a task to make frequency divider by 12, 17, 30. I have figured out how to make divider by 12 using staging dividers by 6 and staging dividers by 10. But 17 is odd number and i can't make it like others two. Like on the image using staging flip-flops with divider by 2 and by 6 i can get division by 12.

d flip flop divider

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    \$\begingroup\$ What technology are you using for this exercise? 12 and 30 both have odd factors. Add the information into your question (not in the comments). \$\endgroup\$
    – Transistor
    Commented Oct 2, 2021 at 8:19

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But 17 is odd number and i can't make it like others two

If you want a rough and ready circuit, the old and well-trodden "divide by \$2^n - 1\$" method using an exclusive OR gate should be sufficient. So you can can make a divide-by-three using a divide-by-four circuit and one exclusive or gate. Then cascade this with a divide-by-6 circuit and you have a divide-by-18 circuit. Using the same exclusive or gate trick this can be made into a divide by 17. Schematic of divide-by-three: -

enter image description here

Waveforms: -

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As you can see the Vout waveform (red) is the input clock (blue) divided by three. So, if you want a divide-by-six then use a divide-by-eight and two exor gates: -

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As you can see the above circuit takes a divide by-eight and, using two exclusive or gates, turns it into a divide-by-six.

So, cascade the divide-by-three and the divide-by-six to make a divide-by-eighteen then, using another exclusive or gate make it a divide-by-seventeen: -

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The above is a divide-by-seventeen circuit.

I have a task to make frequency divider by 12, 17, 30

I think you should be able to figure out the divide-by-thirty for yourself but, if you need help, leave a comment.

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  • \$\begingroup\$ Thank you, thats a detailed answer! \$\endgroup\$
    – FgSFDW
    Commented Oct 2, 2021 at 9:29
  • \$\begingroup\$ Hope it helps you. \$\endgroup\$
    – Andy aka
    Commented Oct 2, 2021 at 9:31
  • \$\begingroup\$ @Andyaka could you by any chance recommend a literature explaining "divide by 2^n−1" method? I've successfully used your example to make divide-by-11 circuit but I am not sure I understand the theory behind flip-flop & XOR combination. \$\endgroup\$
    – Ivan Demyachenko
    Commented Oct 30, 2022 at 12:24
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    \$\begingroup\$ @IvanDemyachenko I learnt this technique some time in the early 1980s so unfortunately I have no links to what it was that I read nor can I remember what it was. Theory is simple, the XOR adds an extra clock cycle to the counter and you can see this in the waveforms I provided. Please feel free to upvote if you found it useful. \$\endgroup\$
    – Andy aka
    Commented Oct 30, 2022 at 12:39

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