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I am not a professional in this area, so I hope I am asking questions correctly.

I have a 5 V clock pulse with 50-200 Hz (square wave) and would like to build a simple unpowered clock divider. Output should be 1/2 of input frequency. So it's literally skips every second beep.

There are a lot of solutions with decade/ripple counters I've found, but all require at least 2-3V of power supply. I've read a lot of JK/D flip flops but got frustrated with too many information and zero experience in this area.

I assume I need a module that should have some kind of solid state 1 bit memory that will be not power dependent. If it's even possible and exists.

TLDR: Need a passive module that I can put in the middle of the clock signal wire, that halves the frequency.

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    \$\begingroup\$ Note that 1/4 of the time, the output will be powered even though the input is not powered. Where should the power come from? \$\endgroup\$
    – user253751
    Jan 31, 2020 at 15:44

2 Answers 2

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Use a diode to charge up a cap to 5v -0.6v = 4.4v

Now run a D FF on that 4.4v, with Qx tied to D so you get the div_by_2 behavior.

To protect the FF, or just avoid bad behavior, use a 10K ohm resistor (brown, black, orange) in series with Clock input of FF. This is because the +5v clock signal will slightly turn on the on-chip ESD diodes and inject current into the FF substrate, with unknown affect of FF behavior. Inserting a moderate-size resistor will prevent this.

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    \$\begingroup\$ Yup. It can't be unpoweerd, but it can be self-powered. Consider a Schottky diode to minimise voltage loss, and use a CMOS 74HC) F/F to minimise power. \$\endgroup\$
    – user16324
    Jan 31, 2020 at 15:53
  • \$\begingroup\$ THANKS! This is super useful! But there is a huge range of D FF's there (even in 74HC family) and get lost in all those spec sheets... Any particular kind that will work for me? And 1 last question – if I would like to make /4 or /8 division should I use a sequence of single D FFs or use a module with multiple Q's? If I got it right \$\endgroup\$ Jan 31, 2020 at 16:56
  • \$\begingroup\$ If in doubt, 7474 (74HC74). (But many others will do too) \$\endgroup\$
    – user16324
    Jan 31, 2020 at 17:23
  • \$\begingroup\$ @DenisZarubin sort by price, does the cheapest one do what you want? then use that one. otherwise maybe check the next few or fall back on whatever comes up when you google "d flip-flop chip" \$\endgroup\$
    – user253751
    Oct 28, 2021 at 12:35
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Assuming your square wave signal has a 50% duty cycle, then it will have an average voltage of 2.5V. If the source of the square wave is able to supply enough power, then it may be possible to add some circuitry ( a simple series resistor followed by a capacitor ) that will be able to convert the square wave into something more stable, that can be used for a low-power D-type.

There are a lot of ifs and maybes here - if you let us know a little more about the setup you have, in particular what is generating the square wave, then it will be possible to say if this approach will work.

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  • \$\begingroup\$ It is a square wave 0 to 5 volts that goes from clock unit of a modular synthesizer. It triggers envelopes which modulate sound oscillators and stuff. There are some existing modules which can divide clock on all kind of ways, but all require power. I was wondering if I can create a cable "cut-in" module which can divide clock 2, 4 or 8 times. \$\endgroup\$ Jan 31, 2020 at 16:23

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