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Simple pulse generator with accurate frequency 1Hz

This circuit is ideal for clocks and anything that has to do with time measurement. The output pulse comes every one second with great accuracy (without being affected by environmental interferences or time). Its accuracy is based on a quartz crystal oscillator, which guaranties that your clock will not desynchronize.


The piezoelectric crystal is the most critical component and may hard to find. You must use only the one I suggest. In any other case, the output won't have the exact frequency of 1Hz. If you want different frequencies we can get the pulse signal from the other output of 4521 CMOS chip.

  • One CMOS 4521 Chip.
  • A 1MŮ resistor (1/4 Watt).
  • One 3.9KŮ resistor (1/4 Watt).
  • One 22pF capacitor.
  • One 82pF capacitor.
  • One piezoelectric crystal 4,194,304Hz. Crystal's frequency is critical. If you use a different crystal, you will not have the exactly 1Hz output frequency.
  • A 16 pin DIP socket (for the 4521 CMOS chip).
  • A small piece of a Veroboard
  • Wire for connections
  • Solder and soldering iron

Also you will need a stabilized 5 Volt external power supply. You can use a 4.5 Volt battery or even a 9 Volt battery. Be aware that with the 9Volt battery the output level will be also at 9 Volt (not TTL logic).

Schematic Diagram

Here is the schematic diagram of the simple 1Hz accurate pulse generator (click on the picture to enlarge).

Attention: The piezoelectric crystal is the most critical component and may hard to find. The circuit can be powered by a various range of different voltages, from 5 to 15 Volts. Keep in mind that the output level depends on the power supply.

Created: 06/07/2007
Updated: -

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