Variable duty cycle square wave generator

The simplest generator circuit can be assembled using logic elements with duty cycle adjustment; it can be built on the basis of Simple square wave generator using logic gates. The main advantage of this generator is nothing superfluous: a timing RC circuit for each part of the pulse and two microcircuit elements.

Pic. 1. Simple variable duty cycle square wave generator using logic gates

Here, the charge and discharge of the capacitor is carried out through different circuits (parts) of R2 thanks to the diodes D1 and D2, so the ratio of pulse and pause will be different depending on the position of the central terminal of R2.

This device can be assembled on any Quadruple 2-Input NAND Gates type chip (For example, HD74LS00P or SN74HC00N or etc). Quadruple 2-Input NAND Gates contains 4 2-Input NAND Gates logic elements. The 2-Input NAND Gates has two inputs, and first applies an AND operation to the two input signals, and then the result is inverted (NOT operation).

The principle of operation is described in more detail in Simple square wave generator using logic gates.

The frequency of such a generator is unstable. The generator output frequency, in addition to the values of resistor R1 and capacitor C1, depends on the supply voltage and temperature. To increase stability, it is recommended to add one or two more 2-Input NAND Gates at the output.