Key-controlled volume controller circuit composed of CD4520

The main control element of the volume controller in this example is the optocoupler, which controls the volume by controlling the brightness of the light-emitting diode in the optocoupler, thereby changing the resistance value of the photoresistor in the optocoupler. The brightness of the light-emitting diode is achieved by the number of pulses in the input counter. The circuit composition is shown in the figure.