Digital password lock circuit composed of CD4520

As shown in the figure, the universal digital password lock circuit is composed of CMOS digital integrated circuits, which are characterized by wide power supply voltage range, low power consumption, good anti-interference performance, and few peripheral components. The password lock has a total of 256 password combinations and is equipped with a pseudo code switch, which has good security characteristics. Its circuit composition is shown in the figure. The password lock circuit is composed of a dual binary synchronous add counter CD4520, which contains two binary counters with the same structure. Each counter has 4 output terminals: Ql~Q4, a pulse rising edge trigger terminal CP; a falling edge trigger terminal EN non, and a reset terminal R. The two counters share a positive power supply terminal and a negative power supply terminal.