Digital long delay circuit

General long delay circuits usually rely on electrolytic capacitors or high impedance circuits. This type of delay circuit has poor stability and low delay accuracy. What is given here is a digital long delay circuit that completely abandons large electrolytic capacitors and high impedance circuits, and has high delay accuracy. The core of the circuit is the integrated block MC14521B, which is a 24-level frequency division circuit that contains an inverter that can form an oscillation circuit. If the trigger input terminal is grounded or no signal is added, the circuit enters the delay state, and the delay time is adjusted by the range switch X and the 100KΩ potentiometer. If X is connected to point A, the delay is 1 minute 40 seconds to 18 minutes 30 seconds, and if X is connected to point B, the delay is 13 minutes 20 seconds to 2 hours 28 minutes. When X is connected to point C, the delay is 1 hour 47 minutes to 20 hours. The specific delay time is set by the 100KΩ potentiometer. If a longer delay is required, a larger capacitor can be used instead of the 39nF capacitor. At this time, the delay can reach more than a week. Adding a positive signal to the trigger output will reset the frequency divider in 4521B. The delay is reliable and stable, and it is recommended to be powered by a 6-15V regulated power supply. The prototype is powered by a 12V power supply.