Principle circuit diagram of password electronic switch

Working principle: The circuit working principle of this device is as shown in the figure. The password electronic switch is designed with three unlocking buttons, and has a time limit circuit, error code lock and electronic alarm circuit. Only by pressing the unlock buttons AN1, AN2, and AN3 correctly can the relay J1 be excited and closed, and its closing time is determined by the values ​​​​of R1 and C1. It can be seen from the figure that the transistors VT5, VT6, and VT7 are connected in series to form an AND gate logic circuit. If any one of these three transistors is cut off, the relay J1 will be released. The five buttons AN1-AN8 are connected in parallel to form an OR gate logic circuit. Pressing any one of the buttons will cause the conduction of the transistor VT4, so the ① and ② pins of LSE are connected in collusion, and its ④ pin outputs a high level. Relay J2 is excited and closed. After J2 is closed, the normally closed contact j2-1 is disconnected, cutting off the power supply of the unlocking circuit. At this time, no matter how you fiddle with AN1, AN2, and AN3, it is invalid. The blocking time is determined by the values ​​​​of R4 and C4. At the same time, the normally open contact j2-2 of J2 is closed, turning on the power of the alarm and emitting an alarm sound.

The application circuits of LSE are far more than these. It has great "use" in anti-theft control, daily life electrical appliance control, and industrial and agricultural production automation control.