This is a circuit Digital combination Lock is simple but effective ease of automatic reset. The circuit is about double flip-flop IC 4013. Two CD ICs are used here. Push button switches are used to enter the code number. One side of all push-button switches connected to +12 V DC. The other end of 2,3,6,8 buttons are connected to the clock input pins of filp-flops. The other end of other buttons switches are shorted and connected to the pin assembly filp-flops.
The relay coil is activated only if the code is entered in the correct order and if there is some variation, the lock is reset. Here is the correct code is 2368.When press 2 on the flop first round (IC1A) will be activated and the value of the data (pin9) is transferred to the Q output (pin13). Since the pin 9 is based the value is "0" and therefore the pin 13 is low. For further press the digits of the code in the correct sequence is "0" leads to the Q output (pin 1) of the last flip flop (IC2b). This makes the transistor and relay energised.The automatic restoration facilities managed by the resistance R11 and capacitor positive C2.The final capacitor C2 is connected to the pin assembly flops.When filp-transistor is turned on , the capacitor C2 begins to charge as the voltage across it becomes enough top-flops are reset. This makes the lock of a fixed amount of time and then automatically locks. The delay time can be adjusted by varying the values of R11 and C2.
