Only people who know the set code can open the gate with this simple key- operated locking system. To make the motor in the gate work, you have to type the code into the keypad within the time limit. If someone tries to open the gate and presses the wrong key on the keypad, the system is turned off and an alarm goes off to let you know someone has broken in. Fig. 1: Block diagram of simple key-operated gate locking system The block diagram of the key-operated code locking system can be seen in Figure 1, and the circuit diagram can be seen in Figure 2. Establish connections between the keypad's various points and the circuit's points A, B, C, D, E, and F, as well as ground. Here, the S7, S16, S14, and S3 keys are used to enter the code, and the other keys are used to turn off the system. To make the code, it is very important to press the keys in that order. Press the switches S7, S16, S14, and S3 in order to start the motor of the gate. If the keys are pressed in a different order than what was set, the system will automatically lock and the motor will not start.

Fig. 2: Circuit of simple key-operated gate locking system At first, pin 14 of AND gate IC6 doesn't have 6V, so no pulse gets to the base of npn transistor T1 to set off timer IC5, so the gate doesn't open. To turn on the system, you must first turn on IC4. When the switch S7 is pressed, the timer IC4 sends 6V to IC6 for about 17 seconds. You have to press the switches S16, S14, and S3 in order during this time. Because of this, the outputs of timers IC1, IC2, and IC3 go high in order. These high outputs are then sent to gates N1 and N2 of IC6 to trigger IC7 through npn transistor T1. IC1, IC2, and IC3 are all set to have high outputs for 13.5, 9.43, and 2.42 seconds, respectively. When all four switches (S7, S16, S14, and S3) are pressed in order, timer IC7 starts the motor for the amount of time that was set, which opens the gate. When the time is up, the motor stops by itself. Adjusting preset VR5 lets you choose how long the motor is "on." Here, the shortest time it can be "on" is 5.17 seconds, and the longest time it can be "on" is 517 seconds. If a switch other than S7, S16, S14, or S3 is pressed, IC5 is triggered to turn on relay RL1, which cuts power to the second relay. This locks the system and

makes the piezo buzzer PZ1 sound, so you know someone is trying to open the gate lock. Now, press any key on the keypad (except S7, S16, S14, and S3) to turn off the sound and reset the system. The circuit runs on a regulated 6V DC power supply and is easy to put together on a PCB for general use.