number 5 (IC3 pin 10) from the knock selection 1 and number 7 (IC5 pin 5) from the knock selection 2, then first you have to knock 5 times to switch on the next circuit that is built around IC4 and IC5. The next circuit will switch ON for five seconds in these five seconds you have to knock seven times to provide the correct number to switch on the relay. If you have not provided the proper knock code to the first knock circuit (built around IC3 and IC3) then the second knock circuit will not become activated.

The circuit is built using five ICs. A peizo electric sensor is used to sense knocks. The knocks sensitivity can be adjusted with the 100K variable resistor. The LED used at the output of the IC2 blinks on each knock the circuit will receive. For best result attach the peizo at the back side of the place of knocks. For example if you are using this for your store room door then place the peizo at the back side of the door where you desired to knock.

The operating voltage of the circuit is 9V to 12V DC. The circuit can also be operated on lower voltages like 5V or 6V etc. The relay value should be according to the operating voltage.
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This is a project of an automatic knock sensing code lock circuit. The circuit requires two different codes to switch on the relay at the output. These two codes can be selected with the two selection points marked knock selection 1 and knock selection 2. For example if you have selected
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Knock Sensing Code Lock Circuit Diagram