Simple Electronic Combination Lock circuit diagram

Posted on Feb 5, 2014

This could be the circuit diagram of a easy electronic combination lock by using IC LS 7220. This circuit may be applied to activate a relay for controlling (on & off) any device each time a preset combination of 4 digits are pressed. The circuit may be operated from 5V to 12V. To set the mixture connect the appropriate switches to pin 3, 4, 5 and 6 o

Simple Electronic Combination Lock circuit diagram
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f the IC through the header. As an example if S1 is connected to pin 3, S2 to pin 4, S3 to pin 5, S4 to pin 6 of the IC, the combination is going to be 1234. This way we can create any 4 digit combinations. Then connect the rest of the switches to pin 2 of IC. This will cause the IC to reset if any invalid key is pressed, and entire key code has to be re entered. When the correct key combination is pressed, then the output ( relay) will be activated for a preset time driven by the capacitor C1. Here, it is set to be 6S. Increase the value of C1 to increase the preset time. For the keypad, arrange the switches in a 3X4 matrix on a PCB (Printed Circuit Board). Write the digits on the keys by using a marker. Instead of applying numbers I wrote some symbols!. The bad guys is going to be more confused with this.

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