Electronic Combination Lock Circuit using IC LS 7220

Posted on Feb 6, 2014

This is the circuit diagram of a simple electronic combination lock using IC LS 7220. This circuit can be used to activate a relay for controlling (on & off) any device when a preset combination of 4 digits are pressed. The circuit can be operated from 5V to 12V. To set the combination connect the appropriate switches to pin 3, 4, 5 and 6 of the IC th

Electronic Combination Lock Circuit using IC LS 7220
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rough 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 will 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 the out put ( relay) will be activated for a preset time determined by the capacitor C1. Here it is set to be 6S. Increase C1 to increase on time. For the key pad, arrange switches in a 3X4 matrix on a PCB. Write the digits on the keys using a marker. Instead of using numbers I wrote some symbols!. The bad guys will be more confused by this.

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