In this post we try to analyze a simple door lock circuit using digital code that needs to pressed with a unique sequence in order to activate the door lock system and unlock it.
Anyone who has ever locked him or herself out with the front door key inside will appreciate the electronic door-opener described here. If you can memorize four digits in a row and do not mind an investment in an electric door-opener and a small electronic circuit, you will never need a front door key again. The locked door can be opened by pressing the keys on a keyboard fitted beside the door, and the door unlocked instantly as soon as the right set of code were pressed on the keyboard.
The complete circuit of the proposed door lock circuit using digital code is configured around the IC LS7220.
Its pin numbers 2 to 6 are wired across the 10 keypad button through a special arrangement so that pressing only a the selected sequence of the code on the 0 to 9 buttons activates the output of the IC.
Basically pins numbers 3 to 6 enable the correct code sequence.
In this door lock using digital code circuit the keypads can e seen attached with the IC pinouts in the format: 4179