A very simple electronic combination lock based on IC LS7220

The picture below is a very simple electronic combination lock based on IC LS7220.

Component parts list:

C1 = 1uF 25V

C2 = 220uF 25V

R1 = 2.2K ohms

Q1 = 2N3904 / 2N2222

D1 = 1N4148 / 1N4001-1N4007

K1 = 12V SPDT relay/any suitable relay with 12V coil

U1 = LS7220 digital lock IC

S1-S12 = SPST momentary buttons? Keyboard (see notes)

HD1 = 12-bit header

Circuit notes:

This could be the circuit diagram of a simple electronic combination lock using IC LS 7220. This circuit can be used to activate a relay to control (turn on and off) any device every time a preset 4-digit combination is pressed. This circuit can operate from 5V to 12V.

To set up the mixing, connect the appropriate switches via headers to pins 3, 4, 5 and 6 of the IC. For example, if S1 is connected to pin 3, S2 to pin 4, S3 to pin 5, and S4 to pin 6 of the IC, the combination will be 1234. This way we can create any 4-bit combination. Then connect the remaining switch to pin 2 of the IC. If any invalid key is pressed, the IC will reset and the entire key code must be re-entered.

When the correct key combination is pressed, the output (relay) is activated for a preset time, driven by capacitor C1. This is set to 6S. Increase the value of C1 to increase the preset time.

For the keyboard, arrange the switches in a 3X4 matrix on the PCB (Printed Circuit Board). Use a marker to write the numbers on the keys. I wrote some symbols instead of numbers! The bad guys will be even more confused with this.