Digital Combination Lock Circuit Schematic Diagram

This simple digital combination lock uses IC LS7220. The output of this circuit can be connected with relay as an ON/OFF control to the electronic devices. This circuit works with 5-12V power supply. To store the combination, connect the IC push button switch with the pin 3,4,5, and 6. For an example, S1 with pin 3, S2 to pin 4, S3 to pin 5, and S4 to pin 6. This will result 1234 combination. Connect S5-S8 with pin 2. This will cause to reset the IC if the combination is wrong. Relay will turn to active when the combination is correct. Here is the schematics :

Digital Combination Lock Circuit Schematic

Digital Combination Lock Schematic Diagram

Components :
Diode D1 : 1N4148
Volt regulator IC : LM317
Polar capacitor C1 : 1 uF/25V
Polar capacitor C2 : 220 uF/25V
Resistor R1 : 2.2k ohm/4 W
Resistor R2 : 1k2 ohm
Transistor Q1 : 2N3904
IC1 : LS7220
S1-S12 switch : push button
SPDT relay : 12 V
12 V power supply

Estimated price : $5

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