Combination lock in Electronic using LS7220

Description
This is the circuit diagram of a combination lock electronic simple using CI LS7220.This circuit can be used to activate a relay to control (the & off) press any device when a preset combination of 4 digits.The circuit can be operated from 5V to 12V.
Specify connection combination the appropriate parameters to pin 3, 4, 5 and 6 IC through the head.As an example, if S1 is connected to pin 3 to pin 4, S2, S3, S4 to pin 5 to pin 6 IC, will the combination be 1234. This way we can create all the 4 digit combinations.Then connect the rest of the parameters to the leg 2 of the IC.This will cause IC reset If an invalid key is pressed, and the whole key code has to be entered.
When the right key is pressed, the out put (relay) for a period of time is determined be enabled by the capacitor C1.Here, it should be 6s.Temporary increase increase C1.
On the key pad, arrange switches in a 3 X 4 matrix on PCBs. Write the digits keys using a pointer instead of numbers.


Circuit Diagram


Circuit Parts Details
  • C1 1-Capacitor electrolytic 1uF 25V
  • C2 1-220uF 25V Electrolytic Capacitor
  • R1 1-2.2 K 1/4W resistor
  • Q1 1-2N3904 npn Transistor 2N2222 
  • D1 1-1N4148 diode rectifier 1N4001-1N4007
  • K1 1-12V SPDT Relay Any appropriate relay with 12V coil
  • U1 1-IC LS7220 Digital lock 
  • S1-S12 12 SPST momentary Pushbutton keyboard (see notes)
  • HD1 1-12 position Header




Pin Details of LS7220





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