Electronic Keypad Combination Lock

When wired to a ten-digit keypad, the circuit will recognize one 4 digit combination out of a possible 5040 codes. When the programmed four-digit combination is entered from the keypad, in proper sequence, LOCK turns on and Lock Status turns off. The lock combination is set by pins 3, 4, 5 and 6 on the LS7220. These correspond to the digits on the k

eypad. So if for example you wanted to set a combination of 8462, wire key 8 to pin3, key 4 to input 4, key 6 to input 5 and key 2 of the keypad to input 6. Any unused keys are wired to pin 2. An input on pin 2 resets the lock combination. The keypad must have individual connections for each key and a common return key. The return key is wired to pin 12 of the LS7220. The alternative is to wire a group of switches in parallel.

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