The project shows you how to build a combination lock for your home door using PIC16F84 MCU and electro-magnetic lock. A 4×4 keypad, located outside the door, is used to enter key combination. The master combination will open the door, as well as allow programming of up to four transient combinations, the illumination duration, and lock solenoid duration. The lock solenoid is activated for a programmable time (initially one second) when the correct six-digit combination is entered on the keypad, or when the MANUAL pushbutton is pressed inside the building.
Any time the lock solenoid is activated, the illumination relay is activated for a programmable time (initially five seconds.) The relay can control sidewalk or keypad illumination lamp connected to an appropriate voltage. A DISABLE switch, located inside the building, is useful for day use when the building is occupied. The programmed values are stored in the MCU’s EEPROM. Setting a value to all zeros deactivates it. Project’s schematic and source code.