CODE LOCK

Electronic code lock with the ability to rewrite the entry code. Can be used for entrance door, car door or a locker. Any 4 digits number can be used (the digit 0 is not used). Using microcontroller PIC16F628A programmed with the downloadable assembly and C source code. To change the 4 digits code press 'code change' switch, the LED will indicate ready state, press the 4 new digits, the LED will switch off. The code changing switch has to be mounted in a hidden area. There is a max 5 seconds delay between pressing any two digits, after the 5 seconds delay the 4 digits code has to be re-entered. The 4 digits are stored in the chip's EEPROM, so the numbers are retained when the power is off.

Software includes PIC code. You are free to use the circuit diagram and the software with no

Circuit Description
See also Technical Tips

78L05 is the regulator for the IC. The 12V supply is for the relay, you can use 24V relay and supply voltage.
Key pad can be any matrix switches. The on resistance 1K max. The digit 0 is not used.

The EEPROM retains the code when the power is off.
330K resistor determine the microcontroller frequency, increasing the value will decrease the frequency hence increasing the 5 seconds delay.