Security Lock with keypad and LCD (PIC16F84A)

  
Finally I was able to control an LCD Hitachi display and a 12-key matrix keypad with only one 16F84 or 16F628. In a near future, I will be able to control a full QUERTY-type keyboard and a LCD display. The biggest improvement on this projects was the compatibility with the Microchip PIC 16F84 and the 16F628, also the 16x1 or the 8x1 LCD Hitachi can be used. To reduce the cost of this proyect, is possible to remove the LCD and the circuit will work with the beep codes. Basically, the hardware is a mini-terminal controlled by a 16-pin PIC.
Security Lock with keypad and LCD (PIC16F84A) - schematic

As you can see, the 3x4 keypad uses only 4 I/O ports. To determine what key is pressed, I read the discharge time of each capacitor. This is a new technique that I developed since two years ago but finally I was able to test it successfully. The only inconvenience of this method is the reading from the keypad is affected by the voltage of the circuit. Anyway, the circuit needs exactly +5V because the LCD. The switch labeled as "Toggle" and "Normal" defines the function of the security keypad. With the "Toggle" setting, the "Enable Signal" will toggle each time the correct password is entered. With the "Normal" setting, each time when the correct password is typed, the "Enable signal" will be ON for only four seconds. Activate an electric or electronic device enable by the signal. Example: A car or any electric machine cannot be turned on until the correct password is provided. To enable or disable a central alarm. Keep a circuit ON or OFF that requieres authorization. (Maybe to keep children without TV until the homework is donde). Security vault - Input the code and an electromagnet will be enable during 4 seconds allowing to open the door. Security entry port - Only authorized employees can input the code enabling the electromagnetic door lock for 4 seconds. Enable a circuit with one pulse to toggle it.




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