Home Security System

The purpose of this project is to add an element of security to the average household. The idea is to scare potential intruders away by sounding an alarm while they attempt to enter a house equipped with this system. The system is intended to be very precise and sensitive, while also being cost effective. The project is practical in that the user interface is very simple. The entire system can be controlled from a single console, and merely a few keystrokes are required to perform any of the system’s functions.

1.2 Functions

This system takes in a user pass-code to perform all of its actions. Using this pass-code, the user can arm and disarm the system. The user can also change the pass-code. The state of the system will be displayed using LEDs. It will display red for the arm state, green for the disarm state, and yellow for the pass-code changing state. While the system is in the arm state, the system alarm will sound if any of the break-beam sensors are tripped. The alarm can only be disabled by entering the correct user pass-code. The system will also automatically clear an incorrect pass-code once it is fully entered.

1.3.1 Power Supply

The supply provides dual 5 volt DC outputs. One of the outputs is dedicated to the break-beam sensors and the Piezo horn, and the other output supplies the rest of the components.

1.3.2 HC12 Microcontroller

The HC12 controls what state the system is in. It takes inputs from the keypad. It outputs to the LCD to show when the keypad is being pressed. It also outputs to the three state LEDs.

1.3.3 Keypad

The 16-Key keypad allows the user to control the system. It is coupled with a decoder that communicates with the microcontroller directly.

1.3.4 LCD

The LCD displays a ‘*’ whenever a key is pressed on the keypad. This is simply to show a response to user input. Another function that the LCD serves is its auto-clear function. If all 6 digits of the pass-code have been entered and they are incorrect, the LCD clears the screen.

1.3.5 Sensors 

The sensors used in this system are infrared emitter-detector pairs. They output a voltage HI when the beam is broken. TTL logic is used to configure these sensors with the state indicating LEDs. The output of that logic is sent to the alarm.

1.3.6 Alarm

A Piezo horn is used as an alarm for the system. This horn is sufficient for the prototype. In a real world setting, this horn can be easily replaced with a higher outputting horn. The alarm is turned on by logic output of the sensors and the state indicating LEDs. 

2.1 Power Supply

The block diagram for the power supply is shown in figure 2a below. This configuration allows the system to be plugged into any standard wall socket.

Figure 2a

The circuit diagram for the power supply is shown in figure 2b. An important characteristic of this diagram is the use of two 7805 regulator chips. These chips provided the dual outputs that were needed to power the system properly.

Figure 2b