Arduino Alarm System - Gauanglong Hu¶
Problem
I had a very bad experience of burglary when I was a sophomore in undergraduate school about four years ago. I thought where I was living was a very safe place and I did not have a habit to lock the door. When I was reviewing for the exam in the morning about 2 am midnight, someone entered my room and tried to steal something. Fortunately, the person saw me awake and he fled immediately and nobody was hurt. This experience had haunted me for about two years and I could not fall asleep if I did not check whether the door was locked and with a baseball bat beside my bed. Moreover, there are some violence and crimes against specific ethic group. There was a song called “Meet the Flockers” by YG. The lyric is a standard operation procedure to motivate people how to rob a Chinese people. After the song was published, there have been some fatal home invasions targeted Chinese residential area. However, the most important thing is that I cannot possess a fire arm legally as a legal immigrant. Therefore, an alarm system will become helpful. It can generate high pitch sound to wake me up and also possibly scare burglars away. It can also mimic the light effect on police vehicle.
Methods
The alarm system was built using a distance sensor, a piezo buzzer, a blue LED, a green LED, a red LED, Sparkfun red board, and a bread board. The alarm system is shown in Figure 1 and the schematic shows the connection in Figure 2. The method to detect whether someone have broken in is to put the alarm system somewhere near the door and it will detect the distance between the distance between the door and the system itself. If the distance is smaller than the previously specified value in the code, the alarm will be triggered.
Figure 1. Arduino alarm system
Figure 2. Connection of Arduino alarm system
Challenge
The challenge I encountered in this project is that I did not know how does the distance sensor worked. As shown in Figure 3, the distance sensor is a SR04-Ultrasonic Distance Measurement Sensor and it has four different pins. The GND and Vcc are used to connect to the GND and 5-volts power supply portal on the Sparkfun red board. The “Trig” pin is used to command the sensor to send sonar signal to objects in front of it. The “Echo” pin is used to receive the signal reflected back from the objects and record the time consumed for the signal to come back after it was sent.
Figure 3. SR04-Ultrasonic Distance Measurement Sensor
How it works
After the code is uploaded to the Sparkfun red board, the green light is on to indicate that the alarm system is armed. If an object is put in front of it and the distance is smaller than the specified value in the code, the alarm will be triggered. The piezo buzzer will generate high pitch voice at a specified frequency and blue and green light will flash. The state machine diagram is shown in Figure 4.
Figure 4. State machine diagram of Arduino alarm system.