Gen Masuda Xuefan Zhang built an ultrasonic security system for their final project by our housing situation this summer. Security is an important part of home, especially if we are going to share a house with prior strangers without a lock on our room door.
Overview The system uses ultrasonic sensor that has a transmitter part and a receiver part. The ultrasonic transmitter periodically emits ultrasonic signals into an open area in front of it. To cover a wide range, a rotating servomotor is used to allow the sensor (transmitter and receiver pair) to cover roughly 180 degrees. If the signal ever hits a physical object, it will be reflected back and, the receiver part of the sensor will then capture it with the object considered detected as its position (distance from the device and angle relative to the device) is now known. As the security system sends off a sound alarm, the object position is polled by our MATLAB script, which then plots it on a graph and log the record. The record log is also sent as an email to an address set by the owner in advance.
From the user's perspective, here is the flow of the system: LCD indicates user may press the button "A" to start. After user presses "A", the LCD further asks user to set up a password that could be used to disable the security system later, followed by the button "#". After the user finishes entering the password, the password is stored for the session, and the security system becomes active: motor starts rotating, sensor is scanning for potential intruders within a distance (15 cm for our demo, but could be anything realistically. It is only constrained by the sensor range, which is 5 meters theoretically), and in the case that an object is detected, the system beeps and triggers MATLAB to send an email containing the time of detection to the user. If the user wishes to disable the security system, he or she could type in the password used to set up the session. LCD will then indicate session is ending, and a new session is started in 2 seconds.