This electronic device is designed to alert the user to an intrusion. The project consists of a sensor and a control unit which are connected to each other. The sensor detects the interruption whenever an object or person comes between its transmitter and receiver. This interruption results in a signal generation which is supplied to a speaker.
This way whenever an intrusion takes place, the speaker goes on. Such devices are installed at various locations in houses or offices, especially near doors, windows.
In this project, the transmitter part of the circuit is an Infrared (IR) Led which transmits continuous IR rays to be received by IR receiver. The reception of rays at IR receiver results in high voltage at the output. The output of this IR sensor remains low when no signal is received.
The output of IR sensor is connected to the Reset pin (Pin 4) of NE555 in accordance to the push-pull concept. The Reset pin of NE 555 is active low, i.e., the output of NE555 remains low (0V) when the input voltage is low, regardless of the threshold voltage. The output frequency can be adjusted by different value combinations of resistors R1, R2 and capacitor
The transmitter and receiver are placed such that an interruption is observed when the receiver receives reflected IR rays. In this case, the output of sensor and therefore the Reset pin remains high. Under such condition NE555 starts generating pulse of certain fixed frequency. The output of NE555 is filtered by a capacitor C2 (1uF) and fed to a speaker. Many sensor modules can be installed at different locations in a house or office and their outputs can be used to feed the Reset pin of a common NE555. Whenever any of the sensors detect the IR pulse, the RESET pin will go high and eventually the speaker will produce sound.
Filed Under: 555 Timers, Electronic Projects