Previously PIR based alram circuit was demonstrated. Here a simple IR sensor-based alarm system built using an IR sensor module, two BC547 NPN transistors, a 1 kilo-ohm resistor, and an active buzzer is illustrated.
The IR sensor module is powered using a 5V supply. Its Vcc pin is connected to the +5V rail and its ground pin is connected to the ground rail of the breadboard.
The output of the IR sensor module is connected to the base of the first BC547 transistor. The collector of the first transistor is connected to +5V, and its emitter is connected to the base of the second BC547 transistor.
The second BC547 transistor has its emitter connected to ground. Its collector is connected to the negative terminal of the active buzzer, while the positive terminal of the buzzer is connected to +5V.
When no object is detected, the IR sensor output remains LOW. Therefore, no base current flows into the first transistor. As a result, both transistors remain OFF, and the buzzer does not sound.
When an object is detected, the IR sensor output goes HIGH. This HIGH signal provides base current to the first transistor, turning it ON. Current then flows from its collector to emitter, supplying base current to the second transistor.
The second transistor then turns ON and provides a ground path for the buzzer. Current flows from +5V through the buzzer and through the second transistor to ground.
Since an active buzzer contains an internal oscillator circuit, it immediately produces sound when powered.
Thus, the circuit works as a simple object detection alarm using two transistors as switching and amplification stages.
Video demonstration of this IR sensor alarm is below.
