IR Based High sensitive Door Security Alarm circuit diagram
This IR based security Alarm circuit is high sensitive . Here A Photo transistor L14F1 is used for detection of IR rays.
555 timer ic is used to provide a pulsed output For Emitting of IR rays at specific Frequency. First part of IR Security Alarm circuit including 555 ic and IR LED. This section transmit A Specific Frequency For IR LED.
Next stage of circuit including a comparator ic 358. The Photo transistor is connected with non inverting input of this ic. Base pin of Phototransistor is not connected with circuit. The output of ic 358 is directly connected with the other 555 timer ic which is arranged in Monostable mode to give an output to Buzzer for fix duration.
When light fall on base junction of phototransistor then it produce an inverse current and voltage between base and emitter, so at first when there is no any interruption between IR LED and Photo-transistor, the IR light falls on that . Then The voltage at non-inverting pin of comparator is smaller than inverting input (LOW). And if voltage at non-inverting(Pin3) is Low than the inverting the Output of its at pin 1 is HIGH (+vcc).
When any Interruption ocuur between IR LED and Phototransistor then the voltage at pin no 3 which is higher than the inverting input voltage, at this condition the output At Pin 1 is LOW (-vcc). This LOW voltage Trigger the 555 ic (u3). And after triggering of this ic the output at pin 3 of 555 is HIGH. Here High Output is for a fix duration because of Monostable connection is connected .
This HIGH output of 555 (u3) Turns on the Transistor Q1 . After transistor activating, it Switch on the connected Buzzer . You can connect Light with the use of relay with the transistor.