Plastic Infrared Burglar Alarm Circuit, For Office Security, Feature : Durable

Infrared Burglar Alarm gives alarm on interruption of IR beam. The entry of undesirable person from the gate produces an alarm which is much more pronounced and the alarm can be either fitted inside the house or outside as desired. By using this circuit, residents need not spend on watchdog or watchman to restrict the entry of unwanted elements. This IR circuit i.e. transmitter and receiver is mounted on two side of gate. The intruder while passing through the gate obstructs the IR (non visible) beam and produce a remote alarm to be fitted as desired by the house owner.
About the circuit :

• The transmitter IC 555 wired in astable mode provides the pulsed power to IR LED D4. The frequency is settable with the help of P3, R10 is current limiting resistor. IC 555 is economical element to make this circuit. Since the modulated high pulse power enables long range sensing, it is common practice to pulsed IR technique.
• IR LED D4 transmits the modulated light which falls on receiver which is kept aligned with transmitter. Alignment accuracy need not be very high and minor misalignment may not produce any malfunction. Receiving IR module IRX receives IR light energy and produces electrical pulses its output. These pulses are buffered and inverted by transistor T1. Now these low going pulses triggers a monostable ckt based on IC2 which is again a 555 IC. The frequent triggering and retriggering produces D.C. output at pin 3 of IC2. P1 is provided to adjust the monostable timing such that output at pin 3 is continuously Hi (IR pulses retrigger the monostable before mono output goes low after expiry of its timing). This output is fed to a melody generator IC 3 (UM66). Pin 2 of IC is a supply pin and when IC2 output is Hi, IC3 gets supply through 3.3V zener and produces melodious output through the speaker and driver transistor T2.
• IC2 power is regulated through a 5 volt regulator so that its output will not give undesirable level above 5 volts and save D3 zener as well as IC3.
• The power input for regulator is derived from centretapped transformer 6-0-6 rectifier and filler is provided on board.
• The transmitter is powered from a 9V battery.