This document describes the design of an infrared intruder alarm system with a transmitter circuit that uses an IC 555 astable multivibrator to produce a 38kHz modulated IR signal transmitted up to 15 feet. The receiver circuit uses a TSOP1738 sensor that responds to the 38kHz signal, and triggers a CD4011 flip-flop circuit connected to a piezo buzzer alarm when the IR path is interrupted. The system is intended for uses like home security, vehicle security, and other property protection applications.
4. TRANSMITTER THEORY
The transmitter section is built around IC 555 (IC1),
which is wired as an astable multivibrator.
It produces about 38kHz frequency.
IR LED1 emits 38kHz modulated signals up to a
distance of 4.6 metres (15 feet).
The modulated IR beam from the transmitter
continuously falls on the receiver section.
6. RECEIVER THEORY
The receiver sensor TSOP1738 responds to
38kHz frequency.
The modulated IR beam falling on receiver
sensor TSOP1738 makes its output low.
When somebody crosses the path of IR rays it
senses this and its output goes high momentarily,
which triggers the flip-flop.
In the reciever circuit the flip-flop circuit uses IC
CD4011.
The IR transmitter and receiver units are
mounted opposite to each other on the sides of
entry door or gate.
7. LIST OF PARTS
Semiconductors:
D1 - 1N4148
IRLED1 - Flat LED
ZD1 -5.1 volts
IC1 -NE555
IC2 (N1-N2) -CD4011
Resistors:
R1 - 6.8 K ohm
R2 - 100 K ohm
R3 - 10 K ohm
R4 - 18 ohm
R5 - 150 ohm
R6 - 22 kilo ohm
R7- 270 K ohm,
0.5 watt
R8 - 10 K ohm
R9- 680 ohm
Capacitors
C1- 100 µF, 16 volt
C2 - 220 pF
C3- 0.01µF
C4- 100 µF, 16 volt
C5- 6.8 µF, 16 volt
Miscellaneous:
S1- ON/OFF switch
PZ1 (Piezo buzzer)