ir burglar
TRANSCRIPT
CIRCUITIDEAS
E L E C T R O N I C S F O R Y O U • J A N U A R Y 2 0 0 6 • 1 0 1W W W . E F Y M A G . C O M
CMYK
Fig. 2: Pin configurations of UM3561 and TSOP1738
Fig. 1: Circuit for IR burglar deterrent
Thwart any burglary attempt us-ing this infrared proximity de-tector that triggers an alarm
when the rays falling on its sensor areinterrupted.
The circuit of IR burglar deterrent(shown in Fig. 1) comprises transmit-ter and receiver-cum-alarm sections. Itworks off 6V DC, 500mA uninter-rupted supply and uses low-cost
T.K. HAREENDRAN
IR BURGLAR DETERRENT S.C. DWIVEDI
readily-available electronic compo-nents. LED2 is used for indicatingpower-‘on.’
The transmitter section is builtaround timer 555 (IC1), while the re-
ceiver-cum-alarm section con-sists of IR sensor TSOP1738,dual precision monostablemultivibrator CD4538 andthree-siren sound generator ICUM3561. Pin configurations ofUM3561 and TSOP1738 areshown in Fig. 2.
The astable multivibrator(IC1) oscillates at a frequencyof around 38 kHz, which istransmitted by the infraredLED (IR LED1). Resistor R2limits the current across the IRLED.
The transmitted IR signal directlyfalls on IR sensor TSOP1738. When-ever the IR signal is interrupted, itsoutput pin 3 goes low and IC2 is trig-gered at pin 5 through transistor T2.As a result, its output at pin 7 goeslow (for a preset time) to forward bias
siren-driver transistor T2. This condi-tion is indicated by the glowing ofLED1. The time-out period can be in-creased or decreased by changing thevalue of capacitor C6.
Now siren-sound generator IC3 isactivated and its output signal is am-plified by transistor T4 to produce asound resembling that of police siren.Resistor R14 limits the loudspeakercurrent.
The output tone of siren-soundgenerator IC3 can be set by connect-ing its pin 6 to either Vcc or GND.When you connect pin 6 to Vcc IC3produces the sound of fire-alarm si-ren, but when you connect it to GNDit produces the sound of ambulancesiren.
Assemble the transmitter and re-ceiver-cum-alarm circuits on two sepa-rate general-purpose PCBs and housein suitable cabinets. Mount the unitson the opposite sides of the entrancegate such that IR rays from IR LED1fall directly on the IR receiver module(TSOP1738).