8/13/2019 Anti Theft Alarm for Bikes_opt

1/1

C I R C U I T I D E A S

ELECTRONICS FOR YOUOCTOBER 2004

S . C . D W I V E

D IANTI-THEFT ALARM FOR BIKES

PRAVEEN KUMAR M.P.

I f anybody tries to steal your bike, thiscircuit turns on the horn of the bike toalert you of the impending theft.Usually, a handle lock is used on the

handle bar for the safety of bikes, withthe front mudguard in a slanted position.

When the handle lock is freed, the frontmudguard can be aligned with the bodyof the bike.

This circuit consists of transmitter andreceiver sections. The transmitter (IRLED1) is fitted on the back end of thefront mudguard and the receiver sensor(IRX1) is fitted on the central portion of the crash guard of the bike such that IRrays from the transmitter directly fall onthe sensor when the front mudguardcomes in line with the body of the bike.

The transmitter section is built aroundtimer 555 (IC2), which is wired as an astablemultivibrator with a frequency of around38 kHz. The output of IC2 is further ampli-fied by transistor T1 and given to an infra-red light-emitting diode (IR LED1), whichcontinuously transmits the IR frequency.

The receiver section uses IR receiver

module TSOP 1738 (IRX1), which is nor-mally used in TV receivers. The receivermodule senses the IR modulated frequencytransmitted by the IR LED.

When no IR rays are incident on thesensor, its output is high. But the output of the IR sensor goes low when it senses themodulated IR signal. The output of the

receiver module is given to a negative-voltage comparator built around IC LM311(IC3). The input voltage at pin 2 of IC3 isfixed by using the voltage-divider networkcomprising resistors R7 and R8.

When IR rays are not incident on the IRreceiver module, the voltage at pin 3 of IC3is greater than the voltage at pin 2. As aresult, the output of comparator IC3 is low.But when the receiver senses IR rays fromIR LED1, the voltage at pin 3 of IC3 is lowerthan the voltage at pin 2. As a result, theoutput of the comparator goes high.

The output of the comparator is givento a latch made up of JK flip-flop (IC4). Thelow-to-high going pulse from the compara-tor makes the output of IC4 high until it isreset. The output of IC4 is latched and usedto energise relay RL1 via transistor T2. Therelay is connected to the negative terminal

of the mobikes horn, while the positiveterminal of the horn is connected to thepositive terminal of the battery via resistorR1. The energised relay drives the horn,which continues sounding until you pressreset switch S2 momentarily.

At night, lock your bike using thehandle lock and switch on the circuit us-

ing switch S1. Since the IR transmitter (IRLED1) and the receiver (IRX1) will not bein line of sight, IR rays from IR LED1 willnot be incident on the sensor. When any-one tries to move the bike away, the IRtransmitter and the IR receiver will comein line of sight and the IR rays from theIR transmitter will be incident on the re-ceiver. This will make the output of thecomparator (IC3) high. The pulse from thecomparator will make the output of latchIC4 high and transistor T2 will conduct tosound the horn via relay RL1.

Note. The circuit excluding the trans-mitter and the receiver can be housed ina small metal box and kept inside the toolbox of the bike.

Before you start your bike, makesure that the circuit is switched off usingswitch S1.

www.eeecube.com - Distributed for educational purpose only -Copyrighted to EFY MAG

http://www.eeecube.com/http://www.eeecube.com/http://www.eeecube.com/