circuit

ideas

w w w . e f y m a g . c o m electronics for you • m a r c h 2 0 0 8 •   10 3

This infrared obstacle-detector

can be used not only with line-

following robots but also as apart of home/shop automation.

The circuit uses an infrared trans-

mitting LED (IR1) and an infrared

receiving diode (IR2). It works off a5V DC regulated power supply. A

short invisible light beam transmitted

by IR1 when reected from an obsta-

cle or object is received by IR2. Upondetecting the obstacle, the circuit gets

activated and turns on an aural alert

circuit for a few seconds. The alarm

sound is produced by loudspeakerLS1. Visual power-‘on’ indication is

provided by an ordinary red LED

(LED1). The home-made sensor con-

sisting of IR1 and IR2 is at the heart ofthe circuit. Alternatively, you can use

an integrated opto-reective sensor

(CNY 70).

Here, IC1 is wired as an astablemultivibrator with adjustable pulse

width, ranging from 1 millisecond to

10 milliseconds with component values

of VR1, R1, R2 and C1 as shown in Fig.

T.K. Hareendran

Ir ObsTacle-deTecTOr FOr rObOTs

 s.c.  d w i v e d i

1. Use multiturn preset potmeter VR1to set the output pulse width. The out-

put pulses from IC1 drive the infrared

transmitting LED (IR1) through low-

power transistor T1. Resistor R4 limitsthe input current of IR1 sensor.

When the reected infrared light

beam falls on IR2, current flows

through resistor R5, which produces apositive voltage at the base of transistor

T2 to make it conduct. When transistor

T2 conducts, alarm-driver transistor

T3 remains forward biased until theobstacle is cleared, i.e., it goes out of

the sensing range.

When transistor T3 conducts, asta-

ble multivibrator CD4047 (IC2) is ena-bled by the high signal at its pin 5. IC2

needs only two external components

(R8 and C3) to oscillate. The audio

signal output from IC2 is ampliedby Darlington pair of transistors T4

and T5. Resistor R10 limits the current

Fig. 1: IR obstacle detector 

Fig. 2: Home made sensor mounting

through the loudspeaker (LS1).Assemble the circuit on any gen-

eral-purpose PCB and house in a

suitable cabinet. Connect the sensor

through the external wires and x itaccording to your requirement at a

suitable place. In robotic applications,

the high-level output available at the

emitter of transistor BC548 (T3) canbe used to control relay/motor-driver

circuits of the machine.

 Notes. 1. The circuit can detect ob-

stacles up to a distance of 10 cm whenthe sensor and the obstacle are proper-

ly aligned. The range mainly depends

on the reecting properties of obstacles

and the type of the opto-reective sen-sor LED used in the circuit.

2. The home-brewed sensor ar-

rangement is shown in Fig. 2.