infrared bodyÞtector

INFRA-RED BODY DETECTOR - M3)T SffWTMn)

THE circuit in Fig.2 can detect any large object which appears in front of the sensor, IC1. This device is an infra-red remote control receiver and a vaÅ„ety of types can be used, including the readily available IS1U60.

The heart of the circuit is the NE567, IC2, a tonÄ™ decoder which produces a logie 1 out-put at pin 8 when the frequency at its input pin 3 is equal to that produced by its internal oscillator. The oscillator’s frequency is set by resistor R2 and capacitor C5. It is output from pin 5 and fed via resistor R3 to one input of NAND gate IC3c, pin 12.

NAND gates IC3a and IC3b are configured as an oscillator whose output at IC3b pin 4 Controls the other input of IC3c, pin 13. The mod-ulaled output from IC3c pin 11 is fed to tran-sistor TRI via buffer resistor R8. This causes the two infra-red l.e.d.s D3 and D4 to tum on and off in response to the modulated signal. Their output intensity is adjustable by preset VR1. Components R9 and C8 filter ripple volt-ages produced across the l.e.d.s and also inerease the peak current flow through them.

Preset VR1 is used to set the desired detec-tion rangÄ™. With its resistance set at 10£1 if a large object, such as a human body, approaches the circuit within two metres, IC2 pin 8 will go high. The output is fed to the network Dl, R4, R6 and C7, which filteis the signal to ensure that random noise does not affect the circuit. The network feeds into IC3d whose output when high turns on l.e.d. D2 via buffer resistor R7.

You can also use IC2 output pin 8 to control other circuits, as part of a thief alarm or automatic door-opener, for example.

Hein Myo Latt, Yangon, Myanmar

Fig.2. Circuit diagram for a novel Infra-Red Body Detector.