03-02-2012, 03:51 PM
WIRELESS SWITCH
Normally, home appliances are
controlled by means of switches,
sensors, etc. However,
physical contact with switches may be
dangerous if there is any shorting.
The circuit described here requires
no physical contact for operating the
appliance. You just need to move
your hand between the infrared LED
(IR LED1) and the phototransistor
(T1). The infrared rays transmitted by
IR LED1 is detected by the phototransistor
to activate the hidden lock, flush
system, hand dryer or else.
This circuit is very stable and sensitive
compared to other AC appliance
control circuits. It is simple, compact
and cheap. Current consumption is
low in milliamperes.
The circuit is built around an IC
CA3140, IRLED1, phototransistor and
other discrete components. When regu-
Navpreet Singh Tung
WIRE LESS SWIT CH s.c. dwivedi
lated 5V is connected to the circuit, IR
LED1 emits infrared rays, which are
received by phototransistor T1 if it is
properly aligned. The collector of T1
is connected to non-inverting pin 3 of
IC1. Inverting pin 2 of IC1 is connected
to voltage-divider preset VR1. Using
preset VR1 you can vary the reference
voltage at pin 2, which also affects sensitivity
of the phototransistor.
Op-amp IC1 amplifies the signal
received from the phototransistor.
Resistor R3 controls the base current of
transistor BC548 (T2). The high output
of IC1 at pin 6 drives transistor T2 to
energise relay RL1 and switch on the
appliance, say, hand dryer, through the
relay contacts.
The working of the circuit is simple.
In order to switch on the appliance,
you simply interrupt the infrared rays
falling on the phototransistor through
your hand. During the interruption,
the appliance remains on through the
relay. When you remove your hand
from the infrared beam, the appliance
turns off through the relay.
Assemble the circuit on any general-
purpose PCB. Identify the resistors
through colour coding or using the
multimeter. Check the polarity and pin
configuration of the IC and mount it
using base. After soldering the circuit,
connect +5V supply to the circuit.
