Wireless On-Off Switch

Small and simple circuit, Suitable for home appliances

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 (D2) and the
phototransistor (Q1). The infrared rays transmitted by D2 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, D2, phototransistor and other discrete components.

Circuit diagram:

Wireless on off Switch

Wireless on-off Switch


R1 = 470R
R2 = 100K
R3 = 3.3K
R4 = 10K
D1 = 1N4007
Q1 = L14F1
RL = 5Vdc Relay
IC = CA3140
Q2 = BC548

Circuit Operation:

When regulated 5V is connected to the circuit, D2 emits infrared
rays, which are received by phototransistor Q1 if it is properly
aligned. The collector of Q1 is connected to non-inverting pin 3 of IC1.
Inverting pin 2 of IC1 is connected to voltage-divider preset R4. Using
preset R4 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 (Q2). The high output of IC1 at pin 6 drives
transistor Q2 to energies 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.

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