Descriptio
Parts:
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:
Circuit Diagram:
Parts:
- R1 = 470R
- R2 = 100K
- R3 = 3.3K
- R4 = 10K
- D1 = 1N4007
- D2 = IR LED
- Q1 = L14F1
- RL = 5Vdc Relay
- IC = CA3140
- Q2 = BC548
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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