After using the wash basin mirror lamp, it is easy to forget to turn off the light after being in a public space, an auditorium, or even in your own home. When you stand in front of the wash basin mirror lamp, the circuit shown below will turn it on automatically, and it will turn off again when you move away from it, helping you save money on your electric bill. The individual standing in front of the mirror will cause the modulated 38kHz square wave pulses emitted by the infrared LEDs to be reflected back to the sensor that is located behind the mirror. When the receiver sensor detects infrared rays, it energizes the relay for a predetermined delay period, which in turn causes the washbasin lamp to turn on for the duration of that delay. The wiring diagram for the automatic washbasin lamp controller may be found in Figure 1. It is made up of two parts, namely, a receiver and a transmitter for infrared radiation. While IC1 and IC2 serve as the primary building blocks for the transmitter part, IC3 serves as the primary building block for the receiver section. In the circuit for the transmitter, IC1 performs the role of an astable multivibrator and generates pulsed output at a frequency of 5 Hz. The pulsed output at 5 Hz allows IC2 to function by way of transistor T1. In addition to this, IC2 is set up to function as an astable multivibrator that generates a square wave at 38 kHz. The changeable 10-kilo- ohm potmeter can be used to alter the output frequency of IC2, which can be done at any time. Through driver transistor T2, the output of IC2 is sent to two IR LEDs.

The TSOP1738 infrared (IR) sensor, 1N4148 switching diode (D1), IC555 timer (IC3), BC548 relay-driver transistor (T3), and other components make up the receiver circuit. When an IR radiation is detected, the sensor will activate IC3, which is configured to operate as a monostable multivibrator and has a period of around 24 seconds. Simply by adjusting the numbers in R11 and C7, the time period can be altered to take on any value that is required. It is possible to link the output of IC3 to the relay-driver transistor T3. When the sensor receives modulated 38kHz IR pulses from the IR transmitter, conductivity is established in transistor T3 for a period of 24 seconds. This causes relay RL1 to become energized, and the normally-open (N/O) contact of relay RL1 becomes connected to the mains AC terminal of the mirror light, which then turns on the wash basin mirror lamp for a period of 24 seconds. As a result, the lamp in the wash bowl mirror turns on automatically whenever there is someone standing in front of it. In any other case, it will remain off. The entire circuit is powered by a regulated 9-volt supply of electricity. Put it together on any kind of general-purpose PCB, encase it in an appropriate cabinet, and then mount it behind the mirror of the wash basin.