Introduction

Dear reader, in this attempt we are going to make a Short range IR transmitter receiver circuit with relay. In today’s practical electronic market, there are basically two primary types of remote controlled systems available to consumers, IR based remote controlled systems and RF based remote controlled systems. IR stands for Infrared that means the remote face must be pointed directly at the receiver module. RF stands for Radio Frequency that means the remote is multi-directional.

This is a very simple and exciting approach towards the transmitter and receiver world. In which we can operate a motor or a 100 watt bulb or a table fan or whatever you want. Here we will use some simple and easily available components to construct the circuit. Due to the relay provided in the circuit it will support comparatively heavier load which are suitable with the specifications given in the relay. This is suitable only for indoor application. Because the sunlight affects the infrared light emitting diodes.

The fundamental idea behind the project.

In every remote controlled circuit the most common thing is there is a sender (or transmitter ) and a receiver. The receiver should detect the signal of a particular frequency sent by the transmitter and should function accordingly. The basic idea is to send infra red radiation through an IR-LED, and then receive the same  infra red radiation by another IR-LED of the exactly same type.

Light Emitting Diodes (LEDs) exhibit  an electrical property that they develop a negligible amount of potential difference across their terminals when they are exposed to light. Just like  a photo-cell, but the output current is negligible. That means the voltage generated by the LEDs can’t be used to generate a reasonable amount of electrical power from light, It can only be detected. After that the op-amp plays a great role to make the process useful and functional.

Components Required

1. LM 358 (Operational amplifier)
2. Resistors 1 kΩ, 1 kΩ, 4.8 kΩ, 470 Ω
3. Variable Resistor 10 kΩ
4. Relay (5 volt)
5. BC 547 (Transistor)
6. IR LED (1 pair)
7. Red LED
8. Dry cell (1.5 V )
9. Reset switch
10. Vero board

Components Description

LM 358

The op-amp used here is LM358 which is a general purpose op-amp and easily available in market. It is a dual low power operational amplifier. It can operate with a supply voltage from 3V to 32 V.

Relay

Generally relay is defined as an electromagnetic switch. The relay used here is a 5 volt ice cube type.

Resistor

A resistor restricts the flow of current. The resistors used here are carbon film and quarter watt type.

LED (Light Emitting Diode)

It is a transducer which converts electrical energy into light energy.

Transistor

A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit. BC 547 is a general purpose transistor. It is an npn epitaxial silicon transistor. Its maximum collector current (DC) is 100mA.

Working of the circuit.

I have used a 4 volt lead acid rechargeable battery directly as the power source and the 5 volt relay works perfectly with that without any disturbance. But the power source shouldn’t be less than 4 V DC, otherwise the relay will be inactive. You can use three AA size batteries in series to get 4.5 volt supply.  Use a 3*2 vero board to fix the components properly. Here I am giving a 5 volt dc supply circuit using a voltage regulator IC and 9V battery. Use a heat sink for the 7805 voltage regulator IC.

The 7805 voltage regulator IC gives us a constant 5 volt DC power supply from a 9 volt alkaline battery. So , where the rest of the 4 volt goes ? Actually, the rest 4 volts goes nowhere. It is dissipated as heat in the heat sink provided to the voltage regulator IC.

The sender circuit is very funny and still effective. The sender circuit can be made by just connecting an IR-LED with a 1.5 volt dry cell through a reset switch.

The receiver circuit is very simple and effective, there are two 1 kΩ resistors forming a voltage divider which provides 2.5V at the anode of the IR-LED ( this is the sensor in the receiver circuit ). When IR light incidents on the IR-LED the voltage drop increases, the cathode’s voltage of IR-LED may drop as low as 1.4V or more, depending on the light intensity. This voltage drop can be detected using an Op-Amp (operational Amplifier LM358). You  have to adjust the 10 kΩ variable resistor so the voltage at the positive input of the Op-Amp (pin No. 5) would be somewhere near 1.6 Volt. The output will be high when the voltage at the cathode of IR-LED drops under 1.6 volt. So the output will be high when IR light is detected. The output of the Op-Amp is fed to a relay driver circuit to operate comparatively heavier load. The relay driver circuit consists of an npn transistor and a 4.8 KΩ resistor. This is how the receiver works. The working distance is within 1 meter.

How an op-amp works

An operational amplifier is an integrated circuit. Its primary work is to amplify weak electric signals. An operational amplifier consists of two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. The op-amp has 2 input, the +ve input, and the -ve input. If the +ve input’s voltage is higher than the -ve input’s voltage, the output will be high. Even an op-amp can detect a voltage difference of 0.0001 volts.

Application

1. This can be used in a remote controlled car, the range is ofcourse within one meter. Better to operate the remote controlled car inside home.
2. As there is a relay, a comparatively heavier load such as a 100 W bulb or a table fan can also be operated easily.

Watch the video in our YOU TUBE channel for detail information .