Communication Using Infrared Technology

Infrared Communication

Infrared band of the electromagnet corresponds to 430THz to 300GHz and a wavelength of 980nm. The propagation of light waves in this band can be used for a communication system (for transmission and reception) of data. This communication can be between two portable devices or between a portable device and a fixed device.

There are two types of Infrared communication

• Point to Point: It requires a line of sight between the transmitter and a receiver. In other words the transmitter and the receiver should be pointed to each other and there shouldn’t be any obstacles between them. Example is the remote control communication.
• Diffuse Point: It doesn’t require any line of sight and the link between the transmitter and the receiver is maintained by reflecting or bouncing of the transmitted signal by surfaces like ceilings, roof, etc. Example is the wireless LAN communication system

Advantages of IR communication:

• Security: Infrared communication has high directionality and can identify the source as different sources emit radiation of different frequencies and thus the risk of information being diffused is eliminated.
• Safety: Infrared radiation is not harmful to human beings. Hence infrared communication can be used at any place.
• High Speed data Communication: The data rate of Infrared communication is about 1Gbps and can be used for sending information like video signal.

IR Communication basics:

IR transmission

The transmitter of an IR LED inside its circuit, which emits infrared light for every electric pulse given to it. This pulse is generated as a button on the remote is pressed, thus completing the circuit, providing bias to the LED.

The LED on being biased emits light of the wavelength of 940nm as a series of pulses, corresponding to the button pressed. However since along with the IR LED many other sources of infrared light such as us human beings, light bulbs, sun, etc, the transmitted information can be interfered. A solution to this problem is by modulation. The transmitted signal is modulated using a carrier frequency of 38 KHz (or any other frequency between 36 to 46 KHz). The IR LED is made to oscillate at this frequency for the time duration of the pulse. The information or the light signals are pulse width modulated and are contained in the 38 KHz frequency.

IR Reception

The receiver consists of a photodetector which develops an output electrical signal as light is incident on it. The output of the detector is filtered using a narrow band filter that discards all the frequencies below or above the carrier frequency (38 KHz in this case). The filtered output is then given to the suitable device like a Microcontroller or a Microprocessor which controls devices like a PC or a Robot. The output from the filters can also be connected to the Oscilloscope to read the pulses.

Parts of IR communication system:

IR Transmittor- IR Sensor

The sensors could be utilized as a part of measuring the radiation temperature without any contact. For different radiation temperature ranges various filters are available. An infrared (IR) sensor is an electronic device that radiates or locates infrared radiation to sense some part of its surroundings. They are undetectable to human eyes.

An infrared sensor could be considered a Polaroid that briefly recalls how an area’s infrared radiation shows up. It is very regular for an infrared sensor to be coordinated into movement indicators like those utilized as a feature of private or business security systems. An IR sensor is shown in figure; basically it has two terminals positive and negative. These sensors are undetectable to human eyes. They can measure the heat of an object and also identify movement. The region wavelength roughly from 0.75µm to 1000 µm is the IR region. The wavelength region of 0.75µm to 3 µm is called close infrared, the region from 3 µm to 6 µm is called mid infrared and the region higher than 6 µm is called far infrared. IR sensors emits at a frequency of 38 KHz.

Features of IR Sensor:

• Input voltage: 5VDC
• Sensing Range: 5cm
• Output signal: analog voltage
• Emitting element: Infrared LED

Example interfacing circuit of IR diode and photodiode

IR sensors mostly used in radiation thermometer, gas analyzers, industrial applications, IR imaging devices, tracking, and human body detection, communication and health hazards

Here is a brief description of IR & Photo diode sensing switch:

An IR diode is connected through a resistance to the dc supply. A photo diode is connected in reverse biased condition through a potential divider of a 10k variable resistance and 1k in series to the base of the transistor. While the IR rays fall on the reverse biased photo diode it conducts that causes a voltage at the base of the transistor.

The transistor then works like a switch while the collector goes to ground. Once the IR rays are obstructed the driving voltage is not available to the transistor thus its collector goes high. This low to high logic can be used for the microcontroller input for any action as per the program.

IR Receiver/TSOP Sensor – Features & Specifications

TSOP is the standard IR remote control receiver series, supporting all major transmission codes. This is capable of receiving infrared radiation modulated at 38 kHz. IR sensors we have seen up to now working just for little short distance up to 6 cm. TSOP is sensitive to a specific frequency so its range is better contrast with ordinary photo diode. We can alter it up to 15 cm.

TSOP acts like as a receiver. It has three pins GND, Vs and OUT. GND is connected to common ground, Vs is connected to +5volts and OUT is connected to output pin. TSOP sensor has an inbuilt control circuit for amplifying the coded pulses from the IR transmitter. These are commonly used in TV remote receivers. As I said above TSOP sensors sense only a particular frequency.

Features:

• The preamplifier and photo detector both are in single package
• Internal filter for PCM frequency
• Improved shielding against electrical field disturbance
• TTL and CMOS compatibility
• Output active low
• Low power consumption
• High immunity against ambient light
• Continuous data transmission possible

Specifications:

• Supply Voltage is –0.3-6.0 V
• Supply Current is 5 mA
• Output Voltage is –0.3-6.0 V
• Output Current is 5 mA
• Storage Temperature Range is –25-+85 °C
• Operating Temperature Range is –25-+85°C

The testing of TSOP is very simple. These are commonly used in TV remote receivers. TSOP consists of a PIN diode and pre-amplifier internally. Connect TSOP sensor as shown in circuit. A LED is connected through a resistance from the supply to output.

And then when we press the button of T.V. Remote control in front of the TSOP sensor, if LED starts blinking then our TSOP sensor and its connection is correct. The point when the output of TSOP is low i.e. at the time it appropriates IR signal from a source, with a centre frequency of 38 kHz, its output goes low.

TSOP sensor is used in our daily use TV, VCD, music system’s remote control. Where IR rays are transmitted by pushing a button on remote which are received by TSOP receiver inside the equipment.

Photo Credit:

• IR communication principle by sbprojects