The term “infrared” refers to electromagnetic waves whose wavelength is shorter than that of visible light. But although they are invisible to the naked eye, infrared radiation is constantly emitted by objects at room temperature, whatever they are.
These electromagnetic waves (which range from ~0.7µm, the visible range, to ~1µm, the microwaves) are used in many, sometimes very different, fields. Here, we will discuss data transfer, communication
How it works
To emit an infrared signal, we use an infrared LED, (and to receive them, we can use a phototransistor or a photodiode).
To transfer data, binary communication protocols such as SIRCS, invented by Sony, or Phillips’ RC5 (the most widely used) are used.
Infrared coding
Depending on the protocol, the operation varies, but basically, the LED sees a binary code by switching on and off quickly. These variations, or, depending on the protocol, the time between each of its variations, defines how the receiver should interpret the binary message.
Also, as there are many surrounding infrared sources (the sun being the main source), the receiver knows when a message is being sent to it thanks to the frequency of infrared radiation, which is always the same (when the LED is on ON)
Finally, whatever the protocol, the signal (or frame) is always divided into several parts:
- a certain number of start bits are defined for synchronization with the device,
- a certain number for the instruction itself,
- an address code, to know who the message is intended for (DVD player, TV…)
- an end code
Use and Disadvantages
The first use of infrared coming to mind is of course that of remote controls (television, garage door…). This method of communication is preferred over others because it is less prone to interference.
Infrared, although it has a relatively high flow rate (10Mb/s theoretical), has the enormous disadvantage of having a very short range and being very easily stopped by obstacles. It is therefore a technology that is perfectly suited to communication between close devices, and having a “direct aim” at each other, such as a television and its remote control.
With infrared transmissions, it is necessary to be physically close to the transmitting device to divert data.
No need to choose passwords that are ultra-secure and difficult to remember. A simple agreement of both the issuer and the recipient.
There are four modes of infrared networks:
- Line-of-sight networks (devices are close enough to each other to avoid visibility problems)
- Diffusion infrared networks (signals are reflected by walls over 30 meters, but the flow rate is very low)
- Reflective networks (signals are received by a single point that acts as a router and redirects them to the recipient)
- Broadband optical link networks (with a higher throughput than others, they allow the transmission of multimedia files.)
IrDA
The Infrared Data Association is a special infrared communication protocol based on the OSI model. It uses its own components and protocol. Although it was used extensively in the 1990s and early 2000s, it was mainly forgotten without Bluetooth knowledge. It allowed communication between PCs, phones and PDAs…
However, it has been making a comeback in recent years, integrated into smartphones, in order to transform them into universal remote control, to control televisions, cameras… using applications.
