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Basic knowledge on infrared

What is IR?

Infrared (IR) signals are light waves that are invisible to the human eye. Infrared light is next to
visible light in the electromagnetic spectrum (See Image 1). Infrared light is similar to visible light
– it just has a longer wavelength.

By using invisible infrared light waves, we can control units without interfering with normal human
vision. The light spectrum used for IR remote controls is called “near IR” and its wavelength spans
from 800nm to 2500nm. A typical remote control uses a wavelength of 940nm.

How does it work?

A remote control works by sending a digital signal that tells the receiver what to do. This is done
by turning the IR emitter on and off with a given interval that represents the data to be transmit-
ted (See Image 2) . This type of digital signal is called “unmodulated” IR code.

When sending data by remote control, we must account for other light waves that could interfere
with the transmission of the IR signal. Sunlight, energy saving lamps, fluorescent lamps and other
IR emitting devices (e.g.IRDA) could all potentially interfere with the remote control.
Data sent with unmodulated IR code is prone to instability due to the aforementioned interferences.
To transmit data that is more resistant to external interferences, “modulated” IR code is used (See
in Image 3).

The frequency most commonly used to modulate data is 38 KHz, although this can change from
product to product. There are very few natural sources that share this frequency so it is distin-
guishable when mixed with ambient IR light. Sending “modulated” IR code is the most common way
of overcoming potential interference.
IR remote controls are only capable of one-way communication. There is no way of knowing wheth-
er the device has received the signal or not. However, this should not be a problem as long as an
IR emitter is placed correctly on the device.

 

 

 

 

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