Principles of Infrared Remote Control

Principles of infrared communication & Infrared Remote Control

Infrared is an invisible light to the naked eye, with a wavelength of approximately 950nm. Infrared light however can be detected with one of the modern digital cameras that have night vision functionality.

Digital Infrared messages are create by transmitting short and long pulses of infrared light. The code is similar to the principals of Morse code using long and short pulses. A long pulse of 1.2ms is represented a digital 1 and a short pulse of 0.6ms is represented as a logic 0. There is a 0.6ms pause between each pulse.

To gain some immunity from ambient light sources (e.g Sunlight), the IR sensors ‘trigger’ only when a 32KHz-40KHz modulated IR signal is sent. The sensors used in the IR-CF are PNA4620M-ND from Panasonic (or similar component) that has a centre frequency of around 38KHz.

This means that , the sensors will only recognise a 1 or 0 pulse, once sending bursts of Infrared light at a frequency of 32Khz – 40Khz. If we use the formulae [seconds=1/frequency], we see that the pulse width is 31,25– 25.0 uS (microseconds). Remember that uS is one millionth of a second or thousandth of a millisecond! For a Peak sensitivity of 38Khz,that is 26.32 uS per pulse. This calculates to 22.8 (say 23) IR pulses for a '0' pulse (0.6ms =600us) and 45.6 (say 46) IR pulses for a '1' (1200us) pulse.

The sensors used in the IRCF360^TM and IRCFL^TM are PNA4620M-ND from Panasonic (or similar component), which has a centre frequency of 38Khz. The sensitivity of these sensors is dependent on the modulated frequency. The frequency bandwidths are very narrow. A few Khz too low or too high reduces the sensitivity dramatically, as depicted in the graph below. This can be used in a postive way by programming a variable modulation frequency to test various distances of proximity 'zones'. This feature is already included as one of the programmable paramteres in some of the commands.

Sending Sony 12-BIT SIRC standard IR packages

The SIRC infrared signal is made up of a 12-bit packet, which is split into a 7-byte button code and a 5-byte device code. The button code represents the actual button pressed on the remote control. There is a 2.4ms ‘start bit’ between each packet, which is used to synchronize the sensors.

The device code determines which remote control device is being address; such as video, television, CD, Amplifier, SAT, etc (see ref: below).

Infrared Remote Control within the IR Control Freak Modules

IRCF360^TM and IRCFL are equipped with an on-board infrared remote controlled receiver and transmitter, so that it is possible to control robots or other electronic projects using a standard TV remote control that can transmit Sony SIRC (12-bit version). The protocol used with IR Control Freak is the Sony format known as SIRC.

A remote control feature enables inter-robot communication and Robot Gaming such as tag, zapping, Robot team communication, etc.

Buy using coded IR messages; you can transmit signals to other robots. For example:

- It is possible to determine whether your robot opponent is a friend or foe
- You could also configure a unique ID for each robot and robot team, allowing your robot to communicate between team members and sending a 'tag' or ‘zap’ code to the other opponent team. For example, ten ‘zaps’ to sent and acknowldeged by component robot could mean, "your it!"
- Simple communication to other swarm robots signalling that food has been located

REF: