ARDUINO CHANNEL SURFER & OTHER DIABOLICAL GADGETS
By Andy Sullivan
A TV remote control uses pulses of infrared (IR) light to communicate. The pulses are
transmitted with an IR LED as a series of bursts separated by off periods. Figure 1
shows a typical transmission. Note that the total signal is almost 90 milliseconds long,
contains approximately 78 bursts, and the durations of bursts and off periods vary.
With an understanding
of the IR codes, a wide
range of devices can be
built delivering new
remote control
capabilities. An example
is a channel surfer that
automatically flips cable
channels similar to the
scan function on radios. Another example is a customized remote that turns on all
entertainment center components with a single button, and manages all component
switching with single button presses (turn on the DVD and select the appropriate input
on the TV). This might help a grandparent who struggles getting three components
configured properly. Other examples include prank devices that change channels, volume,
or turn off a large number of TVs with a single button press such as the TV-B-Gone
advertised on the Internet.
■ FIGURE 1. Typical transmission from an infrared remote control. Many bursts and
off periods of varying durations. Total transmission approximately 90 milliseconds long.
This article will review how to build a channel surfer that will change the channel on over 200 different
TVs. It is a variation on the TV-B-Gone, but has an
advantage around a large number of TVs. If activated
twice, the channel surfer will change the channel again
causing more confusion where the TV-B-Gone will turn a
TV off then back on. The concepts learned in this project
can be used to create a wide range of other IR control
devices.
More on IR Codes
IR signals vary widely and the one shown in Figure 1
is just an example. The signal — or code — is different for
each button on a remote. It is also different for each piece
of equipment (TV, DVD, cable box). Manufacturers use
30 February 2011
different codes, and different models from the same
manufacturer may use different codes. Although there are
a lot of codes, it isn’t a problem as the number can be
trimmed to a manageable level for most projects.
A remaining structural element of an IR code is burst
modulation. Each burst is composed of a series of quickly
modulated flashes. Figure 2 shows a magnified segment
of the same code shown in Figure 1. The full code is
almost 90 milliseconds long. The first narrow burst starting
at eight milliseconds is expanded in Figure 2. The burst
duration is about 0.5 milliseconds and contains 28 flashes.
Each flash has a duration of approximately nine
microseconds with a 50% duty cycle (off time is also 9
microseconds). Frequency of the modulated flashes is
about 55 kHz.
The reason for modulation of the IR bursts is to help
