# How do IR LED work?

R

#### Ricky Spartacus

Jan 1, 1970
0
I am trying to find out whats behind an infrared LED output. When the
IR LEDs terminals are hooked to an analog oscilloscope the waveforms
are square. The waveforms does not change in appearance when other
buttons on the remote are push. It seems any buttons produce the same
patterns. Does this mean I need to use another kind of probe or just
means I dont know how remote control works?

A

#### Anthony Fremont

Jan 1, 1970
0
Ricky Spartacus said:
I am trying to find out whats behind an infrared LED output. When the
IR LEDs terminals are hooked to an analog oscilloscope the waveforms
are square. The waveforms does not change in appearance when other
buttons on the remote are push. It seems any buttons produce the same
patterns. Does this mean I need to use another kind of probe or just
means I dont know how remote control works?

You may have the horiz.. sweep set too fast. This would show you the
carrier (30-40khz) which would look like it didn't change. Set the
horiz. sweep to about 1-2mS/div, this should let you see how the carrier
is turned on and off to modulate the data onto it.

michael

B

#### Baphomet

Jan 1, 1970
0
Ricky Spartacus said:
I am trying to find out whats behind an infrared LED output. When the
IR LEDs terminals are hooked to an analog oscilloscope the waveforms
are square. The waveforms does not change in appearance when other
buttons on the remote are push. It seems any buttons produce the same
patterns. Does this mean I need to use another kind of probe or just
means I dont know how remote control works?

http://www.ee.washington.edu/conselec/A95/projects/pierreg/works/works.htm

J

#### Jim Large

Jan 1, 1970
0
Anthony said:
I am trying to [decode the output of an IR remote]. When the
IR LEDs terminals are hooked to an analog oscilloscope the
waveforms are square. The waveforms does not change in
appearance when other buttons on the remote are push.[...]

You may have the horiz.. sweep set too fast. This would
how you the carrier (30-40khz) which would look like it
didn't change.

It's been many years since I did the same experiment, but I
seem to recall that the remote I was looking at way back when
would send a very short code burst to identify the key,
followed by a continuous waveform that seemed to say, "and
he's still holding it down." The continuous waveform was the
same for most keys, except one or two (like maybe the power
key) that sent the code pattern over and over.

-- Jim L.

A

#### Anthony Fremont

Jan 1, 1970
0
Jim said:
Anthony Fremont wrote:

It's been many years since I did the same experiment, but I
seem to recall that the remote I was looking at way back when
would send a very short code burst to identify the key,
followed by a continuous waveform that seemed to say, "and
he's still holding it down." The continuous waveform was the
same for most keys, except one or two (like maybe the power
key) that sent the code pattern over and over.

Could very well be, IIRC some do work that way. Most remotes fall into
one of two categories: RC5 and RECS-80. One is kind of a PWM system
where 0's are shorter than 1's. Others use a manchester scheme that's
real easy to send, but a pain to decode in software. Sony uses a fairly
simple PWM type protocol.

michael

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