How do IR LED work?

R

Ricky Spartacus

Guest
I am trying to find out what`s behind an infrared LED output. When the
IR LED`s 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 don`t know how remote control works?
 
"Ricky Spartacus" <RickySpartan@mailandnews.com> wrote in message
news:d1e1d73f.0310150339.61d1796f@posting.google.com...
I am trying to find out what`s behind an infrared LED output. When the
IR LED`s 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 don`t know how remote control works?
Click to expand...
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
 
"Ricky Spartacus" <RickySpartan@mailandnews.com> wrote in message
news:d1e1d73f.0310150339.61d1796f@posting.google.com...
I am trying to find out what`s behind an infrared LED output. When the
IR LED`s 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 don`t know how remote control works?
Click to expand...
http://www.ee.washington.edu/conselec/A95/projects/pierreg/works/works.htm
 
Anthony Fremont wrote:

"Ricky Spartacus" <RickySpartan@mailandnews.com> wrote in message
news:d1e1d73f.0310150339.61d1796f@posting.google.com...

I am trying to [decode the output of an IR remote]. When the
IR LED`s 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.
Click to expand...
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.
 
Jim Large wrote:
Anthony Fremont wrote:

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.
Click to expand...
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
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top