[TriEmbed] IR remote signals

[John Wettroth]

The LTR-301 is just a photo transistor.  As was said, with a 1k pullup, it
will work about a foot but will not be what you expect from a remote.  It
will also have soft edges due to the open collector output and capacitance
of the transistor.  You could improve it by following with a comparator with
a bit of hysterisis but you still won't get what you probably expect.
 
IR Remotes are transmitted with manchester encoding (like PWM) on a low
freqency carrier- usually 32Khz or 40 Khz- Sony is 40 Khz.  This carrier
allows the reciever to be narrow band and allow it to have a lot of gain
without turning into a noisy mess.  What you want is a IR Reciever module,
these generally look like a photo transistor but actually have an amplifier,
bandpass filter and data slicer in them which give a logic out- also with a
pull up.  Below is a link that is pretty good.  IR reciever modules are not
hard to find.  I have some around here if you're in a time bind and need one
today.
 
Here's the link-
https://faculty-web.msoe.edu/johnsontimoj/Common/FILES/sony_sirc_protocol.pd
f
 
 

Regards,
John M. Wettroth
(984) 329-5420 (home)
(919) 349-9875 (cell) 

 

  _____  

From: TriEmbed [mailto:triembed-bounces at triembed.org] On Behalf Of Shane
Trent via TriEmbed
Sent: Tuesday, October 20, 2020 10:03 PM
To: Paul MacDougal
Cc: TriEmbed Discussion
Subject: Re: [TriEmbed] IR remote signals


You need more pull-up. Use an external 1k pull-up and you should see the
square waves.

On Tue, Oct 20, 2020 at 8:37 PM The MacDougals via TriEmbed
<triembed at triembed.org> wrote:


See the attached scope shot.

This is one mark from a SONY remote captured by an LTR-301 IR detector.

https://www.sparkfun.com/datasheets/Components/LTR-301.pdf

I have this device attached to an Arduino Uno and am using INPUT_PULLUP
(internal pullup on the pin).

 

I think that the wiggle on the scope between the cursors is the 40kHz
modulation of the signal.

The cursors cover 10 wiggles and the scope reports 4.04 kHz.

My question is why is this wiggle of such small magnitude? I was expecting
to see full voltage swing.

Is it just this particular IR detector?  Is there something in the datasheet
that would indicate this?

 

 

---> Paul

 

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