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[DPRG] Spectral Content

Subject: [DPRG] Spectral Content
From: Michael C. Menefee mikem at mnetwork.org
Date: Sun Jul 27 20:11:53 CDT 2008

Most remotes use a laser diode at 808 or 850.  While this is in an
atmospheric pass band, the detector sensitivity comes from the
modulation, not the wavelength.  Radio Shack used to sell remote control
receiver modules.  Not sure if they still do.

A couple more data points:
- any Si-based detector is going to start falling off in sensitivity
around 900nm, +/- 100nm or so depending on how they doped it.

- Until you get out to around 5000 nm or so any IR you see will be due
to natural or artificial light.  Thermal IR is well below what you're
doing with anything in the 700 to 2000 nm range.

-----Original Message-----
From: Ed Paradis [mailto:legomaniac at gmail.com] 
Sent: Sunday, July 27, 2008 5:50 PM
To: Kenneth Maxon
Cc: dprglist at dprg.org
Subject: [DPRG] Spectral Content

That is a great graph. It looks like there is a big gap around 900nm
and another around 1100-1200nm.  I wonder if the 'IR' that most
remotes use is around that range.  It would be wise, as at that point
your signal to noise ratio would be much better.

Ed

On Sun, Jul 27, 2008 at 3:23 PM, Kenneth Maxon <kmaxon at qwest.net> wrote:
>
>
> Good observation.  In the IR range there is still plenty of spectral
> content, although from a energy delivered as natural light source it
is
> beginning to fall off.  On the other hand, in the UV spectrum the
earth's
> atmosphere is quite good at blocking a large percentage of the energy
coming
> through.
>
> http://squ1.org/files/wiki/solar/spectral-content.gif
>
> -Kenneth
>
>
>
> -----Original Message-----
> From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]On
> Behalf Of John Swindle
> Sent: Sunday, July 27, 2008 1:43 PM
> To: dprglist at dprg.org
> Subject: RE: [DPRG]Wall-E -> 1GHZ computers laser rangefinding
>
>
> Folks:
>
> I disagree with one of the comments about using IR instead of
> visible light, supposedly because there is too much visible light
> noise in the environment. A similar reasoning error is made when
> thinking about using 40KHz for sonar, thinking that there's less
> sound noise around that frequency. Just because we can't hear or
> see something says nothing about how much noise there is at those
> frequencies. Indeed, there's lots of IR noise. Everything is
> somewhat hot. And for sonar, the harmonics of our machines and
> our squeaky sneakers are well above our range of hearing. The key
> to rejecting noise is the modulation.
>
> Back to my passive sonar stuff now. (I'm using audible sound so
> that I can debug it with my ears instead of always depending on
> the microphones and calculations.)
>
> John Swindle
>
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