OT? Infrared control and such

[Martin Czech]

:::There are (roughly speaking) infrared equivalents of LED/LDR's at work here, 
:::yes?

Yep, but in contrast to CdS LDRs infrared sending/detecting uses monolithic
silicon. It is the "natural mode" of Si to deal with infrared.
Visible light will need compound semiconductors.


:::Is there a fair amount of natural ambient infrared in our environment as 
:::there is visible light?  

I think a ligth bulb causes 90% heating due to radiation. Only the rest is 
light. Anbd think of the heat of the sun! Also radiation.

:::
:::I gather from using a remote in proximity to an electric guitar and picking 
:::up the electronic noise that the remote is sending pulses to the VCR via 
:::infrared flashes.  While this is probably the logical format of commands 
:::received by the VCR, is this also to cut through any ambient infrared in the 
:::room?

Yes , clever pulse modulation is used to cut away any "dc" infrared signal.
usually the "carrier" has some MHz, the actual telegram is slower,
so that you can hear the current flow. It can be pulses of 1A and more!
This was my very first IC when I started my engineering "carreer":
A tripple diode infrared sender chip. Could deliver up to 2A for the diodes.
And had direction detection by using shutters. This way a pointer could
be run on the TV set, without using a mouse. I think two decades to early...
I made the chip running, but marketing failed...


:::
:::Wireless headphones for quiet TV viewing use infrared also, right?  But I 
:::would imagine it would be analog and thus subject to, I dunno, a hot turkey 
:::sandwich swamping out the signal.

Yep, and the amplifiers have to live from battery charge, which forces
to economise, so bad audio quality... if you want quality, you still
need cables, and you still will step on them, or sit on them and when
you get up you'll hear an awful crashing noise..  due to mechanical
noise conduction in the stressed cable and head set...


:::
:::Getting closer to home, that is, topic, the D-Beam controller uses infrared, 
:::correct?  Any idea how?  (Does infra. reflect?)
:::
:::Generally, I'm trying to get an idea of how these other infrared devices work 
:::so I'd have some informed idea how one would use infrared (much) more simply 
:::in an analog/CV, homebrew vactrol, flashing goofytech theatre of light sort 
:::of way.  It'd be nice to know, for instance, about the nature of 
:::infrared--like whether it's a good idea to put a infrared LDR near something 
:::hot unless you want a high infrared offset that any other source would have 
:::to spike above.  

Well, you need modulation to keep any ovens, the sun , etc. out.
The light source (LED) is a noise device at some 10s of GHz.
Because it is no laser light, the quanta jump arround in a random fashion.
Usually a carrier of some MHz is the applied, neglecting the fact,
that the frequency of the light is "the carrier", but we can't change it,
and it is noise, so we forget about that.

Now, as long as your sensor (LED or transistor) is not overdriven by 
any infrared source (the sun will always do this), you should be able to pick
out the MHz carrier with ease. The frequency is chosen such that cheap
ceramic resonator filters can be used...

You can use any carrier frequency, as long as you'll find a good, affordable
resonator, and as long as the "ringing time" does not distort your message.
Narrow bandwidth means good selectivity and low noise, but more ringing.

m.c