Difference between revisions of "Infrared notes"

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Infrared is a large enough range to be split into ranges - in a few different ways, even[http://en.wikipedia.org/wiki/Infrared#Different_regions_in_the_infrared].  
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While infrared often refers to near-infrared, it's actually a fairly huge range, split into ranges in a few different ways[http://en.wikipedia.org/wiki/Infrared#Different_regions_in_the_infrared].  
One of them is the near/mid/far split (near/far from the visible spectrum, 380nm..740nm), like:
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The more common seems to be the near/mid/far split {{comment|(near/far from the visible spectrum, 380nm..740nm)}}, like:
  
 
* Near-Infrared
 
* Near-Infrared
 
** Wavelength 740nm to something like 2500nm
 
** Wavelength 740nm to something like 2500nm
** IR LEDs are usually in the 800...1000nm range
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** IR LEDs are usually somwhere the 800...1000nm range
 
** most relevant to optical astronomy{{verify}}
 
** most relevant to optical astronomy{{verify}}
  
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* http://en.wikipedia.org/wiki/Infrared
 
* http://en.wikipedia.org/wiki/Infrared
  
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Revision as of 14:50, 18 February 2013

This is for beginners and very much by a beginner.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.


Some basics and reference: Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect


And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·


Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions


Audio notes: See avnotes

Microcontroller and computer platforms Arduino and AVR notes · ESP series notes · STM32 series notes · · · ·


Less sorted: Ground · device voltage and impedance, audio and otherwise · electricity and humans · power supply considerations · Common terms, useful basics, soldering · PLL · pulse modulation · signal reflection · resource metering · SDR · Project boxes · vacuum tubes · Unsorted stuff

See also Category:Electronics.


This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


While infrared often refers to near-infrared, it's actually a fairly huge range, split into ranges in a few different ways[1]. The more common seems to be the near/mid/far split (near/far from the visible spectrum, 380nm..740nm), like:

  • Near-Infrared
    • Wavelength 740nm to something like 2500nm
    • IR LEDs are usually somwhere the 800...1000nm range
    • most relevant to optical astronomy(verify)
  • Mid-Infrared
    • 2500–25000nm
  • Far-Infrared
    • 25000–1000000nm(verify), getting close to microwave region


See also:


Infrared and cameras

Broadly speaking, there are two main types of IR-related filters:

  • IR-cut filters
    • present in many cameras, because most sensors receive some near-IR.
    • Good ones make sure the contribution is negligible, but they vary in how much they cut. Simple/cheap setups may not yet block much in the 740...800nm region, which is why you can use some cameras to see what your IR remotes are doing (LEDs typically in the 840..940nm range).
  • IR-pass, visible-cut filters
    • which often look black
    • Often start passing at 750..850nm


http://dpfwiw.com/ir.htm#ir_filters


For unfiltered and not-so-strictly-filtered cameras, you can get quick-and-dirty IR by adding an IR-pass,-visible-cut filter: The result is that only the fairly near-IR light gets through. This is what a lot of the see-through IR hacks do. May be quite grainy because there's not much energy getting through, so can be quite grainy. A good source of IR can help. Lightbulbs are decent (actually give off about as much IR as visible light), CFLs not so much. Candles are also great IR sources. There are also cosntructions with a lot of IR LEDs.


Of course, if a camera does proper IR cut, adding such an IR-pass,-visible-cut filter will have the net effect of blocking out almost everything, which means you'll see nothing, or very grainy images at best.

In general, you can get better IR sensitivity by also taking out the IR-cut filter. Depending on the camera, this may be a pretty delicate operation, and tends to be fairly permanent.


Hacks: No, it won't be as good as a heat camera (one of those false-color things).

  • In webcams the IR-cut tends to be a glass in the screwable lense.
  • For DSLRs the IR-cut this is typically a layer on top of the sensor


Communication

Two-directional communication is typically half-duplex because a device can easily be blinded or confused by its own signal.


Consumer IR (TV remotes and such)

  • Often uses a continuous pulse, not continuous sending. This helps confusion from environment IR. This also means you can pulse the LEDs with more current without destroying them.
  • Carrier usually 38kHz. More generally it's somewhere in 33..40kHz or 50..60kHz, often 38kHz, 40kHz, or 36kHz
  • In the case of remotes there are hundreds of variant protocols (that is, bit patterns that are specific to brands and devices)
    • Universal remotes usually have a lookup table from brand-and-model to one of hundreds specific code sets that the remote supports
    • and occasionally the ability to learn codes from an example

http://en.wikipedia.org/wiki/Consumer_IR


IrDA

  • Speed: 2.4 kbit/s to 1 Gbit/s (faster speeds primarily at close range)
  • Modulation: baseband, no carrier
  • Has a few different layers

http://en.wikipedia.org/wiki/Infrared_Data_Association