I have been dealing with IR for about 10 years. My initial claim to fame was a paper I wrote that described Pronto HEX for the world at large. It has been downlaoded over 75,000 times and translated to at least 5 languages. Probably helped establish Pronto HEX as a default interchange format since it was precisely documented. It is on this site somewhere. Seek and ye shall find.
I use a lot of Xantech gear because years ago it was the only game in town, but today take your pick.
IR as a mechanism is a flashing light beyond the range of frequencies that make up the visible spectrum. That is, the frquency of the light (its color) can not be seen by the human eye. The light is flashing (at a frequency called the carrier frequency) so that electronically it may be easily detected and seen in the presence of other "Light" noise. That frequency is decided by the manufacturer. Most remotes run at a frequency of about 40khz, but some (some new Pioneer, Bang and Olafsun to name a few) are much higher. The IR receiver is tuned to only "respond" to light in the IR spectrum flashing at the given carrier frequency. The frequency tolerances are pretty wide (generally about +/- 10%).
The information is "Carried" by the flashing light by encoding the binary patterns as sequences of flashing light on and flashing light off. Some times it is the duration of the on time that has the information, sometimes it is the off time, some times it is a combination, and lastly each manufacturer can do it any way they want using different timings (600 microsec on, 600 microsec off=0; 1200 microsec on, 600 microse off =1 or any thing they want)
Fortunately for the world at large mass produced chips are cheap small chip runs are very very expensive, so as something gets popular a single chip that does all of the work, decoding the patterns of flashing light into binary numbers. The rule in electronics is for everyone to only buy things made from the same chips, they will get cheaper and cheaper.
There are about 4 variants (chips) now used by 90% of the manufaturers of componets which have IR receivers. Of the 4 one is very popular and referred to as the NEC protocol or the Asian protocol. Obviously Sony does it its way and is one of the 4, Sharp or Samsung also might, Philips does. Why - because they are chip makers and they can. People who can not make chips and build things like receivers, scalers, DVD players use a chip made by a chip manufacturer and most often it is NEC.
An IR blaster is merely an emitter that puts out a lot of invisible light. It may be several emitters bundled into a single package and generally wired in series, ergo you can make your own.
An IR sender such as a Pronto Extender puts out its signal on two wires, signal and return. Most IR emitters are built so that a very small amount of current (10-20 milliamps) drives the emitter at sufficient brightness (energy output). The emitter is almost always a Light Emitting Diode (LED).
Hooking one up backwards will not hurt it or the IR sender, it just will not work. Most IR senders can drive an emitter over several hundred feet of 22-24 gauge wire. I often just use a spare pair (Brown/Brown-white or Blue/Blue-white) of an existing CAT 5 cable to run the IR signal around the house. Cat 5 cables are classically in the 100 meter (300 feet) range between repeaters/devices/hubs/switches. Xantech claims that the output (IR Sender port) of one of its amplified hubs will drive several thousand feet of wire. A typical Xantech amplified huib has 10 IR ports with the ability to set each port to Hi or Lo Power.
Most IR senders can drive several emitters wired in series. In fact a very common emitter being sold is really two emitters (LED's) wired in series on a single cable terminating in a mono 3.5mm (1/8") plug. I have done several hundred feet of 24 gauge wire driving 4 emitters in series from a Global Cache IR sender. Most IR senders limit the current they can send out (internal series resistor) so a dead short across the IR sender output port will not hurt it. Too many emitters, not enough invisible brightness; out comes the trusty Dink-Link so I can see what is happening
There are emitters that also emit not only IR but also light in the visible spectrum. These are very handy just to prove that the circuit is working, ie the wiring is correct and the emitter is flashing. Xantech sells them as "Dinky-Links". I keep a couple in my tool box.
A significant issue is having two identical components that take the same IR signals with no ability to change them. Tivo's and Sony devices allow you to use a different code for identical devices. Scientific Atlanta does not. If you have two SCI ATL DVR's (as I do) in the same rack, then you must zone your IR so that they both do not see the same signal. That eliminates the use of an IR blaster. After all if one is recording, and the other is channel surfing, you do not want the one recording to change channels.
I will answer IR questions, but if you want me to really help you might have to send me the Pronto hex codes that are giving you a problem. I can not tell you what codes mean what for most esoteric devices. Sony is fairly standardized, Apple is not, NEC format is a protocol for transmission it is not the coding of the information, but given enough samples I can gereally reverse engineer the code formats, that is, deduce possible codes that are not on the remote.
