Infrared (IR) repeater systems are most commonly used with audio/video systems that distribute video and sound throughout multiple rooms or locations in a home or business. They can often allow full control over each component in the system from every distributed location, assuming each component in the system works with an IR remote. The diagram above shows a common IR repeater system from Buffalo Electronics. It will work with most consumer electronic devices, and will serve as our example.
Infrared is a long wavelength light that is below visibility to the human eye. Light emitting diodes (LEDs) that operate in the IR wavelength are used in remotes as they require very little power, and are able to turn on and off quickly enough to create the digitally-coded messages that remotely-controlled devices respond to. Being light invisible to the human eye, they are not distracting or annoying when in use.
The IR "window" or pick-up on remotely-controlled devices contains a device called a photo diode. These devices are designed to respond to infrared light, recreating the digital code as an electrical pulse, which causes the audio or video component to respond in the desired manner. There are literally hundreds of different code sets for consumer electronic devices.
IR repeater systems are so-named as they simply repeat the IR code produced by an IR remote. The basic system consists of a photo diode unit (often referred to as the "repeater" or IR target), the connecting block which accommodates the power supply and connections, and one or more IR LEDs. They "repeat" the code as seen by the IR target's photo diode for the audio/video devices to be controlled.
So a repeater device must be installed and wired in every location where control over the audio/video system is desired. In the diagram of the Buffalo Electronics system, the IR250 devices on the left are designed to mount into a standard electrical junction box. Three conductors are required in the hook up wire: two for DC power and one to carry the signal. The same type wire used for telephone or alarm system hook up is commonly used in repeater systems, and is generally run in-wall back to the IR100.
When the IR remote is pointed at the IR250 and any button is pressed, the photo diode "sees" the IR emitted by the diode in the remote and creates an electrical pulse equivalent of the IR code. This code is transmitted back to the connecting block, the IR100 in the diagram. The IR100 is powered by a 9VDC wall adaptor, and provides power for the repeaters and emitters. It must be located within a few feet of the audio/video components that you want to remotely control as the emitters generally come with a 6' cord. The IR250 can operate from over 150' of telephone or alarm wire.
Into the right side of the IR100 are connected up to four IR-el emitters. These are simply an IR diode in a small holder, with a 6' cable and 3.5mm DC plug on the end. The diode holder comes with a pressure-sensitive adhesive which allows the LED to be mounted directly over the IR window of each device. When the IR100 receives the pulsed code from any repeater, it causes all of the IR-el diodes to flash the code. Only the device that "recognizes" the code, i.e. TV set, DVD player, etc., will respond. Universal remotes are often used at each repeater location along with that monitor's or TV's remote. Modern universal remotes will work most functions on home audio/video equipment.
Most home audio/video equipment use codes that operate at 40KHz. Some newer components such as digital satellite tuners and digital cable boxes use a higher 56KHz code. Many company's products such as Audioplex will repeat all codes, regardless of the carrier frequency.