Saturday, 9 May 2015

How an Infra-Red Remote control Works

Infrared Remote Controls: Inside
The dominant remote-control technology in home-theater applications is infrared (IR). Infrared light is also known as plain-old "heat." The basic premise at work in an IR remote control is the use of light to carry signals between a remote control and the device it's directing. Infrared light is in the invisible portion of the electromagnetic spectrum.
An IR remote control (the transmitter) sends out pulses of infrared light that represent specific binary codes. These binary codes correspond to commands, such as Power On/Off and Volume Up. The IRreceiver in the TV, stereo or other device decodes the pulses of light into the binary data (ones and zeroes) that the device's microprocessor can understand. The microprocessor then carries out the corresponding command.
To get a better idea of how the process works, let's take a look inside a typical remote control -- the universal remote that came with the author's digital cable box. The basic parts involved in sending an IR signal include:
  • Buttons
  • Integrated circuit
  • Button contacts
  • Light-emitting diode (LED)
To find out more about the parts on a remote-control circuit board, check out Inside a TV Remote Control.
On the component side, the infrared receiver sits on the front of the device where it can easily see the signal coming from the remote control.
You've probably noticed that some remotes only work when you're pointing them directly at the receiver on the controlled device, while others work when you're pointing them in the general vicinity of the receiver. This has to do with the strength of the transmitting LED. A remote with more than one LED and/or a particularly powerful LED produces a stronger, broader signal.
Now let's find out how these parts work together to allow pulses of light to change the channel on a cable box.

Infrared Remote Controls: The Process

Pushing a button on a remote control sets in motion a series of events that causes the controlled device to carry out a command. The process works something like this:
  1. You push the "volume up"button on your remote control, causing it to touch the contactbeneath it and complete the "volume up" circuit on the circuit board. The integrated circuit detects this.
  2. The integrated circuit sends the binary "volume up" command to the LED at the front of the remote.
  3. The LED sends out a series of light pulses that corresponds to the binary "volume up" command.
One example of remote-control codes is the Sony Control-S protocol, which is used for Sony TVs and includes the following 7-bit binary commands.

Radio Remote Controls:

Radio-frequency (RF) remote controls are very common. Garage-door openers, car-alarm fobs and radio-controlled toys have always used radio remotes, and the technology is starting to show up in other applications, too. They're still pretty rare in home-theater devices (with the exception of RF extenders, which we'll discuss on the next page), but you will find RF remotes controlling certain satellite-TV receivers and high-end stereo systems. You'll also find Bluetooth-based remotes that control laptops and smartphones. 
Instead of sending out light signals, an RF remote transmits radio waves that correspond to the binary command for the button you're pushing. A radio receiver on the controlled device receives the signal and decodes it. The problem with RF remotes is the sheer number of radio signals flying through the air at any given time. Cell phones, walkie-talkies, WiFi setups and cordless phones are all transmitting radio signals at varying frequencies. RF remotes address the interference issue by transmitting at specific radio frequencies and by embedding digital address codes in the radio signal. This lets the radio receiver on the intended device know when to respond to the signal and when to ignore it. To learn more about the technology of radio-frequency remotes.
The greatest advantage to radio-frequency remotes is their range: They can transmit up to 100 feet from the receiver (the range for Bluetooth is shorter), and radio signals can go through walls. This benefit is why you'll now find IR/RF remotes for home-theater components. These remotes use RF-to-IR converters to extend the range of an infrared remote.
In the next section, we'll talk about RF extenders and other special remote-control features.

Remote-control Features:

Today's home-theater remotes do a lot more than turn a component on and off and control the volume. Here are just a handful of the features you can find on some of the higher-tech remote controls out there.
Universal capabilities:
Different electronics brands use different command codes. Some IR remotes are preprogrammed with more than one manufacturer's command codes so they can operate multiple devices (sometimes up to 15) of different brands. If your home-theater setup incorporates components from, say, three different manufacturers, you can either use three different remotes to operate your system or use one universal remote. To add functions to a universal remote, you need to know the command codes for the component you want to control. You can look these up online or find them in the manual that came with your remote.
Learning:

A learning remote can receive and store codes transmitted by another remote control; it can then transmit those codes to control the device that understands them. For instance, let's say you have a receiver with its own preprogrammed remote, and you buy a new TV that comes with a universal learning remote. The learning remote can pick up the signals your receiver remote sends out and remember them so it can control your receiver, too. You don't need to input the command codes yourself -- a learning remote picks up and stores the signals another remote sends out. All learning remotes are considered universal remotes because they can control more than one device.
Macro commands:
A macro is a series of commands that you program to occur sequentially at the push of a single button. These macros can be anything you want, such as an "activity command." You can set up a macro that lets you push one button to activate, in order, everything that needs to happen for you to watch a movie or listen to a CD. (Some remotes come with "activity commands" preprogrammed, and others let you download macros from the Internet.)
PC connectivity:
There are remotes that connect to your PC via the USB port so you can install programming software and download command codes and personalized graphic icons (for remotes with LCD screens).
LCD screen:
A remote-control LCD screen may simply display data, or it may be a touchscreen that receives user input.
User interfaces:
Most remotes still utilize the simple button-pushing method, but some have more high-tech manners of inputing commands. You'll find remotes that you operate via an LCD touchscreen, a joystick (for directional commands) and even voice commands.
RF extenders:
Some IR remotes can send out both IR and RF signals. The RF signals aren't meant to control RF devices (in fact, they can't control them). They're meant to extend the operating range of the IR remote control from about 30 feet to about 100 feet (give or take) and allow the signal to penetrate walls and glass cabinet enclosures. The remote automatically transmits both IR and RF signals for every command. When you hook up an RF-to-IR converter (sometimes included with IR/RF remotes, sometimes sold as add-ons) on the receiving end, it receives and converts the signal back into the infrared pulses the device can understand. Now you've got an IR remote that can increase the volume on your home-theater stereo from your bedroom upstairs.
Remote controls are steadily increasing the number of devices and functions they can manage. Some universal remotes intended for home-theater components can learn commands for wirelessly controlled lights, so they will not only start a movie at the push of a button, but they'll also dim the lights for you. Full home-automation systems let you use one remote control to manage lighting, alarm systems and entertainment components by way of a receiver wired directly into your home's electrical wiring. Chances are it won't be long before you have a single remote control to manage every electronic device in your life.

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