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The Infrared Remote, A Tool For the Lazy

by Rick Prescott

Compiled by Rick Prescott

TV remotes have changed somewhat since they were first invented. Original remotes used the ultrasonic sound produced by a tuning fork that was struck by a hammer when the user depressed a button. The TV was equipped with a microphone to pick up the high frequency sounds. As you can imagine, these early remotes were not exactly loaded with features. On/Off and maybe a channel incrementing feature was about all the control that was offered. Today most TV remotes use infrared light to communicate. Instead of two features, we can enjoy hundreds. But, what if you want to control more than just your TV or stereo with your remote? This resource page should provide you with enough information to get started.

A remote does not do you much good unless you have a way of receiving and interrupting its signals. Although it is possible to build your own receiver unit, it is a lot more practical to purchase one of the hundreds of receiver modules commercially available. These devices are commonly available because of their extensive use in TVs, VCRs, and other popular electronics. A receiver module contains an infrared light detector as well as various electronics to clean up, amplify, and demodulate the signal from a remote control. The remote produces a repeating pattern of on/off pulses of light when a button is pressed. These flashes are modulated from around 38 to 40 kHz. This is to reduce the interference of other light sources present. The receiver eliminates the modulation and provides on/off flashing voltage patterns. These patterns can then be read by other electronics or some form of computer.

The following is a more in-depth explanation of how infrared remote work:

All Infra Red (IR) remote controls use some kind of IR signal. The remotes transmit pulses of IR light to send the signal to the receiver. These IR LEDs transmit light in the frequency range of 30 to 40 kHz. These high frequencies were chosen so that other light sources would not interfere with the receivers ability to correctly receive the transmitted signals. These signals are transmitted by the IR LED in some type of binary code. It turns out that for most consumer electronics this coding is the same. The binary signal varies in length for both time and bit length. There are really only three different ways that manufacturers choose to code these signals. This coding is usually based on varying the length of pulses, varying the length of spaces between pulses, or altering the order between spaces or pulses.

1) Pulse-Width-Coded Signals vary the length of pulses to code the information. In this case, if the pulse width is short (approximately 550 µs) it corresponds to a logical zero or low. If the pulse width is long (approximately 2200 µs), it corresponds to a logical one or high.

2) Space-Coded Signals vary the length of the spaces between pulses to code the information. In this case if the space width is short (approximately 550 µs) it corresponds to a logical zero or low. If the space width is long (approximately 1650 µs), it corresponds to a logical one or high.

3)Shift-Coded Signals vary the order of pulse space to code the information. In this case, if the space width is short (approximately 550 µs) and the pulse width is long (approximately 1100 µs), the signal corresponds to a logical one or high. If the space is long and the pulse is short, the signal corresponds to a logical zero or low.

This coding holds information such as the address to the machine that is using the remote and the command that the machine must follow. The address is important because without it the signal would be processed by another IR receiver in the area.

When a button on a remote is pushed it sends a string of signals. The first piece of information in the string is called the Header. The Header usually contains a burst of highs that alerts all the IR receivers in the area to the string of data being sent. Following the burst of highs is the address to the specific machine to receive the next piece of data, the command. As long as the button is held down (depressed), the command will continue to repeat. When the button is released, a string of code called the stop is transmitted. As you may have guessed, the stop tells the machine to stop its executing of the command.

Here is more information on decoding:

Decoding IR Remote Controls—There are at least two international standards used by remote controls to encode the commands, the RC5 and RECS 80 code.
RC5 (a widely used protocol)
Control-S (used by Sony for both wired and IR control)
Sharp television
RCA television

Datafiles for:
Kenwood RC-6010 Remote
Mitsubishi VCR/audio/TV
Sony CD Player RM-D505 Remote
Sony CD Player RM-DX100 Remote

If you are looking for a little more information on the remote that you are trying to use to control your devices and device codes, the following page might be helpful—U-OFA-URC: The Unofficial One-For-All Universal Remote Control Pages

Information about each controllable device preprogrammed into the remote and referenced by a three-digit "Device Code". The owner's manual for each remote has a big table of brand names and the associated device code(s) for Televisions, VCR's, cable boxes, and other controllable equipment. You associate a Device Code with each of the device keys on your remote to tell the remote what equipment you have.

Links from the Official FAQ:
Device Codes—those vital tables of two, three or four-digit numbers in that owner's manual, which you put somewhere safe and now can't find.
Setup Instructions—the other vital part of that owner's manual which you put somewhere safe and now can't find. These tell you how to use the Device Codes.
How to send an Upgradable model back to the factory for additional device codes
Tells you what kinds of device codes work on your remote—some low-end models can only do TV and VCR.
Store chains which carry OFA remotes
Basic problem-solving
A list of model no longer made
This site has more Advanced Codes tables
Universal Remote Control, Inc.—another maker of universal remote controls.

Examples and Projects:

BasicX application note: Interfacing Infrared Sensors

"This application note describes the hardware and software required to interface a Sharp infrared sensor to a BasicX BX-24 system.
The Sharp GP1U52X infrared detector (Radio Shack #276-137) is designed to receive modulated IR data signals from most handheld IR remotes. The sensor demodulates a 40 kHz IR signal and converts it into a serial data stream. By connecting the device to the input capture pin of a BX-24 system (pin 12), this steam of data can be captured and saved as an array of integers. The array can then be transformed into unique command codes."

As shown in the figure above, interfacing the Sharp IR detector to the BasicX requires only one 5-kW resistor and three wires. You can solder the resistor to the back of the IR unit and eliminate the need for a separate circuit board. The device also requires a stable 5-V supply for reliable operation. For a regulated 5-V supply, you can use pin 21 on the BX-24. Pin 23 can be used as ground.

Parallax basic stamp application note: Infrared Communication

A Serial Infrared Remote Controller—This is a simple, inexpensive device that can be connected to any serial port to control most components that have infrared remote controls. Source code for the program that reads the data sent by the IR remote receiver and converts it to the function code that identifies the button pressed.

How to built a universal infrared remote control system for a Sony minidisk Walkman—He has created (and tested) one for his MZ-R50 walkman and thinks it will also work fine with other Sony models, such as MZ-R2, MZ-R3, MZ-R30, MZ-R35, MZ-R37, MZ-R55, MZ-R70, MZ-R90, and MZ-R91 (also MD players are supported).

The following page will show you how to build your own infrared receiver for the serial port. Please note that the serial port driver in the LIRC package only supports 8250 compatible UARTs (this includes the most common 16450 and 16550A types). That means that it won't work with exotic multi-port cards that need a special driver.

Serial Port Transmitters

Universal Infrared Receiver by Ties Bos

Looking Inside a Remote—If you are like most Americans, you probably pick up a TV remote control at least once or twice a day.

More links from ePanorama

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