Perusing a universal remote
Prying Eyes: Universal remote controls tackle the difficult problem of mimicking the myriad command signals that electronic-device manufacturers employ.
By Robert Cravotta, Technical Editor -- EDN, October 25, 2007
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During the 1950s, Zenith Radio Corp introduced the first remote control for television. The Lazy Bones device used wires between the remote and the TV. Wireless remote controls appeared shortly thereafter, and the industry has been evolving and improving them ever since. As home-entertainment systems started to include more types of devices, such as DVD players, cable or satellite set-top boxes, and audio systems, the demand has grown to combine the separate remote controls for each of these devices into a single device.
An industrywide remote-control standard would be ideal, but such a solution seems unlikely in the immediate future. The URC (universal remote control) is an approach to help reduce the frustration of using multiple and incompatible remotes to control home-entertainment systems. This Philips Prestige SRU8015 includes many of the components that you typically find in URCs.
A URC employs one or two key capabilities to support the myriad devices available today. The ability to directly learn and mimic the signals of a device is one of these capabilities. For this approach, the user must manually control and coordinate between the device, to mimic, and the URC, to "teach," the URC each of the device’s command signals. This process can be time-consuming and leaves plenty of room for operator error.
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Remote-control manufacturers can use an embedded-device infrared-command database to teach their URCs to mimic multiple device controllers, thereby relieving users of that task. Companies such as Zilog and Universal Electronics have built extensive proprietary infrared-command databases that include the signal and timing codes to control electronic devices.
An infrared-command database must encompass signals from all the popular brands of consumer-electronic appliances. Compiling the data from OEM remote controls is more work, but it results in a smaller and more reliable database than capturing the signals from other URCs because it avoids duplicate entries and enables a smaller ROM footprint for the database.
A URC must be simple to program and easy to use. Some URCs include the learning function to complement and augment the embedded infrared-command database so that the URC can control devices that the database does not include. Another key consideration for ease of use is ergonomics. Most people use their thumbs to press buttons on a remote control, and the buttons they most frequently press are the channel-up and -down buttons. So, designers of effective remote-control layout locate these buttons in locations that users can easily access with their thumbs. The size and backlighting of the buttons are also important, especially for older users.
Most URCs today employ direct-code entry. To program in another appliance requires looking up the code in the manual and then entering it while the remote is in programming mode. Unfortunately, most manuals provide a long list of codes for each brand. The user often must go through a hit-or-miss process to identify the right code for the appliance. An alternative approach—the brand-code search—allows the user to enter the brand, and the remote control automatically searches for the code. The RCA RCR815 remote control in these images uses this approach.
Another advanced feature, which the Philips Prestige SRU8015 includes, has a built-in interactive programming guide. The remote control allows users to scroll up or down until they find the right brand. They then enter the brand, and the remote handles programming.
A learning function is important for complementing any missing key signal in the database. Most URC databases omit unpopular key functions. For example the MTS/SAP (multichannel-television-sound/second-audio-program) function switches to audio-language channels, and the CC (closed-captioning) function displays captions at the bottom of the screen. The ideal URC should also contain some macro functions to enhance ease of use. For example the RCR815 includes a hot-wire function that sends a power-off signal to all of the equipment when a user presses the power-on/off button twice. The user does not need to switch to and command each individual appliance to the power-off state. A second macro allows the user to program buttons to automatically dial up certain channels. For example, a macro key can transmit the key signal 202, which would normally require three key presses, in one key press.
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Another key consideration is battery life, so designers build remote controls with low standby current in mind. They can also include an EEPROM or a flash nonvolatile memory to ensure that the user need not reprogram the remote control whenever batteries require replacement.
The microcontroller provides the opportunity not only for more complex functions, but also increased reliability and performance. It can also reduce cost by integrating and eliminating the need for external components, such as a filter, automatic gain control, and an amplifier.
Special thanks to Dan Mui of Zilog for sharing his invaluable insights and knowledge about designing remote controls.
