IR Remote Control Contemplates Graceful Retirement

By: Kjartan Furset, Nordic Semiconductor
( 1 Mar 2008 )

European consumers are spending more of their hard-earned euros on home entertainment equipment than ever before. Digital music players, camcorders, "media centers", large-screen TVs and gaming consoles are flying out the retailers' doors.

Most of these appliances use IR (infrared) wireless communication. It's simple to design-in, robust, cheap to manufacture and yields a controller that can run for months on two to four AAA 1.5V cells. However, IR remote controls were originally designed in the late seventies to replace ultrasonic devices when a greater range of functionality was required and are starting to show their age. For example, IR remotes are inconvenient to use when navigating the complex multi-layered menus typical of today's digital electronics.

Moreover, users have to point the remote directly at the IR receiver on the equipment they wish to control which means they need a clear path unobstructed by people, furniture and walls. And IR is typically a uni-directional communications technology (bi-directional communication is possible, but it's expensive and prone to interference from other light sources). This was fine for consumers in the 80's looking to do little more than change TV channels or increase volume, but in 2007 consumers demand a user interface on their remote offering intuitive instructions and information about the media they're listening to or watching.

Fortunately, a new generation of RF (radio frequency) remotes promises to finally match the convenience of IR—design simplicity, low cost and long battery life—while providing consumers with wireless connectivity that can support the more-advanced menu-based browse facilities now common to home entertainment devices.

Better yet, the silicon vendors are making great strides to simplify the traditionally tricky RF design process by offering industry-proven transceivers plus reference designs, customized protocols and RF expertise to assist inexperienced designers.

IR EXPOSED
IR is electromagnetic (EM) radiation of wavelengths longer than visible light, but shorter than RF spanning three orders of magnitude between 750nm and 1mm. IrDA, the Infrared Data Association, champions IR in the electronics sector and most offerings adhere to the organisation's standards, aiding interoperability.

IR remote controls use IR LEDs to emit radiation that's focused by a plastic lens into a narrow beam. Data is encoded by modulating the beam to provide immunity from other IR sources such as fluorescent lights. The receiver uses a silicon photodiode to convert the IR radiation to a current for decoding by the receiver's MCU. IR doesn't penetrate walls—although it can be reflected by walls and ceilings—and so generally does not interfere with other devices in adjoining rooms.

A simple IR remote is composed of a keypad to input instructions, a resonator to provide a reliable clock base, an 8-bit MCU to detect key presses and modulate the IR signal and an LED to generate the IR.

There are many modulation protocols but most are frequency or format variations of a few base protocols. Examples include amplitude modulation, frequency modulation or pulse modulation. For example, with pulse distance encoding, pulses remain the same length, while intervals between are either long or short (representing "0" and "1" respectively—Figure 1). This protocol is favored by Japanese consumer electronics companies and features a data payload of 8 bits address and 8 bits command, sent twice for reliability. In this example, a 9ms train pulse precedes the data, followed by a 4.5ms mark, then around 54ms for the address and command information. IR communication is typically one way. That means the remote has now way of knowing if the signal has been received.

The remote will dumbly repeat the command as long as a button is pressed. This example protocol provides repeat frames every 110ms, meaning the IR remote control is transmitting for perhaps 90ms during a half-second key press key press (Figure 2). At, for example, 50 key presses per day, that's a duty cycle of around 0.005 percent. While operating at, for instance, 2V, the remote draws around 100mW.

Negligible power is drawn while the remote is in "standby" mode. Two AAA cells connected in series, with a capacity of 900mAh, provide 2x1.5Vx900mAh = 2,700mWh. Assuming no DC-to-DC conversion (to keep costs down), and discarding voltage reduction as the battery ages, battery life is 2,700mWh/100mW = 27hr. However, with a duty cycle of 0.005 percent, users would not expect to change batteries for many months or even years.

However, while IR's simplicity, low-cost and low-power consumption has ensured its widespread adoption, the technology is not without its weaknesses. Imagine the consumer of a wall-mounted air conditioner for example; to change the temperature, the seated user either takes a chance that the IR will reflect from surfaces such as walls and ceilings or twist and turns to ensure his remote aims directly at the air conditioner to ensure alignment of IR emitter and receiver. How much easier would it be to just press a button, no matter what the positioning of the remote, for guaranteed communication?

In a second example, the proliferation of media centers—central PC-based entertainment devices serving as sources of music, video, and other digital files—finds consumers wanting to change volume, channel or website from another room where satellite TV, speakers or monitor are situated. Traditional IR remote controls rely on line-of-sight (or at least direct reflection) and have a range restricted to a few meters.

Third, consumers are increasingly demanding two-way communications. While it is theoretically possible to create two-way communication with IR, real life problems such as (light) interference and low data rate make this a poorly performing system. Moreover, attempting to incorporate two-way communications complicates the remote control's design, adds cost and drains battery power, canceling out the inherent advantage of the IR remote design.

An RF link solves the problem. Taking the media center example again, consider the user sat in her study listening to music; the media center is set to shuffle the digital music selection and an unfamiliar but pleasing track is played; with an RF link the user is able to casually glance at the remote's LCD to identify the track. She's also offered choices of "next track" (named), or "similar tracks of this genre" (again identified) or simply a "repeat" function. All this is enabled from the remote without even being in the same room as the source.

THE RF ALTERNATIVE
RF has been an option for remote control for some time (it was first used over a century ago) but until now the technology's relative expense, design complexity and power consumption have made it uncompetitive with IR for the vast majority of applications. However, the development of a new generation of low power RF transceivers has changed all that.

That said, the best-known low power RF technology, Bluetooth, is not a good fit for remote control applications. Because it was designed for high-speed file transfer between devices in a PAN (Personal Area Network), Bluetooth features a complex protocol with a large overhead (to ensure flexibility), reducing efficiency when payload throughput is low and increasing power consumption. Weighing in at 250kB, Bluetooth's protocol requires the resources of a relatively powerful MCU, increasing system cost.

A transmitting or receiving Bluetooth 1.2 chip's power consumption depends on the operating profile. But typical figures when running Bluetooth's Audio/Video Remote Control Profile (AVRCP) are in the 15mA to 30mA range. This is comparable with an IR remote control's chipset and LED.

Unfortunately, unlike the IR chipset and LED, Bluetooth continues to consume around 13mA of power even while the application is idle, dramatically shortening battery life. This is because Bluetooth has to maintain synchronization (a legacy of the technology's requirement to support up to seven slaves) to avoid re-linking delays by sending packets every 625µs (1,600packets/s, or a net data rate of 256kbps) to maintain the link, whether it's in use or not.

While Bluetooth does allow chips to enter a "sleep" mode to save power, it can take up to 3s for the link to be re-established—a level of "unresponsiveness" remote control users would find frustrating. Moreover, Bluetooth development is not trivial and can make it somewhat unwieldy for simple applications such as remote control. The use of Bluetooth means spending months getting the design ratified to ensure it meets the IEEE 802.15.1 standard. Finally, Bluetooth chips, while getting cheaper, are still expensive compared with proprietary transceivers.

A better solution for an RF remote control is an ultra-low power proprietary radio supporting a lightweight protocol customized for the application. This enables the designer to develop a robust RF system with battery life equivalent or better that that of an IR-based design. One example is Nordic Semiconductor's ultra-low power and inexpensive nRF24L01 2.4GHz transceiver with a specialized remote control protocol.

In comparison to Bluetooth, Nordic's nRF24L01 is a 2.4GHz GFSK (the same modulation technique as Bluetooth) transceiver, optimized for ultra-low power control and command applications. When transmitting, the nRF24L01's supply current is 11mA peak (at -0dBm output power, sufficient for 10m to 15m range), while in receive mode, peak supply current is 12.5mA.

When not transmitting, the nRF24L01 enters an ultra-low power standby mode, consuming just 0.9µA. The use of the dedicated remote control protocol reduces the idle current consumption to a negligible value; this is an important consideration for an application such as an RF remote control that sits idle for 99.995% of the time.

The very mention of RF design is usually enough to scare all but the most confident designer. But while it's true that RF design is not simple, vendors have worked hard to ensure it's no longer solely the domain of the RF expert. Very high integration in the transceiver, and the availability of development kits and reference layouts, makes it possible for any competent electronics design engineer to incorporate wireless hardware into their latest product.

However, the radio and hardware itself is only part of the solution; a robust RF protocol is crucial to produce an RF link that works well in the presence of other RF systems utilizing the ever more crowded 2.4GHz band. Consequently, a good RF solution not only depends on competent hardware design, but also demands a good knowledge of wireless protocol design.

WIRELESS CONNECTIVITY EVERYWHERE
While IR is the dominant technology for remote controls, it does have drawbacks such as limited range, lack of two-way communications and the requirement for line-of-sight communications. An RF remote control addresses all the weaknesses of an IR device: there is no need to point the device at the appliance to be controlled, the communication link is two-way, and wireless connectivity extends for into other rooms of the house and is unaffected by obstructions such as furniture, people or even internal walls.

Modern proprietary transceivers offer a cost-effective, ultra-low power, and simple way to implement wireless connectivity, and the RF design process has been simplified by reference design and ready-to-use customized protocols. Lucrative rewards await those prepared to make the leap to RF wireless connectivity. Designers find that once they've got to grips with the technique the imagination runs to how to implement RF wireless connectivity into all their future designs.


About the Author
Kjartan Furset is a senior application engineer at Nordic Semiconductor.
www.nordicsemi.no

Click here for Illustrations:

Figure 1, Figure 2