Press Backgrounders

RF remote control as a replacement for IR remote control

Nordic Semiconductor’s nRD24H1 RF Remote Control Reference Design is the ideal starting point for designers wanting to take advantage of RF’s advantages over Infrared for modern remote controls. The Reference Design integrates all critical functions and is relatively simple to develop into many different remote control concepts. With the hardware design and optimization done, a remote control design team can focus on the application functionality needed to make their remote better than the competitions’

 

Infrared (IR) wireless communication is simple to design-in, robust, cheap to manufacture and yields a controller that can run for months on two-to-four AAA 1.5 V 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). Contemporary consumers demand a user interface on their remote offering intuitive instructions and information about the media they’re listening to or watching.

 

RF remote controls promise to finally match the convenience of IR – namely 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.

 

IR exposed

 

IR is electromagnetic (EM) radiation of wavelengths longer than visible light, but shorter than RF spanning three orders of magnitude between 750 nm and 1 mm. 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 (see figure 1). 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.

 

Figure 1. Schematic illustrating IR modulation and demodulation

Figure 1. Schematic illustrating IR modulation and demodulation

 

A simple IR remote comprises 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 – see figure 2). This protocol is favoured by many consumer electronics companies and features a data payload of 8 bits address and 8 bits command, sent twice for reliability.

 

Figure 2: IR remote pulse distance encoding protocol

Figure 2: IR remote pulse distance encoding protocol

 

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 (see figure 3). At, for example, 50 key presses per day, that’s a duty cycle of around 0.005 percent.

 

Figure 3: Pulse distance encoding full sequence structure

Figure 3: Pulse distance encoding full sequence structure

 

...to continue reading this technology backgrounder, please download the PDF

 

The complete document is 2,100 words and includes sections on: IR exposed, and The RF alternative.