In this blog post, let’s explore the principles behind how the TV remote controls we commonly use in our daily lives transmit signals via infrared communication and how they can accurately deliver commands even amidst external infrared signals.
When did TV remote controls first come into use?
Although TVs became commercially available in South Korea in the early 1960s, infrared-based TV remote controls didn’t begin to gain widespread adoption until much later, in the 1980s. Before that, people had to walk up to the TV to change the channel or used ultrasonic remote controls. Back then, since TVs offered far fewer channels and features than they do today, people likely didn’t feel much inconvenience without a remote control. However, as TV functions became increasingly diverse and the number of channels grew, the remote control became an essential tool for convenient TV use. Thanks to the remote control, we can now easily perform various functions—such as changing channels, adjusting the volume, and turning the TV on and off—without having to walk up to the TV. So, how exactly do these convenient remote controls work? Let’s take a look at the principle behind them.
There are several ways to transmit signals wirelessly, but TV remote controls typically use infrared communication. If you look at the front of a remote control, you’ll see a section covered in black, semi-transparent plastic; inside this section is an infrared emitter. When a button is pressed, the remote’s circuitry generates a signal corresponding to that button, and the infrared LED emits infrared light in accordance with that signal. The transmitted infrared signal is received by the TV’s infrared receiver, and the TV interprets the signal’s content to operate according to the remote’s commands. Infrared light has a longer wavelength than visible light and is therefore invisible to the human eye, but there is a way to verify whether an infrared signal is actually being transmitted: by using a camera. This is because a camera’s image sensor can detect some light in the near-infrared spectrum that is invisible to the human eye. If you point a camera at the front of the remote control and press a button, you can see the infrared emitter flashing a red light on the screen.
So why is infrared communication used? One reason is that it operates on very little power. Power consumption is so low that, once new batteries are inserted, a remote control can typically last for several months or more. In contrast, wireless microphones used in karaoke rooms rely on radio waves for wireless communication, and depending on battery capacity and usage patterns, they may need recharging after a few hours of use. Of course, wireless microphones and TV remote controls differ in power consumption, communication methods, and battery capacity, so a direct comparison isn’t possible; however, it’s clear that remote controls communicate using very little power. This low-power characteristic plays a key role in allowing us to go for hours without having to replace the remote control’s batteries.
How are infrared signals distinguished from other signals?
However, there was a problem that needed to be solved in order to use infrared communication. This is because infrared radiation isn’t emitted only by remote controls. Infrared radiation is emitted not only by the sun outside the window but also by indoor lighting. In fact, the spaces where we live are filled with infrared radiation from various light sources. Furthermore, since a TV’s infrared receiver is designed to detect even very faint signals, there is a possibility of malfunction due to external light. Despite this, how do remote controls operate without major issues? One of the secrets lies in frequency modulation.
Remote controls do not simply turn infrared on and off; instead, they transmit signals by rapidly modulating the infrared signal to a carrier wave of a specific frequency. In standard infrared remote controls, a carrier wave of around 38 kHz is widely used, and the TV’s receiver is designed to detect signals primarily within this specific frequency band. Simply put, at 38 kHz, the infrared light is rapidly turned on and off about 38,000 times per second. This allows the remote control to distinguish its signals from external light sources—such as the sun or artificial lighting—that simply emit infrared light, thereby reducing malfunctions caused by external light.
So, how do TV remote controls transmit signals? While TV manufacturers use different communication standards, this article will focus on Sony’s SIRC standard.
How are 0s and 1s represented in the SIRC standard?
Since infrared communication is a form of digital communication, it transmits information by sending 0s and 1s as signals. In the SIRC standard, a single bit is represented by a combination of an infrared signal of a fixed duration and a gap where no signal is present. Here, “ms” stands for milliseconds (one-thousandth of a second), and “μs” stands for microseconds (one-millionth of a second). In SIRC, a logical 1 is represented by emitting an infrared signal for approximately 1.2 ms, followed by a 600 μs gap without a signal; a logical 0 is represented by emitting an infrared signal for approximately 600 μs, followed by another 600 μs gap without a signal. The SIRC carrier frequency is typically around 40 kHz. Therefore, the appearance of vertical stripes during the infrared emission period does not mean the infrared light is continuously on during that time; rather, it is flashing very rapidly in sync with the 40 kHz carrier frequency. Because it flashes at such a high speed, it appears as vertical stripes in the image. This is the basic method of signal construction in the SIRC standard, and various commands can be sent by combining these 0s and 1s.
There are several versions of SIRC, such as 12-bit, 15-bit, and 20-bit; the most basic 12-bit format consists of 7 bits of command information and 5 bits of device address information. Before sending a single data packet, a start signal is transmitted first, consisting of an infrared signal lasting approximately 2.4 ms followed by a 600 μs pause. This allows the receiver to recognize that data transmission is about to begin. The seven consecutive 0s or 1s that follow indicate which command the remote control has sent. This can be thought of as a 7-digit binary number, where the MSB (Most Significant Bit) represents the highest digit and the LSB (Least Significant Bit) represents the lowest digit. Since SIRC transmits bits starting from the LSB, it is necessary to distinguish between the actual transmission order and the order in which humans read binary numbers. For example, if the bit sequence for a specific command is represented as the binary number 0010011, converting this to decimal yields 19. The SIRC standard defines specific actions—such as lowering the volume—based on these command codes. The five subsequent 0s or 1s represent the device’s address. This information is used to distinguish which device should respond to a given signal in an environment where multiple devices use the SIRC standard. Both the remote control and the device have corresponding address information, and TVs are designed to respond only to signals carrying their specific address. This helps minimize issues such as accidentally operating other nearby devices or interference between signals from different remote controls.
The Technology Hidden Inside a Familiar Remote Control
While this article has focused on the SIRC standard, other infrared communication standards also operate on fundamentally similar principles. We tend to underestimate the complexity of things that are commonplace. Since remote controls are familiar objects we see everywhere, we might think of them as nothing special. However, hidden within them is a complex process: the moment a button is pressed, the command is converted into a digital signal, transmitted as an infrared signal, and then interpreted by the TV’s receiver, which distinguishes it from external light. The reason the TV responds immediately when we press a button without a second thought is that these communication principles are implemented with great precision. Ultimately, the remote control—which we use so conveniently in our daily lives—is the result of developers’ careful consideration of user convenience and their technical efforts.
