IR Remote Controls
How infrared remotes work — from Zenith's first wired system in 1950 to the universal remotes and smartphone IR blasters of today.
How IR Remotes Work
Every infrared remote control operates on the same fundamental principle: an LED emits pulses of invisible infrared light, and a photodetector in the receiving device converts these light pulses back into electrical signals. The pattern of pulses encodes the command being sent.
A typical IR remote contains a small microcontroller, a bank of rubber buttons, an IR LED (usually gallium arsenide, emitting around 940nm wavelength), and a simple oscillator circuit. When you press a button, the microcontroller generates a specific脉冲 pattern — a carrier frequency modulated with command data — that drives the LED.
The Carrier Frequency
Nearly all consumer IR remotes modulate their signal onto a carrier frequency between 36kHz and 56kHz, with 38kHz being by far the most common. This carrier serves two purposes: it allows the receiver to distinguish the remote's signal from ambient infrared noise (sunlight, incandescent bulbs), and it enables relatively long range despite the low LED power.
The receiver uses a PIN photodiode with an integrated bandpass filter tuned to the carrier frequency. This filter rejects IR signals at other frequencies, providing immunity to interference. Most receivers also include automatic gain control (AGC) to handle varying signal strengths as the remote distance changes.
Pulse Encoding
The actual command data is encoded by varying the timing of the carrier pulses. There are two main encoding approaches:
- Pulse Distance Encoding: The space between pulses carries the data. A short space means "0", a long space means "1". NEC protocol uses this method.
- Pulse Width Encoding: The duration of the carrier burst carries the data. A short burst means "0", a long burst means "1". Sony SIRC uses this method.
Each transmission typically consists of: an address code (identifying the device type), a command code (identifying the button), and sometimes a repeat code sent at regular intervals while the button is held down.
Line of Sight and Range
IR remotes require line of sight to operate because infrared light at 940nm cannot penetrate walls or most opaque objects. However, the signal can bounce off reflective surfaces like walls, ceilings, and furniture, which is why remotes sometimes work even when not pointed directly at the device.
Typical range is 5-10 meters for standard remotes, though high-power LED remotes can reach 30+ meters. The angle of operation is usually ±30° from the receiver's axis, though this varies by receiver design.
Evolution of IR Remote Technology
- 1950s: Wired remotes (Zenith "Lazy Bones") — physically connected by cable
- 1956: Flashmatic — visible light, directional, unreliable
- 1959: Space Command — ultrasonic (tuned aluminum rods), not IR
- 1977: Quasar remote — first practical IR system
- 1980s: NEC protocol standardizes IR communication
- 1990s: Learning remotes, universal remotes emerge
- 2010s: Smartphone IR blasters, HDMI-CEC reduces remote needs
- 2020s: IR persists for AV equipment; WiFi/Bluetooth for smart home
