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 pulse 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. Common IR receiver ICs (TSOP38238, VS1838B) include:
- PIN photodiode: Fast response time (~100ns), low capacitance. Sensitive to 850–1050nm wavelength, peak sensitivity at 940nm
- Bandpass filter: Typically 38kHz center frequency, ±5kHz bandwidth. Rejects DC sunlight and other IR sources
- AGC circuit: Automatic gain control handles signal levels from 5m (low power) to 30m (high power LED). Dynamic range ~40 dB
- Demodulator: Strips carrier, outputs digital pulse train to microcontroller. Output is active-low open collector
Standard carrier frequencies by protocol: 38kHz (NEC, Samsung, RC5/RC6), 36kHz (Sony SIRC), 40kHz (RC5), 56kHz (Philips). Mismatched carrier frequencies reduce range by 50–80%.
Major IR Protocols
Consumer IR Protocol Reference
| Protocol | Carrier | Bits | Encoding | Leader | Logic "1" | Logic "0" |
|---|---|---|---|---|---|---|
| NEC | 38 kHz | 32 | Pulse distance | 9ms mark + 4.5ms space | 560µs mark + 1690µs space | 560µs mark + 560µs space |
| RC-5 (Philips) | 36 kHz | 14 | Manchester (bi-phase) | Start bit (1) + field + toggle | Transition at center | No transition |
| RC-6 (Microsoft) | 36 kHz | 16/20/32 | Manchester | Header + mode + trailer | Transition at center | No transition |
| SIRC (Sony) | 40 kHz | 12/15/20 | Pulse width | 2400µs mark + 600µs space | 1200µs mark + 600µs space | 600µs mark + 600µs space |
| Sharp | 38 kHz | 15/20 | Pulse distance | 8× mark + 4× space | 560µs mark + 1690µs space | 560µs mark + 560µs space |
| JVC | 38 kHz | 16 | Pulse distance | 8.5ms mark + 4.5ms space | 560µs mark + 1690µs space | 560µs mark + 560µs space |
| RCA/Consumer | 57 kHz | 12/16/20 | Pulse width | 4ms mark + 4ms space | 1ms mark + 1ms space | 1ms mark + 2ms space |
| RCMM (MCE) | 36 kHz | 16/24 | Multi-pulse (4 levels) | Variable | 2-bit/symbol | 00/01/10/11 |
IR Protocol Details
- NEC: 38kHz carrier, 32-bit address + command (LSB first). 9ms leader burst + 4.5ms space. Logical "1": 562.5µs burst + 1687.5µs space. Most popular protocol — used by Samsung, LG, and many universal remotes. Repeat code: 9ms burst + 2.25ms space
- Sony SIRC: 36kHz carrier, 12/15/20-bit address + command. Pulse width encoding: "0" = 600µs burst, "1" = 1200µs burst. 400µs space between bits. Leader: 2400µs burst + 600µs space
- Philips RC5: 36kHz carrier, 14-bit Manchester-encoded. Bit time: 1.778ms. Two-level Manchester (transition = "1", no transition = "0"). Toggle bit flips on each keypress for debouncing
- Philips RC6: RC5 extended to 16/20/32-bit. Mode bit enables multi-device control. Used for Microsoft MCE remotes
- Samsung: 38kHz carrier, 32-bit (similar to NEC but different timing). Address repeated twice for reliability. Used by most Samsung TVs and soundbars
- RCMM: Multi-pulse encoding used by Microsoft Windows Media Center remotes. 2-bit per symbol (4 levels). 36kHz carrier
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.
- Manchester Encoding: Data encoded by transition timing rather than pulse width. Transition at bit center = "1", transition at bit edge = "0". RC5/RC6 use this — self-clocking, DC-balanced
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. Most protocols include a start bit or leader burst to synchronize the receiver.
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