Infrared (IR)

Quick-start checklist

1. Permission & scope: Only test on your own equipment or with explicit written authorization.
2. Receiver basics: Confirm target uses IR (not RF/Bluetooth). Check for line-of-sight.
3. Carrier & protocol: Many remotes use ~38 kHz carrier; determine likely protocol (NEC, RC5/RC6, Sony SIRC, Samsung, Panasonic, etc.).
4. Gear ready: One device with IR receive (learning) and transmit (emulation) capability.
5. Test plan: Start with non-disruptive commands (e.g., volume down on a spare TV), document results, then expand coverage.

IR protocol primer

IR remotes modulate infrared light (typically around 940 nm) at a carrier frequency (commonly 38 kHz) and send bursts of “on/off” pulses encoding addresses and commands. Different vendors use different frame layouts and timings.

Many consumer devices accept both “toggle” commands (Power) and discrete commands (Power On, Power Off), which are useful for reliable automation. Air conditioners often use long frames encoding entire state (mode, temp, fan), not just single buttons.

Common research workflows

1) Learn → Replay (universal remote basics)

• Use your tool’s IR learn function to capture a button press from the original remote.
• Save it with a readable label (e.g., tv_samsung_power).
• Replay to confirm the device responds; test from various angles and distances.

2) Protocol identification & library matching

• Attempt auto-decode; many tools can identify NEC, RC5/6, SIRC, etc.
• If decoding fails, record raw timings; search vendor code sets or community databases.
• Create a reusable “codebook” for your environment (TVs, projectors, AV switchers).

3) Discrete power & input selection for automation

• Prefer discrete ON/OFF/INPUT commands for reliable state machines (no “toggle confusion”).
• Chain sequences with delays (Power On → wait 3s → HDMI1 → Volume 12).
• Use line-of-sight considerations and stick an IR LED near the receiver in rack installs.

4) AC & HVAC remotes (state-full frames)

• Capture multiple frames (Cool 72°, Auto fan; Heat 68°) to learn full-state encodings.
• Replay known-good presets rather than trying to craft raw bits from scratch.
• Document brand-specific quirks (checksum bytes, temperature steps, swing modes).

5) Classroom / conference room hygiene (authorized)

• Build a “reset room” macro: Power Off all displays, mute amps, set inputs back to default.
• Create a “start meeting” macro: Power On projector, set HDMI input, unmute audio.
• Ensure you’re authorized; avoid affecting adjacent rooms or public spaces.

Hardening & defense notes

• Physical: Cover or recess IR receivers; use IR over IP inside cabinets instead of exposed front panels.
• Operational: Disable unused inputs and undocumented service menus; change default hotel/installer codes.
• Architectural: Prefer network-auth control (HDMI-CEC with policy, RS-232 over secure gateways) over open IR in sensitive areas.
• Environment: Place displays to reduce public line-of-sight; use occupancy/time policies for automatic power.
• Monitoring: If devices support logs, record state changes; unexpected bursts may indicate misuse.

Troubleshooting

• No response? Verify carrier (~38 kHz), polarity, and line-of-sight. Check fresh batteries on original remote.
• Inconsistent playback: Increase TX drive or place LED closer; add slight delays between repeats.
• Wrong device triggers: Some brands share code sets. Narrow LED aim or shield stray reflections.
• AC commands ignored: AC remotes often encode full state; capture a valid state frame and replay that exact byte sequence.

FAQ

Is IR line-of-sight only?

Yes—IR is light, so it typically requires line-of-sight. It can reflect off walls, but range and reliability drop.

What carrier frequency should I use?

38 kHz is most common, but some devices use 36/40/56 kHz. If learning works but replay fails, verify carrier frequency.

Can multiple displays be controlled at once?

Yes—wide-angle IR LEDs or multiple emitters can fan out signals. For precision, mount emitters directly on each receiver.

Useful references

• Vendor protocol primers (NEC, RC5/RC6, SIRC) and community IR code databases
• IR learner/emitter libraries for microcontrollers and SBCs
• Device manuals for discrete power/input codes (projectors, AV switchers, TVs)