Wiki / References
📡 Frequencies, wavelengths & brightness
The physical layer of every optical LEGO link: what each source emits and what its receiver expects. Match an emitter to a row via Hardware shopping list.
✅ = officially documented / strongly sourced · ≈ = community/typical value · ❓ = not publicly published.
Optical links
| Link | Carrier | Wavelength | Receiver | Notes on brightness |
|---|---|---|---|---|
| VLL (Micro Scout / Code Pilot / Scout) | none — baseband ✅ | *visible or IR ✅ (sensor is broadband; LEGO's tower drove VLL on a visible-red* LED — IR works too, confirmed on-device) | broadband light sensor (silicon, IR-sensitive to ~1100 nm) | needs high ON/OFF contrast; close range, dim room helps; torch works at scale 1.05–1.35× |
| RCX | 38 kHz OOK serial (2400 baud, 8O1) — bit '0' = 417 µs burst of 38 kHz, bit '1' = 417 µs off | ≈940 nm IR | 38 kHz demodulator (TSOP-class) | needs a modulated IR LED (not a bare on/off one); aim at the RCX eye. (Corrected: RCX does use a 38 kHz carrier — confirmed by the canonical mralligator protocol spec + working DIY towers maehw/DiyIrTower & mattallen37.) |
| Power Functions | 38 kHz ✅ | ≈940 nm IR ≈ | 38 kHz demodulator (TSOP-type) | range up to ~10 m; standard IR-remote optics |
| 76 kHz IR family (Spybotics, Manas, RC Nitro, DUPLO Dozer, early RC Train) | 76 kHz ✅ | ≈940 nm IR ≈ | 76 kHz demodulator | 3 channels (Manas); short-lived |
| EV3 IR (sensor + beacon) | 38 kHz ✅ (LPF RC / Power Functions protocol; beacon adds heading/distance codes) | ≈940 nm IR ≈ | EV3 IR sensor / PF receiver | 4 channels; proximity ~70 cm; PF remote ↔ EV3 cross-compatible |
Optical sensors (sensing, not comms)
| Sensor | Emits | Reads |
|---|---|---|
| RCX light sensor | red LED (≈625–660 nm) ≈ | reflected / ambient light |
| NXT light sensor | red LED ≈ | reflected / ambient |
| NXT 2.0 / EV3 color sensor | R + G + B LEDs ✅ | colour ID, reflected, ambient |
| WeDo motion sensor | IR ≈ | reflection (proximity) |
| Powered Up Color & Distance (88007) | visible (colour) + IR (distance) ≈ | 6 colours, distance ~5–10 cm ✅ |
Practical rules
- VLL = bare LED blinked on/off. A visible white/red LED or an IR LED both work (no carrier).
- *PF (38 kHz) and 76 kHz family need a modulated IR LED* at that carrier (a normal IR-remote emitter), driven by a library — a bare on/off LED won't be decoded.
- Invisible programming of a VLL brick → IR LED at 850 nm (best silicon response, near-invisible) or 940 nm (fully invisible, weaker) → IR LED (invisible VLL).
- CyberMaster is radio (27 MHz), not optical → CyberMaster.
See Hardware shopping list for matching emitters/receivers.