Solid on
Connected to a transmitter, or bootloader mode
- Cause
- Normal connection; bootloader is also possible on single-colour receivers
- Fix
- Confirm the ExpressLRS Lua script shows C and verify stick movement before flight.
Draft guide — under review
Binding ELRS, and what the LED means
A draft reference for binding, receiver indications and the book's channel map. Confirm the exact radio, receiver, firmware and power arrangement against their documentation. Equipment-specific procedure checks remain pending; a working link is not first-flight approval.
What this covers
- Radios
- RadioMaster Boxer and Pocket with internal 2.4 GHz ExpressLRS, not 4-in-1 or CC2500 variants
- ExpressLRS firmware
- ExpressLRS 4.1.0 documentary reference; preserve compatible installed firmware
- Receivers
- Original Matrix 1S 3IN1/5IN1 onboard UART ELRS, RP1, RP2, RP4TD, EP1, EP2 and BETAFPV Nano - 2.4 GHz UART variants only; identify exact revision, actual compatible firmware and LED type; not an SPI setup recipe
- FC firmware and App
- Betaflight firmware 2025.12.5 and Betaflight App 2025.12.2 are separate documentary references, not a qualified installed pair. Record actual target/build and served App version. Older 4.5.x/legacy Configurator and other release lines remain separate contexts; do not flash an original Matrix or another receiver/FC merely to match this reference.
Before power. Before any receiver power-up: remove props with all power disconnected. Identify the exact board/receiver and documented supply route first; keep ARM/PREARM off and throttle low. A powered video transmitter needs its specified antenna and cooling. Stop if the wiring or permitted power sequence is uncertain. This draft is not a first-flight or failsafe sign-off.
Revised print sheet pending — view status
The reviewed ExpressLRS 4.1.0 documentary reference; preserve compatible installed firmware route needs compatible TX-module and RX firmware on the same major line: 4.x does not bind to 3.x. EdgeTX and the Lua tool are different software, not those two firmware identities. Do not flash working compatible equipment merely to match this page. Record actual identities and use their supported instructions.
The receiver LED decoder
The blink-pattern decoder covers single-colour receiver status LEDs only, not RGB receiver or transmitter LEDs. Use the exact device's documentation for those. Darkness or a flicker alone does not establish a fault or prove that power is disconnected.
Slow blink (500 ms on/off)
Waiting for connection from the transmitter
- Cause
- Radio off, incompatible major versions, bind phrase mismatch, or link not established
- Fix
- Power the radio, then verify the major versions and bind phrase match.
Fast blink (25 ms on/off)
WiFi mode enabled
- Cause
- Receiver entered WiFi update mode
- Fix
- Use the WebUI for the intended task. To leave it, follow the documented restart route and check retained pairing; reconnection is not guaranteed.
Double blink, then pause
Binding mode enabled
- Cause
- Receiver was deliberately put into traditional bind mode
- Fix
- Use Bind in the compatible Lua tool. For Persistent storage with no new bind completed, restart cancels the attempt; Volatile restarts unbound.
Triple blink, then pause
Connected, but Model Match configuration does not match
- Cause
- The receiver's Model Match ID differs from the active radio model's Receiver ID
- Fix
- Verify the intended model, IDs and On/Off state while connected, then recheck channels. Do not disable a deliberate identity safeguard just to make the bars move.
Medium blink (100 ms on/off)
Radio chip not detected
- Cause
- Receiver hardware or firmware cannot communicate with its RF chip
- Fix
- Stop and retain the exact target/version and update log, if any. Follow the receiver manufacturer's recovery guidance; do not try unrelated targets.
Off, no LED
No visible status indication
- Cause
- Power, hardware or indicator state must be checked; darkness alone is not a diagnosis
- Fix
- Isolate battery, USB and every other supply before inspection or continuity/resistance work; follow stored-energy instructions. A beep is not a short-circuit verdict. Live voltage measurement requires the exact documented rail, suitable meter setup and qualified safe test points; do not assume every receiver rail is 5 V.
Brief flicker
Possible supply interruption
- Cause
- Investigate supply and device state; a flicker alone does not establish a brownout
- Fix
- Stop powered testing and investigate the documented supply/load arrangement. Voltage tests need qualified live-measurement conditions; inspect/rework only after all power is isolated. A uniformly dull SAC305 surface alone is not a fault. A brownout invalidates failsafe acceptance.
Anything else
Hardware-specific status
- Cause
- Vendor-specific pattern
- Fix
- Check the exact receiver and LED documentation; do not borrow a transmitter or RGB pattern.
Set the radio up first
Prepare the radio with aircraft off
Follow Chapter 11's Prepare the flight model without powering an aircraft before this binding reference. It owns backups, the exact Boxer controls, model selection, Lua access and restart readback. Keep SIM-USB RF-off. Pocket needs its own physical-control map, not Boxer switch letters.
Preserve or create separately
Keep a compatible working model's channel map, Receiver ID, firmware, RF settings and compatible Lua file unchanged. A new model uses a separate slot and unused recorded ID; a different name does not separate a copied ID or module-global pairing phrase. Do not upgrade to resemble an example.
Identify EdgeTX and Lua fields separately
For the new v2.12/4.1 Boxer example, Internal CRSF, External OFF, Receiver number and Arm using CH5 are EdgeTX model settings. Rate, switch transport, telemetry ratio and power are module Lua settings. Selecting an RF-enabled model can transmit before Lua opens: establish antenna, permitted startup RF state and operating conditions first.
Retain the pairing identity
An already compatible working pair needs no new bind. Preserve an existing TX pairing identity when adding an aircraft; changing its phrase can affect other models. If choosing a new phrase, ExpressLRS recommends at least eight alphanumeric characters. This derives a UID, not authentication or encryption. Chapter 8 owns endpoint compatibility and the connected route.
Compare the actual RF plan
The new example selects 2.4 GHz LoRa 250Hz(-108dBm), Wide, Std and permitted 25 mW maximum with Dynamic Dyn. Those are preparation choices, not range or warning acceptance. Compare a preserved compatible model with its own supported record instead; do not force a working Hybrid plan through the new-model table. Equal Hz does not mean equal RF mode.
Restart and return to the aircraft checks
Complete the owner's branch-specific normal shutdown, cold readback and independent backup. Closing Lua does not undo a confirmed write; there is no separate ELRS Save command to invent. Then use Chapter 8's compatible endpoint/pairing route and Chapter 11's protected receiver observation. C alone does not prove that control frames reach Betaflight.
The bind phrase. Enter the same case-sensitive phrase on the ELRS transmitter module and receiver, without accidental spaces. It derives their pairing UID; the literal phrase need not remain readable on either device. Matching UID is not the whole check: band, firmware compatibility and Model Match still matter.
Bind the receiver
Preferred — bind phrase
- Skip rebinding an already compatible working pair. When adding a receiver to an existing transmitter identity, retain that TX identity and use Chapter 8's corresponding receiver-side pairing route. Do not replace the module-global TX phrase to match a new aircraft model name.
- If deliberately establishing a new pairing identity, use each identified device's WebUI to enter the same phrase. A compatible 4.1 Lua tool can also set the TX phrase or a connected RX phrase; an unbound RX is not reachable through that link. A change/restart can break the link; reach the other endpoint through its own WebUI if needed. Follow the save/restart prompts. Flashing is not needed to set a phrase.
- For this ordinary personal-model route, confirm receiver Bind Storage is Persistent. Power the radio, then the receiver through its documented supply route. After a safe power-cycle, verify the intended pairing again.
- For a single-colour receiver LED, a slow blink means it is waiting. Solid can mean connection or bootloader mode; confirm the ExpressLRS Lua script shows C and complete the receiver checks before flight.
Fallback — traditional binding
- In the reviewed 4.1 firmware, a stored phrase/UID does not by itself prevent manual binding. Confirm Persistent storage for this route. Volatile forgets the bind after restart; Returnable loans and Administered storage are separate managed routes. Administered blocks ordinary manual-bind entry; do not override a managed policy.
- With the transmitter off and the receiver's power route established, power on then off within two seconds, repeat once, then power on a third time and leave it on. Stop if the expected bind indication does not appear; do not keep cycling blindly. A supported receiver button, Betaflight Bind Receiver / bind_rx, or connected-RX Lua command is an alternative only when its exact hardware/firmware instructions apply.
- For a single-colour receiver, confirm double blink/pause. Power the radio and select Bind in its compatible ELRS Lua tool. Confirm C, then the intended FC channels, not just a solid LED. Verify the retained bind after a safe restart. Do not rebind to bypass a Model Match mismatch.
Verify in Betaflight
- Start props-off and fully isolated. Identify the exact board/receiver, wiring, installed firmware and App. For the book's selected original Matrix, Kakute/Tekko and GOKU routes, complete Chapter 11's "Before receiver observation: exclude motor beacons", then follow its complete "Receiver observation: protected power, radio on" sequence. That state keeps the wired Finder and removable video disconnected, the independent Beacon off, motor override disabled, and ARM/PREARM off. It does not establish another BNF or receiver's power arrangement.
- For this UART receiver route, check Serial RX on the receiver's documented UART and Serial (via UART) / CRSF in Receiver. SPI receivers are a separate route. Keep RSSI Channel Disabled and RSSI ADC off for ordinary ELRS CRSF link statistics.
- Use USB alone when it supplies valid receiver data. For a selected build that needs battery power, use only the corresponding protected branch in that Chapter 11 sequence, including its pack-voltage limit, load state and shutdown order. Do not transfer that recipe to other hardware. A missing channel can also mean a model, binding, UART or wiring error; it is not permission to bypass protection or raise its current setting.
- Move one stick axis at a time. Confirm the correct labelled channel, direction, centre and both endpoints; normal throttle stays low except during its qualified disarmed channel check. AETR and TAER are mappings to verify, not competing safety grades. Do not adjust limits just to match an illustrative number.
- Exercise only intended non-arming controls and compare each physical position with its actual channel and active range. Keep ARM/PREARM off throughout receiver observation. For the standard route, CH5 / AUX1 low means disarm and high requests arm; this explains the assignment, not an instruction to move ARM here. ARM/PREARM transitions and RF-loss testing belong to the separate USB-disconnected normal-radio check. A highlighted Modes row does not prove arming or a physical function.
- If channels do not move, record Model Match, model mixes, receiver power, wiring, protocol and UART state before changing anything. Finish with throttle low, ARM/PREARM and BEEPER off; complete the selected procedure's App Disconnect and all-source shutdown before editing or changing connections. Channel bars do not replace Chapter 8/11's separate normal-radio and first-flight checks.
Model match. Model Match is optional and must be deliberately configured and checked. When enabled, the receiver's stored Model Match ID must agree with the selected radio model's Receiver ID. A mismatch can leave an RF connection but withhold control frames from the FC; it is not an FC arming command. Record the On/Off state and IDs, then verify channels for each intended model. Turning it off on the TX alone need not clear the receiver's stored ID.
Update only for a reason; recover deliberately
Identify before updating
Record radio/EdgeTX, Lua-tool version, ELRS TX and RX model/target/version, and FC firmware separately. Read TX firmware near the Lua page bottom; read RX identity from its WebUI or supported connected Other Devices view. Distinguish UART from SPI RX. Compatible working equipment does not need a flash to match this sheet. Retain settings and the reason for any update.
Choose the correct device route
UART RX updates may use supported Wi-Fi, BetaflightPassthrough through the FC, or direct UART. TX updates use their own supported Wi-Fi/UART or EdgeTXPassthrough route, not Betaflight receiver passthrough. SPI RX support belongs to its FC firmware. Verify the exact target, supported release and regional options; never force a target mismatch or use a look-alike target.
Preserve the result and stop on failure
Close competing serial tools and qualify power/antenna/cooling first. Wi-Fi mode may use a saved network rather than show an access point; receiver auto-Wi-Fi depends on its connection state and configured delay. Keep the updater log and read back the device identity after completion. On failure, retain the error and stop; a solid LED is not proof of success. Follow that exact device's recovery guide, not repeated blind flashes.
Rejoin the checks
Before returning to flight, recheck pairing/storage after restart, the intended Model Match IDs, channel directions and ranges, and deliberate ARM-off state. Repeat the affected props-off checks and separate normal-radio failsafe validation in Chapters 8/11. Binding or an updater success message does not approve flight. End bench work disarmed and fully isolated.
Read the control link, not just one number
- Uplink LQ (%)
- For ELRS 4.1.0 2.4 GHz LoRa 250 Hz: percentage of recent receive periods with a valid uplink packet, including sync/data, not just RC commands. Repetition modes can account differently. High LQ proves neither FC control delivery nor safe range; downlink LQ is separate.
- RSSI dBm and margin (dB)
- Received signal power is in dBm; margin above the exact mode's sensitivity limit is a difference in dB. For example, -100 dBm with a -108 dBm limit gives 8 dB margin, not a flight threshold. Use the correct band, modulation, packet mode and firmware reference.
- RF mode / rate prefix
- A mode identifier is not a frequency in Hz. For the pinned ELRS 4.1.0 2.4 GHz LoRa 250 Hz enum and Betaflight 2025.12.5 CRSF Link Quality formatter, 27:99 means RF mode 27 and 99% uplink LQ. This is a source example, not observed pixels or a mapping for every version.
- SNR and returned telemetry
- SNR is signal relative to noise, in dB, not LQ percent. Returned telemetry carries receiver readings back to the radio; its loss or update rate is not identical to uplink control loss. The FC's local CRSF link-statistics feed is a different path from that RF downlink.
Configure and verify the actual radio sensors, audio rules and FC/OSD indications separately. No automatic spoken LQ warning is promised. Chapter 11 explains the version/mode-specific readings; no single LQ percentage or dBm value here grants safe-flight clearance.
An example AUX channel plan
This is an example plan for the standard Arm using CH5 route, not a universal radio preset. Physical switch labels differ between radios. In Hybrid/Wide, CH5 is two-state; other AUX channels have mode-specific resolution and update timing. Full Res changes channel availability and ranges, so recheck the plan after any mode change. Record actual channels and observed values; the ranges below are examples, not installed readback. This table describes assignments, not a switch-test sequence. Keep ARM/PREARM off during receiver observation; their transitions belong to the separate normal-radio check.
| Channel | Mode | Switch | Active range |
|---|---|---|---|
| AUX1 (ch 5) | ARMLow is off, high requests arming. PREARM and all other FC arming checks still apply. | Deliberate two-state ARM control; record its label | 1750–2100 |
| AUX2 (ch 6) | ANGLEOptional; verify the actual flight-mode plan. | Recorded flight-mode switch | 1750–2100 |
| AUX3 (ch 7) | PREARMA trim or momentary button does not automatically output an AUX channel. Verify held and released states and the complete PREARM-to-ARM sequence; a short pulse can be missed. | Separate deliberate control with a verified channel mix | 1750–2100 |
| AUX4 (ch 8) | BEEPER | Recorded beeper switch | 1750–2100 |
| AUX5 (ch 9) | BLACKBOX | Recorded logging control, if configured | 1750–2100 |
| AUX6 (ch 10) | GPS RESCUEAdding GPS alone does not qualify Rescue. Keep this unassigned until its separate hardware, configuration and practical validation are complete. | Unassigned on selected no-GPS builds | Not assigned |
| AUX7 (ch 11) | FLIP / TURTLEOptional exact-hardware-qualified feature only. Disarm before selecting or leaving crash-flip mode; keep throttle low. No automatic return-to-flight after a crash (Ch08/14). | Unassigned until separately qualified | Not assigned |
| AUX8 (ch 12) | Spare / reserved | — | — |
You may choose a different physical ARM switch, but keep its mix on CH5 / AUX1 for this route. CLI AUX index 0 means AUX1, not channel 0. Define each mode from observed values; the lower range bound is included and the upper bound excluded in the pinned firmware. Compatible modes may be active together; unintended shared-switch activation is the problem, not all overlap.