SkyRelay Conduit

1. Regulatory Compliance

LilyGo T-SIM7600NA

2. Product Overview

The SkyRelay Conduit is a compact, LTE-connected telemetry gateway for unmanned aircraft systems. It streams real-time flight data to the SkyRelay cloud over cellular from anywhere with LTE coverage.

Key Features

• LTE Cellular Telemetry — real-time MAVLink telemetry over 4G LTE via Hologram global SIM
• MAVLink TCP Relay — connect Mission Planner, QGroundControl, or any GCS over the internet
• Local Bluetooth GCS Link — connect QGroundControl or Mission Planner directly over Bluetooth, alongside the cellular link
• MQTT Cloud Streaming — telemetry published every second to the SkyRelay cloud
• MAVLink 2 Message Signing — built-in HMAC-SHA256 signing rejects unauthorized commands
• Remote ID Scanner — BLE scanner detects nearby ASTM F3411-22a Remote ID broadcasts
• OTA Firmware Updates — update firmware over-the-air from the dashboard
• Data Saver — batches telemetry into fewer packets to cut cellular data usage
• Companion Battery Monitoring — onboard 18650 Li-ion cell
• Audible Buzzer Alerts — Morse beep sequences for boot, cloud connect, SOS, and lost drone finder
• Lost & Found QR Recovery — mark your drone lost/stolen so finders can contact you via the QR code
• Web Dashboard — live telemetry, map, commands, and device settings
• Backup Power — the Conduit runs off its 18650 battery, which charges from the FC cable during flight or from USB-C on the bench. If the Conduit loses power during an incident, it keeps transmitting GPS location facilitating recovery.

Supported Autopilots

• ArduPilot (Copter, Plane, Rover) — all versions with MAVLink
• PX4 — all versions with MAVLink

3. What's in the Box

Plug & Fly Kit (K01)

Ready to use — continue with Getting Started (Section 6).

BYOD Kit (K02)

You supply the LilyGo T-SIM7600NA board and an 18650 battery. Case print files and firmware are downloads. Assemble first — see BYOD Assembly (Section 5).

4. Supported Hardware

LilyGo T-SIM7600NA

Used in the K01 (integrated) and K02 (BYOD — you supply this board) kits. See What's in the Box (Section 3).

The Conduit is built on the LilyGo T-SIM7600 development board.

LED Indicators

5. BYOD Assembly & Wiring Diagram (K02 only)

1. Attach your LTE and GPS antennas to the LilyGo board
2. Flash the SkyRelay firmware over USB-C — www.skyrelay.us/conduit/firmware.html
3. Insert the Hologram SIM in the nano-SIM slot (underside of board)
4. Fit an 18650 battery in the holder
5. Solder the 3-pin Dupont harness to the buzzer
6. Connect the buzzer harness: V → 3.3V, G → GND, I/O → GPIO 22 (see Figure 2)
7. Solder the 4-pin UART board to the 2-pin Dupont harness and the battery input cables that ship with LilyGo
8. Connect the UART pan board harness: GPIO 18 (TX), GPIO 19 (RX), GND (see Figure 2)
9. Print and fit the case
10. Assemble unit

6. Getting Started

K01 units arrive fully assembled and ready to be used. K02 and BYOD builds: complete Section 5 first.

Flight Controller Wiring Diagram

Step 1: Match the Cable to Your Flight Controller

The 4-pin UART-to-FC cable must match your FC's telemetry port pinout. Order the pins in the connector as shown in Figure 3:

• Power and ground go to their counterparts
• Conduit RX → FC RX, Conduit TX → FC TX (the cables are reversed inside the case)

Step 2: Configure TELEM Settings

The Conduit communicates with the flight controller over MAVLink serial at 115200 baud. Set the parameters as follows, where n represents the serial port on your flight controller:

• ArduPilot (e.g., SERIAL2): SERIALn_PROTOCOL = 2, SERIALn_BAUD = 115
• PX4 (e.g., TELEM2): MAV_1_CONFIG = TELEM 2, SER_TELn_BAUD = 115200

Step 3: Plug In and Mount

Plug the cable into the FC telemetry port and mount the Conduit on the airframe with the straps.

Step 4: Power On

Turn the power switch ON:

1. · · · · · · (HI) — buzzer confirms firmware is running
2. Bluetooth becomes available for a local GCS connection (Section 12)
3. Cellular modem connects to LTE
4. Cloud connected — — · — (K) confirms telemetry is streaming

Boot typically completes in 30–60 seconds. If you hear HI but never K, the device is not reaching the cloud — check LTE signal and subscription status.

Step 5: Activate

1. From a mobile device log into your SkyRelay account
2. Scan the QR code on the Conduit case and/or the activation card
3. Click Activate

Step 6: Verify Telemetry

Open the dashboard and confirm live telemetry is flowing — GPS position, flight controller heartbeat, and Conduit status update every second.

Buzzer Reference

7. SkyRelay Dashboard

Real-time monitoring and control of your Conduit and connected aircraft, at your SkyRelay account URL after activation: app.skyrelay.us/devices/

Monitor Tab

Live data updated every second:

• UAV Status — armed/disarmed, flight mode, system state
• GPS — latitude, longitude, altitude, satellites, fix type, accuracy (HDOP)
• Speed & Motion — ground speed, climb rate, throttle
• Home — home position and live distance to home
• Attitude — roll, pitch, yaw
• Flight Battery — voltage, current, remaining percentage
• Conduit Status — LTE signal, firmware version, Link RTT, device health
• Companion Battery — voltage, percentage, charging status
• Nearby Aircraft — Remote ID detections with position, speed, and signal strength

Command Tab

Live position on an interactive map — location, heading, altitude.

Settings Tab

• GCS Relay — stream flight data to your GCS over cellular; off to save data
• Data Saver — batch MAVLink into fewer packets to cut cellular data; small added latency
• Secure MAVLink — enable MAVLink 2 signing and manage the key (Section 11)
• Enable Buzzer — master mute/unmute
• Alert on Signal Loss — SOS when LTE drops (off by default)
• TEST BUZZER — plays K to confirm wiring
• Voice Alerts — spoken armed/disarmed and FC connect/disconnect on the Command page
• Lost / Stolen — reveal contact methods to finders via the QR code (Section 8)
• Device Info — serial number, firmware version, IMEI, environment

8. SOS Alerts and Lost Drone Recovery

Two independent ways to trigger an audible SOS (· · · — — — · · ·) on the onboard buzzer. Both also mirror the SOS to the flight controller's ESC buzzer for a much louder locator tone.

Mode 1 — Signal Loss Failsafe (automatic)

For the worst case: the drone goes down, LTE drops, and the dashboard is unreachable.

Enable: Settings → Alert on Signal Loss. Saved permanently in the device — enable once, it stays on across reboots.

On signal loss: the buzzer sounds SOS every 10 seconds (the gap conserves battery — it can keep sounding for hours). When LTE reconnects, the SOS stops automatically.

Mode 2 — Lost Buzzer (manual)

For when you still have LTE — e.g., the drone is down in tall grass and you're walking to it.

Activate: Ops → Lost Buzzer (button turns red). SOS every 2 seconds. Press again to stop.

FC/ESC Buzzer

During any active SOS, if the drone is disarmed and the FC is connected, the Conduit sends a tone command to the FC every 4 seconds. On ArduPilot with DShot ESCs (NTF_BUZZ_TYPES includes DShot), the motor coils play the tone — much louder than the onboard piezo. Suppressed while armed.

Summary

Mode 3 — Drone Found After a Flyaway Incident

Each Conduit has a unique case code embedded into the QR code on the unit. It serves as a quick way to log into the dashboard of that Conduit, and it allows individuals who found the drone to scan the QR code and report it found.

How It Works

A finder who scans the code sees Report Found Drone. What happens next:

Setup

1. Settings → Lost / Stolen → toggle the master switch on
2. Choose contact methods to share: Email (account email), Call / Text (your phone number), Other (free text, e.g. “DM @handle on Instagram”)
3. Settings save automatically

Toggle off to immediately hide contact info; the settings are kept for next time. Contact info is never shown until the finder clicks “Report Found Drone” and the toggle is on.

9. Firmware Updates

Three ways to update Conduit firmware: over-the-air over the cellular link, one-click over USB from a browser, or manually over USB with esptool.

Over-the-Air (OTA)

Firmware updates install over the LTE connection — no cable or physical access needed. The Conduit checks for updates on boot; the dashboard shows current and available versions.

Installing:

1. From the dashboard, send the ota_update command
2. The Conduit plays · · — (U) and downloads the firmware over LTE; progress shows in the dashboard
3. After verification it plays three long beeps and reboots into the new firmware
4. If the update fails, it rolls back to the previous version automatically

WebSerial (USB)

One-click flash over USB-C, straight from a browser — no OTA connectivity required. Use this if the Conduit has never come online, or as a fallback when OTA fails.

1. Go to www.skyrelay.us/conduit/firmware.html in Chrome or Edge
2. Connect the Conduit via USB-C
3. Click Flash and select the device's serial port when prompted
4. Device reboots with the new firmware

CLI (esptool)

Manual flash from the command line — works in any browser environment or where WebSerial isn't available.

1. Download the .bin file for your version from www.skyrelay.us/conduit/firmware.html
2. Connect the Conduit via USB-C
3. Flash with esptool: esptool.py write_flash 0x10000 firmware.bin
4. Device reboots with the new firmware

10. Remote ID Scanner

A BLE scanner detects nearby aircraft broadcasting ASTM F3411-22a Remote ID. Its purpose is proof that the Remote ID module on the attached drone is present and broadcasting. Detections appear under Nearby Aircraft in the dashboard.

• Scans continuously (3-second interval), tracks up to 8 aircraft, entries expire after 30 s
• Reports UAS ID, ID type, aircraft type, position, altitude, speed, heading, and signal strength (RSSI)

11. MAVLink Relay Security

The SkyRelay cloud assigns each Conduit a unique UDP port (14550–14649) at provisioning. Your GCS connects to this port. Because it accepts unauthenticated UDP, protect it: anyone who can reach the port could inject MAVLink commands.

1. Don't Share Your Connection Details

Your relay address and port are unique to your drone — treat them like a password. Share only with authorized GCS operators.

2. Enable MAVLink 2 Message Signing (built in)

The Conduit has HMAC-SHA256 MAVLink 2 signing built in. When enabled, it rejects any command that is not correctly signed — injected commands are dropped before reaching the flight controller. MAVLink 1 traffic from the FC is upgraded to signed MAVLink 2 automatically.

Enable from the dashboard:

1. Settings → Secure MAVLink → turn on Enable MAVLink Signing
2. GENERATE KEY (or paste an existing 64-character key and SAVE & PUSH) — the key is pushed to the device over the air
3. Copy the same key into your GCS:
   • QGroundControl — Application Settings → MAVLink → Signing Key
   • Mission Planner — Config → MAVLink → Signing

A GCS connected locally over Bluetooth (Section 12) is trusted by default — no keys needed for local flying. Signing protects the internet-facing relay path.

12. Connecting Your Ground Control Station (Mission Planner / QGroundControl)

Two ways to connect a GCS to the Conduit: over cellular or over Bluetooth.

Cellular (LTE)

When you log into your SkyRelay account you will find your personal UDP connection information that you can use with your favorite GCS software. To retrieve the information:

• Log into your Conduit dashboard
• Click Monitor
• Copy the Host and Port from the GCS card
• Additionally, the same information is listed in Settings under GCS Connection

Bluetooth (Local)

The Conduit accepts a direct Bluetooth connection from QGroundControl or Mission Planner on a phone, tablet, or laptop. This local MAVLink link runs alongside the cellular relay and works with no cellular coverage at all — a remote operator can watch over the cellular relay while you fly locally.

Connecting:

1. Power on the Conduit and wait for the boot beep (HI) — Bluetooth is available before the cellular modem starts
2. On your phone/laptop, pair with conduit-<device ID>
3. Add the connection in your GCS:
   • QGroundControl — Application Settings → Comm Links → Add → Bluetooth, select the Conduit
   • Mission Planner — select the Conduit's Bluetooth COM port and click Connect

Notes:

• The flight controller stays wired to the Conduit over UART — no Bluetooth hardware needed on the FC
• One Bluetooth GCS at a time; the cellular relay continues in parallel
• Local Bluetooth connections are trusted by default — no signing keys needed locally
• Cloud telemetry and the dashboard still require the cellular link

13. Cellular Data Plan and Usage Limits

Reducing Data Usage

• GCS Relay (Settings) — off = no MAVLink over cellular at all; cloud telemetry and flight logs continue
• Data Saver (Settings) — batches MAVLink into fewer, fuller packets; significant data reduction for a small added latency

Your GCS shows the Conduit's LTE signal strength as a radio signal bar while connected over the cellular relay.

14. Physical Mounting & Specifications

Mounting

Mount the Conduit away from your drone GPS and antennas to reduce interference. LilyGo uses Bluetooth, Wi-Fi and LTE bands which generally do not overlap with radio control frequencies. Given the wide range of radio communications and spectrums, ensure that the Conduit is placed away from critical navigational components.

Attach the Conduit firmly to your asset to minimize vibrations. You can add double-sided foam to attach it to the frame and use battery straps to further secure the unit.

Specifications

See Section 16 for exact dimensions and weight.

15. Troubleshooting

16. Specifications

Hardware

Electrical

Communication

Certifications

Changelog

v1.6.0

• Data Saver — Settings toggle that batches MAVLink into fewer packets to cut cellular data
• LTE signal bar in your GCS — cellular signal strength reported into the MAVLink stream
• Device health on the dashboard — processor load and memory alongside Link RTT

v1.5.0

• Local Bluetooth GCS link — direct QGC / Mission Planner connection over Bluetooth, alongside the cellular relay (Section 12). Replaces the old mode where the Conduit connected out to an FC's Bluetooth adapter.

v1.4.x

• Built-in MAVLink 2 signing managed from the dashboard (Section 11)
• Richer telemetry — speed, climb, throttle, home distance, HDOP
• Flight modes by name including Smart RTL, across ArduPilot vehicle types
• Morse buzzer sequences — HI on boot, K on cloud connect, OTA tones
• Lost / Stolen QR contact reveal (Section 8)

v1.6.1

• Automatic SIM-swap recognition — install a different SIM card and power-cycle the Conduit; it re-registers itself automatically, no manual reset needed

v1.6.4

• Bug fix — resolved a server-side configuration issue that could cause a device to repeatedly drop and reconnect shortly after coming online