SkyRelay Conduit

1. Overview

Conduit is firmware that connects your drone’s flight controller (FC) to SkyRelay and your ground control station (GCS) over a cellular network. It runs on hardware installed on the drone, including LilyGo boards and Raspberry Pi.

Compatible flight controllers include ArduPilot (Copter, Plane, Rover) and PX4 with a MAVLink telemetry port. Feature coverage varies by autopilot, software version, and vehicle type. Keep the flight controller at its default system ID of 1 (SYSID_THISMAV on ArduPilot, MAV_SYS_ID on PX4); commands sent from your SkyRelay account are addressed to system 1.

2. Hardware Setup

K01 kits arrive assembled. Continue with Installation. For a self-assembled device, follow the instructions for your board below.

LilyGo T-SIM7600NA

K01 — Assembled Kit

K02 — Assembly Kit

You need a LilyGo T-SIM7600NA board, an 18650 battery, a case, and the following kit components:

1. Attach the LTE and GPS antennas.
2. Insert the Hologram SIM in the nano-SIM slot on the underside of the board.
3. Solder the buzzer harness and UART breakout board connections shown in Figure 3 and the table below.
4. Fit the 18650 battery and case.
5. Install Conduit over USB, selecting T-SIM7600NA.

Flight Controller and Buzzer Wiring

Power

USB-C or the FC cable’s 5V supply powers the board and charges the 18650 battery. The battery supplies backup power when external power is lost.

Conduit reports battery voltage, estimated charge level, and external power status.

LilyGo T-PCIE 16M

You need a T-PCIE 16M board (revision V1.2 or later — V1.1 boards use a different power chip and are not supported), a SIM7600NA modem card, LTE and GPS antennas, a Hologram nano-SIM, an 18650 battery, a buzzer with harness, an FC cable, and a case.

1. Install the modem card in the mini-PCIe socket. Connect the LTE antenna to MAIN and the GPS antenna to GPS/GNSS.
2. Set DIP switches 1 and 2 ON and 4 OFF.
3. Insert the SIM.
4. Solder the FC cable to the header pins using Figure 4 and the table below.
5. Connect the buzzer: I/O → GPIO 23 (right header, 7th from top), V → 3.3V, G → GND.
6. Fit the 18650 battery and case.
7. Install Conduit over USB, selecting T-PCIE 16M.

Flight Controller Wiring

Header positions are counted from the top with the USB-C port at the bottom.

Power and Buttons

External power runs the board and, when the supply can spare the current, charges the 18650 battery. The battery supplies backup power when external power is lost. If the FC’s 5V supply is limited, the battery may help carry the board during heavy cellular activity instead of charging.

Conduit reports battery voltage, estimated charge level, and external power status.

Auto power-off. If the flight controller has been connected and then stops sending data for 5 minutes, the T-PCIE turns itself off completely to save the battery. Reconnecting the flight controller within that time cancels it. Hold PWR for 1 second to turn the board back on.

• PWR — hold for 1 second to power on.
• EN — press to reset.

3. Installation

1. Activate the Device

Activate your device through your SkyRelay account. K01 kits include a QR code on the case and activation card.

2. Connect the Flight Controller

Use the wiring table for your board: T-SIM7600NA or T-PCIE 16M.

FC Cable Connector

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 5:

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

3. Configure the Telemetry Port

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

4. Mount the Device

Secure the device to the airframe with foam padding and straps. Keep it clear of the aircraft’s GPS receiver and antennas.

5. Power On

Turn on the device. The buzzer plays HI at startup and K when connected to the cloud. See Buzzer Codes for the tone patterns.

6. Check the Connection

Open your SkyRelay account and confirm that the device is online and receiving flight-controller data. Check the reported position and battery level before use.

4. Connect Your GCS

Cellular (LTE)

Your GCS reaches Conduit through the SkyRelay private network, not the open internet. Enroll each computer, phone, or tablet that runs your GCS once (see Enroll Your Device), then:

1. Make sure the device is connected to the private network (the Tailscale app shows Connected).
2. In your GCS, add a UDP connection using the host and port shown for your Conduit in your SkyRelay account.

Enroll Your Device

Each device that runs your GCS needs its own enrollment — signing in to SkyRelay is not enough. You also need access to the Conduit: owners have it; other people must be approved on the Private Network page.

1. Install the Tailscale app on the device from tailscale.com/download.
2. In your SkyRelay account, open Private Network and click Enroll GCS.
3. Enter a name for the device (for example, “Flight laptop”) and choose its type.
4. Choose an enrollment path:
   • Desktop command (Windows, Mac, Linux) — click Create enrollment. SkyRelay shows a single-use command. Copy it and run it on that device in a terminal (Command Prompt or PowerShell on Windows; the Mac and Linux command starts with sudo). Then click Check connection on the device’s card.
   • Tailscale app / Auth ID (iPhone, iPad, Android, or any desktop) — in the Tailscale app, choose an alternate (custom) coordination server and enter the SkyRelay server address shown in the dialog. Begin signing in, copy the Auth ID that Tailscale shows, paste it into SkyRelay, and click Confirm and enroll.
5. The device appears under Enrolled GCS clients.

Check that your device is connected

• On the Private Network page, the device shows Online.
• On the device, the Tailscale app shows Connected, or run tailscale status in a terminal.
• To check the private-network tunnel, run tailscale ping <host> with the host shown for your Conduit. A pong reply means the tunnel to SkyRelay works. It does not confirm that your Conduit is online or that you have access to it — telemetry arriving in your GCS is the final check.

Bluetooth Maintenance

Use a local Bluetooth Classic (SPP) connection for maintenance with QGroundControl or Mission Planner. Conduit does not appear in BLE scanner apps.

Bluetooth is for maintenance on the ground only. Conduit disconnects the Bluetooth link when the aircraft arms and refuses new connections until it is disarmed. Bluetooth GCS access can be turned off in Settings → GCS Relay.

1. After powering on, wait up to 30 seconds (longer if there is no cellular signal) for Conduit to appear as conduit-NNNN, where NNNN is the device ID.
2. In your phone or laptop’s Bluetooth settings, pair with conduit-NNNN.
3. Select the Bluetooth Classic connection or Bluetooth serial port in your GCS.

Reduce Cellular Data Usage

• GCS Relay — turn off cellular MAVLink forwarding when unused; cloud telemetry continues.
• Data Saver — enable packet batching to reduce cellular data usage.

Network RTK

With Network RTK configured in your SkyRelay account, Conduit sends positioning corrections to the flight controller over MAVLink. An RTK-capable GPS receiver is required.

5. Buzzer and Recovery

Signal-loss Alert

Enable Alert on Signal Loss in Settings to sound SOS when the cloud connection is lost. The setting is saved across restarts. The alert stops when the connection returns.

Locate a Lost Drone

Activate the lost-drone buzzer from your SkyRelay account to help locate the aircraft by sound. A cellular connection is required to activate it.

FC/ESC Buzzer

During SOS, and when you press TEST BUZZER, Conduit also sends a locator tone to a connected flight controller while the aircraft is disarmed. This follows the same Buzzer setting and works even with no buzzer fitted to the Conduit. For ArduPilot with DShot ESCs, include DShot in NTF_BUZZ_TYPES to sound the tone through the motors.

QR Recovery — K01 Kit

A finder can scan the QR code on the K01 case to initiate contact with the operator.

Buzzer Codes

6. 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)

7. Firmware Updates

Over-the-Air (OTA)

Conduit supports firmware updates over LTE. Start an OTA update from your SkyRelay account; the device downloads the firmware and reboots after installation.

WebSerial (USB)

Install firmware from a computer using a USB-C cable.

1. Go to www.skyrelay.us/conduit/firmware.html in Chrome or Edge
2. Select your board — T-SIM7600NA or T-PCIE 16M
3. Connect the Conduit via USB-C
4. Click Flash and select the device's serial port when prompted
5. Device reboots with the new firmware

The board you select also decides which updates this Conduit accepts later. The browser can’t detect which board is connected; if the wrong build is flashed the device may not start — flash again with the right selection.

CLI (esptool)

1. Download the latest .bin file for your board 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

This replaces the application only. To set up a new board, switch board types, or recover a Conduit that won’t start, use WebSerial — it also writes the bootloader and partition layout for the board you select.

8. Troubleshooting

9. Specifications

Hardware — LilyGo T-SIM7600NA (K01 assembled unit)

Hardware — LilyGo T-PCIE 16M

Communication

10. FCC Compliance