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QLiteArmer — HD Armer and Full OSD with Dual‑Core RP2040 Telemetry MSP DisplayPort Processor

QLiteArmer Custom PCB — Fully Assembled

QLiteArmer is a dual‑core RP2040‑based telemetry OSD and HD arming system designed for FPV pilots, RC FPV vehicles, RC builders, and embedded developers.
It provides:

  • Full Betaflight‑style OSD for DJI O3/O4 and Walksnail Avatar HD
  • GPS + barometer telemetry processing
  • CRSF/ELRS channel breakout
  • PWM‑based arming (Channel 5)
  • 8‑channel servo expansion
  • Deterministic, non‑blocking architecture

QLiteArmer is an OSD and arming module — arming is controlled by RC PWM Channel 5.

Get the QLiteArmer PCB Short Kit Here

QLiteArmer Custom PCB — Fully Assembled

✨ Features

Full OSD Engine (MSP DisplayPort)

QLiteArmer includes a complete Betaflight‑compatible OSD renderer supporting:

  • Satellite count
  • Pack voltage
  • Cell voltage
  • Vertical speed
  • RC link quality (ELRS LQ)
  • Distance from home
  • Altitude
  • Ground speed
  • Total trip distance
  • Latitude / longitude
  • Home arrow (16‑direction)
  • Ground radar of home
  • Crosshair
  • Flight timer
  • Throttle value
  • Compass heading

Compatible with:

  • DJI O3 / O4 Air Unit
  • Walksnail Avatar HD (Goggles X / VTX)

Uses Betaflight character mappings and custom glyphs for home arrow rendering.

🖼 Betaflight-Compatible Character Map (Walksnail Avatar HD)

This project includes a full custom character map matching Betaflight’s DisplayPort glyph layout, adapted for Walksnail Avatar HD.

Betaflight-Compatible Character Map (Walksnail Avatar HD)

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🎮 PWM‑Based Arming (Channel 5)

Arming is now 100% PWM‑based:

  • Uses RC Channel 5 (default)
  • Arms when PWM > threshold (default: 1700 µs)
  • Disarms when PWM < threshold

This ensures predictable, pilot‑controlled arming behavior.

🛰 Telemetry System

GPS Telemetry

  • Autodetects baud rate (9600, 38400, 57600, 115200)
  • Home position lock
  • Distance from home
  • Bearing to home
  • Ground radar showing home
  • Ground speed
  • Latitude / longitude
  • Total trip distance
  • GPS fix + satellite count

Barometer (BMP280)

  • Altitude (cm)
  • Vertical speed (cm/s)

Battery Monitoring

  • VBAT via ADC
  • Configurable voltage divider
  • Pack voltage displayed in OSD
  • Per cell voltage

Units

  • Metric or Imperial (configurable)

🧩 Servo Expansion (8‑Channel PWM Output)

QLiteArmer includes a hardware‑accurate servo expander:

  • 8 PWM outputs
  • Per‑channel min/max mapping
  • Per‑channel failsafe values
  • Frequency‑matched output
  • CRSF/ELRS channel passthrough
  • Ultra‑stable RP2040 hardware PWM

Define individual channel range and failsafe in the config.h file:

static const ChannelMap CH_MAP[8] = {
    {988, 2012, 1500},   // CH1
    {988, 2012, 1500},   // CH2
    {988, 2012, 1000},   // CH3 (Throttle failsafe = 1000)
    {988, 2012, 1500},   // CH4 
    {988, 2012, 1500},   // CH5
    {500, 2500, 1500},   // CH6 (expanded range)
    {988, 2012, 1500},   // CH7
    {988, 2012, 1500}    // CH8
};

⚙ Pin Map

Function Pin(s) Notes
CRSF / ELRS UART GP8 (TX), GP9 (RX) Primary RC link
MSP UART (VTX) GP0 (TX), GP1 (RX) DJI / Walksnail
I²C (BMP280) GP4 (SDA), GP5 (SCL) Barometer
VBAT ADC GP26 Voltage divider
PWM CH1–CH8 13, 12, 11, 10, 7, 6, 3, 2 Servo/motor outputs
RGB LED GP16 Onboard WS2812
GPS GP14 (TX), GP15 (RX) 4‑wire GPS

Software & Environment Setup

This project is built for the Raspberry Pi Pico / RP2040 / RP2350 architecture using the Arduino IDE. Follow the steps below to configure your development environment.

1. Install the Board Support Package (BSP)

You must use the Arduino Pico core maintained by Earle F. Philhower, III.

  1. Open the Arduino IDE.
  2. Navigate to File -> Preferences.
  3. Locate the Additional Boards Manager URLs field and paste the following URL: 
    https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json
  4. Click OK.
  5. Go to Tools -> Board -> Boards Manager...
  6. Search for Pico or Philhower and install Raspberry Pi Pico/RP2040/RP2350 by Earle F. Philhower, III.
  7. Once installed, go to Tools -> Board -> Raspberry Pi Pico/RP2040 and select Waveshare RP2040 Zero.

2. Install Required Libraries

Open the Arduino Library Manager (Tools -> Manage Libraries... or press Ctrl+Shift+I / Cmd+Shift+I) to search for and install:

  • Adafruit BMP280 Library (by Adafruit)
  • NeoPixelBus (by Makuna)

💡 Note: When installing the Adafruit BMP280 library, the IDE will ask to install required dependencies (like Adafruit BusIO and Adafruit Unified Sensor). Make sure to select Install All so everything compiles successfully.

🛠 Hardware Overview

QLiteArmer Custom PCB

QLiteArmer Custom PCB — Bare Board

QLiteArmer Custom PCB — Fully Assembled

QLiteArmer Custom PCB — Fully Assembled

🧰 Parts List (with Affiliate Links)

These are the recommended components for building a complete QLiteArmer module.
All links are affiliate links that help support the project at no additional cost.

Core Components

Power & Regulation

Passive Components

Headers & Connectors

Other Recommended Items

QLiteArmer OSD and HD Armer Detailed Build - RP2040 Zero FPV System

🚀 How It Works (High‑Level)

  1. Boot

    • System initializes dual‑core architecture
    • Blue LED indicates boot state

  2. Telemetry Acquisition

    • Core 1 handles GPS, barometer, battery, and OSD
    • Core 0 handles CRSF/ELRS and PWM output

  3. OSD Rendering

    • MSP DisplayPort frames generated in real time
    • Betaflight‑compatible glyphs
    • Home arrow computed from GPS bearing

  4. Arming

    • PWM Channel 5 controls arming
    • Red LED is holding and ready to arm
    • Green LED is armed with high power and recording
    • Amber LED no VTX detected

  5. Servo Expansion

    • CRSF channels mapped to PWM outputs
    • Failsafe values applied on link loss

🧠 System Architecture (Technical)

Core 0 (Time‑Critical)

  • CRSF/ELRS UART
  • PWM output generation
  • MSP heartbeat
  • Channel mapping
  • Failsafe handling

Core 1 (Telemetry + OSD)

  • MSP DisplayPort
  • GPS parsing
  • Barometer updates
  • Battery ADC
  • OSD composition
  • State machine
  • LED driver

SerialPIO Notes

  • SerialPIO is used for GPS
  • Requires careful initialization order
  • LED initialization must occur before SerialPIO

RP2040 vs RP2350

  • Both fully supported
  • LED color order differs between boards (Red and Green are swapted)
  • Auto‑detected via compile‑time selection

🔧 Configuration Reference

PWM Channel Mapping

Each channel has:

  • minUs
  • maxUs
  • failsafeUs

Example (from config.h):

static const ChannelMap CH_MAP[8] = {
    {988, 2012, 1500},   // CH1
    {988, 2012, 1500},   // CH2
    {988, 2012, 1000},   // CH3 (Throttle failsafe = 1000)
    {988, 2012, 1500},   // CH4 
    {988, 2012, 1500},   // CH5
    {500, 2500, 1500},   // CH6 (expanded range)
    {988, 2012, 1500},   // CH7
    {988, 2012, 1500}    // CH8
};

Arming Settings

  • PWM_ARM_CHANNEL = 4 (Channel 5 -- ZERO based mapping)
  • PWM_ARM_THRESHOLD = 1700
  • PWM_NO_SIGNAL_US = 900

Battery Divider

Default:

  • R1 = 30k
  • R2 = 7.5k

Telemetry Rates

  • Battery: 5 Hz
  • Altitude: 5 Hz

Units

  • Metric or Imperial

Timing

  • VTX detection timeout: 5 minutes
  • Heartbeat: 200 ms

LED

  • LED pin: GP16
  • LED count: 1
  • RP2040/RP2350 color order handled internally

Home Arrow Glyph Table

Rows 96–111
16 directions
22.5° increments
CCW orientation

🧪 Tested Hardware

  • RP2040‑Zero
  • RP2350-Zero
  • DJI O3 / O4 Air Unit
  • Walksnail Avatar HD
  • ELRS receivers
  • BMP280 barometer
  • Standard GPS modules

📄 License

MIT License — free to modify, extend, and integrate.

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Waveshare RP2040-Zero Pico based HD Armer and Servo Expander

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