Open-Source RC Transmitter and Receiver System with stm32

Overview

The XRC PRO is an advanced, open-source RC transmitter and receiver system designed to offer professional-level performance in a compact and customizable package. Built around the STM32F103C8T6 microcontroller and the NRF24L01 wireless transceiver module, the XRC PRO provides precise, real-time control for various RC applications like drones, cars, and boats. With a compact design, robust functionality, and user-friendly interface, the XRC PRO is an ideal tool for both hobbyists and professionals.

Key Features:

• OLED Display: Shows real-time signal strength, settings, battery percentage, and control data for easy monitoring.
• Trim Buttons & Rotary Encoder: Provides fine-tuned control and simple menu navigation, enhancing usability.
• Multi-Menus: Features an intuitive menu system for adjusting channel settings, polarity, and output modes.
• PPM & SBUS Outputs: Offers versatile output options, supporting a range of RC receivers for greater functionality.
• NRF24L01 Power Control: Includes adjustable signal strength settings, allowing for both short- and long-range control.
• Stick Calibration: Enables real-time stick calibration with visual feedback on the OLED display for precise adjustments.
• Compact Receivers: Offers two efficient receiver options for 8-channel PWM+PPM and PPM+SBUS outputs, designed for optimal performance.
• Throttle Mode: Allows selection between left or right throttle hand mode to suit user preferences.
• PC Simulator Compatibility: Supports computer-based simulators through PPM output, with an option to toggle PPM output on or off.
• Express ELRS Integration: Compatible with ELRS modules via PPM output when used with an ELRS adapter.
• Buzzer On/Off Mode: Enables users to easily toggle the buzzer for audio feedback during operation.
• Adjustable Setting Unit: Allows customization of measurement units (e.g., degrees, percentages) based on user preference.
• Battery Voltage Calibration: Calibrate battery voltage display for accurate percentage readings, ensuring reliable battery monitoring.
• Reset to Default Settings: Provides an option to restore all settings to default quickly for easy setup and troubleshooting.

Tech Specs

Microcontroller: STM32F103C8T6 ARM® Cortex®-M3

• ARM® Cortex®-M3 core up to 72 MHz
• 20KB onboard SRAM
• 64KB Flash memory

Wireless Module: NRF24L01 GT24 Mini

• Operates on 2.4 GHz ISM band
• High data rate up to 2 Mbps
• Supports multiple data pipes for communication

Display: 0.96" OLED

• Displays signal strength, battery percentage, and control data

Power: AMS117 3.3V Regulator

• Input voltage range from 7.4V to 12V (supports 2S to 3S LiPo batteries)

Weight: 200g (excluding battery)

Dimensions: 160 mm x 120 mm x 40 mm (excluding antenna)

Enclosure: DJI Phantom 2 Remote (customizable based on user preference; Arduino joysticks can be used as an alternative)

Transmitter PCBs

The Transmitter PCB is built around the STM32F103C8T6, NRF24L01 module, OLED display, and various input buttons (trim, menu, encoder). The schematic includes connections for power management (5v to 3.3v), data lines for the OLED, and button inputs for settings navigation etc.

Schematic and PCB Layout

Menu-Keys

Schematic and PCB Layout

Rotary Encoder+Switch

Schematic and PCB Layout

Trim Buttons

Type C Jack

Schematic and PCB Layout

Receciver PCBs

8-channel PWM+PPM Receiver PCB

The 8-channel receiver supports both PWM and PPM outputs. It is based on the NRF24L01 and STM32F103C8T6 for signal decoding and generation.

Schematic and PCB Layout

PPM+SBUS Receiver PCB

The PPM+SBUS receiver is another compact design focused on supporting more advanced control protocols. It also features the STM32F103C8T6 for signal processing and output.

Schematic and PCB Layout

Visual and Physical Connections

I’ve designed a detailed, color-coded connection schematic for all inputs and outputs, making it easy for anyone to assemble the XRC PRO transmitter and receivers. Additionally, I’ve included high-quality these images in PDF format, which you can download below.

Transmitter

Receiver(PWM+PPM)

Receiver(PPM+SBUS)

Firmware Overview

The XRC PRO's firmware is developed in Keil uVision using the CMSIS framework for STM32. It is fully open-source, with modular code to allow easy customization and extension of the system's capabilities. The main focus of the firmware is on handling communication between the transmitter and receivers, as well as managing the various control inputs.

Here the whole files in KeiluVision:

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