SSD1306 OLED Servo Control with STM32 Blue Pill

This project demonstrates how to control a servo motor using an IBT_2 (BTS7960) motor driver, an STM32 Blue Pill, and a 128x64 SSD1306 OLED display. The user can control the motor's speed and direction using four push buttons, with real-time feedback on the OLED screen.

Features

• Motor Control: Adjust speed and direction of a servo motor.
• OLED Display: A 128x64 SSD1306 OLED display shows the current speed, direction, and motor state (ON/OFF).
• User Interface: A simple and intuitive interface with four buttons for control (Up, Down, OK, Cancel).
• Two-Color Display Optimization: The UI is designed for two-color (Yellow and Blue) OLED displays, with a static header in the yellow section and dynamic values in the blue section.

Hardware Required

• STM32F103C8T6 "Blue Pill" development board
• 128x64 SSD1306 OLED display (I2C) with 4 push buttons (up, down, OK, Back)
• IBT_2 (dual BTS7960) motor driver
• Servo motor e.g.: RS-550 or R-775
• External power supply for the motor 12-24V/5A
• Breadboard and jumper wires

Wiring

Connect the components to the Blue Pill as described below.

OLED Display (I2C)

OLED Display Pin	Blue Pill Pin
VCC	3.3V
GND	GND
SCL	PB6
SDA	PB7

Control Buttons

The buttons are connected to GPIO pins using the internal pull-up resistors. The other terminal of each button should be connected to GND.

Button Function	Blue Pill Pin
Up	PA0
Down	PA1
OK	PA2
Cancel	PA3

IBT_2 Motor Driver

The IBT_2 module requires its own power supply for the motor.

IBT_2 Pin	Blue Pill Pin	Description
VCC	5V	Logic Power
GND	GND	Logic Ground
R_EN	3.3V	Right Enable (connect to 3.3V)
L_EN	3.3V	Left Enable (connect to 3.3V)
RPWM	PB0	Right PWM Signal (Forward)
LPWM	PB1	Left PWM Signal (Reverse)

DAPLink UART

For debugging and logging, you can connect the DAPLink's virtual COM port to the Blue Pill's UART1.

DAPLink Pin	Blue Pill Pin	Description
RXD	PA9 (TX1)	Connect to TX
TXD	PA10 (RX1)	Connect to RX
GND	GND	Common Ground

IBT_2 Power Connections:

IBT_2 Terminal	Connection
B+	Positive of Motor Power Supply
B-	Negative of Motor Power Supply
M+	Positive of Servo Motor
M-	Negative of Servo Motor

Dependencies

This sketch requires the following Arduino libraries:

• Wire
• Adafruit_GFX
• Adafruit_SSD1306
• Adafruit_BusIO (A dependency for the Adafruit libraries)

Getting Started

Prerequisites

• Arduino CLI
• STMicroelectronics STM32 core

Installation

1. Install arduino-cli: Follow the official instructions at arduino.github.io/arduino-cli/installation/.

2. Initialize and Configure arduino-cli:

   • Create a default configuration file:

     arduino-cli config init
     

   • Add the STMicroelectronics board manager URL:

     arduino-cli config add board_manager.additional_urls https://github.com/stm32duino/BoardManagerFiles/raw/main/package_stmicroelectronics_index.json
     

   • Update the local core index:

     arduino-cli core update-index
     

   • Install the STM32 core:

     arduino-cli core install STMicroelectronics:stm32
     

3. Install Required Libraries:

   arduino-cli lib install "Adafruit SSD1306" "Adafruit GFX Library" "Adafruit BusIO"
   

Board Setup

In Arduino IDE → Tools, set:

Board → STM32 MCU based boards → Generic STM32F1 series

Board part number → BluePill F103CB (or C8 with 128K)

Upload Method → OpenOCD DAPLink (SWD)

Compilation

1. Prepare Your Sketch Directory: Ensure your sketch file is named SSD1306_sketch.ino and is located in a folder with the same name. For example: /path/to/your/project/SSD1306_sketch/SSD1306_sketch.ino

2. Compile the Sketch: Compile the sketch for the Blue Pill (STM32F103CB or C8 with 128k), specifying the OpenOCD upload method.

   arduino-cli compile --fqbn STMicroelectronics:stm32:GenF1:pnum=BLUEPILL_F103CB,upload_method=OpenOCDDapLink /path/to/your/project/SSD1306_sketch
   

   The binary files will be generated in a temporary build directory. To find the path to the binary, you can run the compile command with the --verbose flag.

Upload to the Board

The compiled sketch can be uploaded to the Blue Pill using openocd. The exact command may vary depending on your setup.

First, you need to find the path to your compiled .elf file. You can find this in the output of the arduino-cli compile command. It will be in a temporary directory ~/.cache/arduino/sketches.

Then, find the openocd e.g.: ~/.arduino15/packages/STMicroelectronics/tools/xpack-openocd/0.12.0-6/bin/openocd or install a distro specific version e.g.: sudo apt install openocd. Example of the path to the compiled sketch: /home/martin/.cache/arduino/sketches/96DBB1C909C240C2F96DCDD5DDFB9A12/SSD1306_sketch.ino.elf

Here is an example command to upload the sketch using DAPLink:

/path/to/your/openocd -d2 -f interface/cmsis-dap.cfg -f target/stm32f1x.cfg -c "program {/path/to/your/sketch.ino.elf} verify reset exit"

🐞 Hardware Debugging with DAPLink (CMSIS-DAP) on Blue Pill

This section describes how to enable hardware debugging for the STM32F103 "Blue Pill" board using a DAPLink / CMSIS-DAP debugger in Arduino IDE 2.
By default, the STM32 Arduino core loads the wrong OpenOCD configuration (dapdirect_swd, meant for ST-Link).

Until the (bug)[https://github.com/stm32duino/Arduino_Core_STM32/issues/2807] is not fixed, follow these steps to fix it:

🧭 1. Locate STM32 Core Folder (Linux)

Open a terminal and navigate to your STM32 Arduino core installation:

cd ~/.arduino15/packages/STMicroelectronics/hardware/stm32/2.11.0/

Adjust the version number if different (check in Arduino IDE → Tools → Board → Boards Manager).

🧰 2. Create or Edit platform.local.txt

Create (or edit) a local override file:

nano platform.local.txt

Paste the following lines:

debug.server.openocd.scripts.0=interface/cmsis-dap.cfg
debug.server.openocd.scripts.1={runtime.platform.path}/debugger/select_swd.cfg

Save and close (Ctrl + O, Enter, Ctrl + X).

These lines tell OpenOCD to:

Use the CMSIS-DAP interface (interface/cmsis-dap.cfg)

Use standard SWD transport (select_swd.cfg) instead of dapdirect_swd

🔁 3. Restart Arduino IDE

Completely close and reopen Arduino IDE 2 to apply the new settings. ⚙️ 4. Configure the IDE

In Arduino IDE → Tools, set:

Debug symbols and core logs → Core Logs and Symbols Enabled (-g)

Optimize → Debug (-Og)

Then click the 🐞 Debug icon and press Start Debugging.