Introduction

This is a minimalistic implementation of a brushless DC motor driver on STM8 microcontrollers. It is presently limited to the small (1100kv) brushless outrunners such as seen on cheap drones and RC planes.

The software drives the motor by applying the 6-step (trapezoidal) drive sequence. Motor synchronization is to be accomplished by using the motor back-EMF waveform sampled by the ADC (analog digital converter) input to the STM8.

Obtaining and installing development environment

Presently the de-facto toolchain is ST Visual Develop with COSMIC C compiler - these tools have free licenses, but are available for Windows OS only.

sdcc (available for multiple OS) may be supported at some point and eventually transition to patched for use with SDCC as that one has all C files split into one function per file (SDCC linker unable to perform dead code elimination?)

Download IDE and compiler toolchain:

• Download STVD STVD
• Install STVD - run the downloaded STVD installer 'sttoolset_pack42.exe'
• Download COSMIC STM8 C Compiler
• Install COSMIC STM8 C Compiler and restart machine (to update PATH etc.)
• Follow instructions to register for the free license for COSMIC STM8 C Compiler
• Save COSMIC license file to e.g : C:\Program Files (x86)\COSMIC\FSE_Compilers\CXSTM8\License_

Working with stm8_mcp project source code

Installing STSW-STM8069 STM8S/A Standard peripheral library

• Navigate browser to Standard peripheral library homepage - application note STSW-STM8069
• Register with ST if required to do so.
• Get an email from ST with link to download en.stsw-stm8069.zip (SPL Version 2.3.1)
• unzip en.stsw-stm8069.zip into your project directory.

Cloning source code from github:

• cd Your_project_directory/STM8S_StdPeriph_Lib/Project/
• git clone https://github.com/gneidermeier/stm8_mcp.git (master branch)
• Open project in STVD, 'File | Open Workspace' .. browse to STM8S_StdPeriph_Lib\Project\stm8_mcp\STVD\Cosmic\STVD_workspace.stw

Select the active project:

• In the STVD_workspace window, right click e.g. stm8s105_devblk

Selecting the active project sets the platform by inserting the compiler define '-dS105_DEV' into the compile command.

• Compile and link project (F7)
• Run code in debugger (Alt-D D)

Note on installation/configuration of SPL:

The stm8_mcp project was copied from the SPL template V2.3.0. (STM8S_StdPeriph_Lib/Project/STM8S_StdPeriph_Template).

As in the template project, the location of the SPL source files is set in the stm_mcp project as a relative path. The SPL library files are kept external to the stm_mcp project and not distributed with it, thus the requirement to download it separately.

If creating a new project and not a copy of the template, be sure to setup the toolchain in STVD:

• Select the toolchain e.g. 'STM8 Cosmic' and set Toolchain root e.g.: C:\Program Files (x86)\COSMIC\FSE_Compilers\CXSTM8
• In project settings, set the MCU Selection e.g. 'STM8S105K6' (issues compiler directive -dSTM8S105)

Running the controller with a motor

The critical component of the hardware is the 3-phase driver circuit. The 3-phase driver circuit is implemented in large part by the [IR2104 half-bridge IC] (https://www.infineon.com/dgdl/Infineon-IR2104-DS-v01_00-EN.pdf?fileId=5546d462533600a4015355c7c1c31671). Most variations of the this kind of circuit use an [N channel MOSFET] (https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d) for both the high-side as well as low-side of the half-bridge. The IR2104 incorporates a built-in charge pump for driving the high-side (Vgs of HS going to be significantly higher than Vbat).

Reference project implements the controller with an Arduino Uno, which has the additional capability of the input comparator. This provides a means for detecting zero-crossing point and thus direct measurement of motor timing.

Connecting a motor can cause the potential for more dramatic failure scenario so do it at your own risk to your dev board and equipment!

The following equipment is suggested:

• stm8s105 development board (stm8s105c Discovery or stm8s105k "Black" board)
• 1100kv brushless motor
• Benchtop power supply (alternatively, 11.1v 3s pack)
• FTDI cable (for remote user interface)

• A 3-phase driver circuit e.g. the hardware schematic (in Kikad) for the stm8s105k configuration can be found in this repositiory

  Connect the FTDI cable (orange to STM8 Rx, yellow to STM8 Tx) Power the STM8 dev board (USB micro connector or 5 volt power source connected to STM8 5v pin).

  Power the bench supply (keep eye on current meter)!

  Use remote serial terminal (via e.g. PuTTY, Tera Term, Minicom) to interact with motor software.

  • Pressing comma or period keys (< and > signs) starts the motor if not running.
  • Once motor is running, pressing comma or period keys (< and > signs) increases/decreases the PWM duty-cycle applied to the motor phase
  • Space bar stops the motor.

  Motor operation is limited to about 50% duty-cycle.

Build Documentation

The project documentation is generated from Doxygenized comments in the code and supplemented by diagrams generated from markup by PlantUML. GitHub pages is set to serve from a gh-pages branch of the project repo - Documentation link.

GitHub now provides option for Simpler GitHub Pages publishing which could be considered.

Prerequisites:

• [Doxygen] {https://www.doxygen.nl/download.html} - available for Windows as self-installing archive and included GUI, or as 32-bit or 64-bit standalone binary zip if preferred.
• PlantUML is distributed as a single jar
• (java archive) and requires a functional java (installation of which not covered here, sorry!)
• Set PLANTUML_JAR_PATH environment variable to location of plantuml.jar Windows 10 and Windows 8 In Search, search for and then select: System (Control Panel) Click the Advanced system settings link. Click Environment Variables. In the section System Variables, add the new system variable by selecting New

To build the documentation:

1. Open the Command Prompt (or alternatively, Power Shell) in Windows and execute the command cd <project_root> to navigate into the project root directory.
2. In a Windows Command Prompt run doxygen from the root of the project root directory and capture the output to a text file: doxygen docs\config\doxyfile.cfg 2>&1 > doxygen.log

The documentation is generated under the <project_root>/build directory. Open <project_root>/build/html/index.html to view the HTML documentation.

Update documentation on GitHub pages

In a separate project directory, create a clone of the project repo in which to checkout the gh-pages https://github.com/gneidermeier/stm8_mcp/tree/gh-pages.

In the gh-pages clone-repo, create an orphan branch 'gh-pages' - (I needed [help with this] https://stackoverflow.com/questions/48235671/deploy-project-to-gh-pages-from-a-git-clone).

Replace all of the contents in the docs/ directory of the gh-pages branch with the contents of <project_root>/build/html in the build branch. Execute the commands shown below in an appropriate shell environment (e.g. Linux, Git Bash or Cygwin) to deploy the docs in gh-pages:

cd /path/to/my/clone_clone_of_gh-pages
git checkout --orphan gh-pages
git rm -rf .
rm '.gitignore'
echo "#Project gh-pages site" > README.md
cp -r `<project_root>/build/html/* docs/
git add docs/
git commit -a -m "Initial Commit"
git push -u origin gh-pages

If there is any conflicts with the gh-pages branch, it is easy to delete a branch (e.g. on github web) and the commands above will then work to regenerate the branch.