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Overview of Prototype V1

Overview of Prototype V2

How it's done

In the development of this project, STM32 CubeMX and CubeIDE were used to configure and generate the HAL (hardware-abstraction-layer). Some says I'm cheating and using a code generator. I don't disagree XD.

To edit/compile/flash the code you only need to install CubeIDE. Although feel free to use any tools you like. You can download CubeIDE here: https://www.st.com/en/development-tools/stm32cubeide.html

The intricacies of animating 64 LEDs with Timer16

The clock is set to 8Mhz and the timer16 counter is set to 1000 (see "tim.c"). Thus 8Mhz/1000=8Khz. The timer runs at 8khz. It updates a new LED 8000 cycles per second.

Analogy

Imagine there is a cursor that is moving left to right, top to bottom. Every cycle, the cursor moves to the next LED, reads the buffer and decides if the LED should be on/off. In other words, it takes 64 cycles to update the full screen since there is 64 LEDs. Consequently, it takes 8000Hz/64LEDs = 125ms to update the full screen.

Where is the timer handler?

The timer handler function "HAL_TIM_PeriodElapsedCallback()" is called in the file "stm32f0xx_it.c". At that location the "screen_interruptUpdate()" function is called to update the next LED.

About LED Matrix

The chip we are using is the STM32F0. The datasheet indicates that the maximum current through a whole GPIO PORT is 30mA. The LEDs are running at 20mA with the chosen current limit resistor. Therefore, the code is set to only turn on 1 single LED at a time in order to satisfy that requirement. Since the whole screen is updated every 125ms, there is enough persistence of vision to produce a consistent animation.

The low-level function which controls the individual LEDs is located in "ledHandler.c". The function "matrix_setLed_on()" is used to enable an LED. It can be seen that at the beginning of it, it calls "matrix_setLed_allOff()" to disable any previous LEDs and ensure the PORT never source more than 30mA.

About screenBuffer.c

The screenBuffer is how you interact with the LED matrix. There is 1 main fundamental fonction you need:

  • screen_set_bit(row, column, state)

This is function set the state of each LEDs in the 8x8 matrix. It's either 1 (on) or 0 (off).

Additionally, there are helper functions to make animating easier:

  • screen_get_bit()
  • screen_fill()
  • screen_clear()

How to Flash

Things you need:

Instruction

  • Connect the ST-Link SWD header to the PCB's programming port
  • Compile the code in STM CubeIDE: "Project"->"Build All"
  • Connect your Nucleo board to your computer
  • Configure the debugger as follows: "Run" -> "Debug Configurations"
  • Flash the firmware: "Run" -> "Run"
  • You will see this in the logs
  • Memory Programming ...
Opening and parsing file: ST-LINK_GDB_server_a15460.srec
  File          : ST-LINK_GDB_server_a15460.srec
  Size          : 21.34 KB 
  Address       : 0x08000000 
Erasing memory corresponding to segment 0:
Erasing internal memory sectors [0 21]
Download in Progress:
File download complete
Time elapsed during download operation: 00:00:01.454
Verifying ...
Download verified successfully 
Shutting down...
Exit. 
  • You might have to power cycle the PCB to get the firmware started the first time
  • Congrats, you have flashed the addon. Happy coding.