STM32F1xx micro-controller C firmware template
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Firmware for the crown counter.



The crow counter just counts how many (per day and in total) caps (e.g. crown cork) have entered the basket.


An infra-red LED and photo-detector create a light barrier, broken when crossed by caps. An RTC keeps track of the days. 2 TM1637 7-segment displays show how many caps passed in total and today.


The underlying template also supports following board:

Which board is used is defined in the Makefile. This is required to map the user LED and button provided on the board


Connect the peripherals the following way:

  • IR LED: connected across 3.3V with potentiometer to adjust brightness
  • IR photo-detector: PB5
  • first TM1637 7-segment 4-digit display: CLK to PB6, DIO to PB7
  • second TM1637 7-segment 4-digit display: CLK to PB8, DIO to PB9
  • CR1220 to VBAT for the RTC


at first I use a KY-032 infrared sensor detects when a cap passes through the basket. this modules the infra-red LED (set to 38 kHz), and has an IR demodulator (at 38 kHz). I though this would be less noise prone, particularly from external IR sources. turns out it is a lot more. I tested will the cap reflecting the IR, but this is sometimes to short, and the demodulator might not detect it. I tested with the cap breaking the barrier, but the IR demodulator doesn't allow continuous IR burst detection and has a hard time detecting when it is broken and restarted. in the end, a simple LED on and photo-detector to create a barrier is super simple and efficient.



The source code uses the libopencm3 library. The projects is already a git submodules. It will be initialized when compiling the firmware. Alternatively you can run once: git submodule init and git submodule update.


To compile the firmware run rake.


To generate doxygen documentation run rake doc.


There are two firmware images: bootloader and application. The bootloader image allows to flash the application over USB using the DFU protocol. The bootloader is started first and immediately jumps to the application if it is valid and the DFU mode is not forced (i.e. by pressing the user button on the board or requesting a DFU detach in the application). The application image is the main application and is implemented in application.c. It is up to the application to advertise USB DFU support (i.e. as does the provided USB CDC ACM example).

The simplest way do flash the bootloader image is using the embedded bootloader. By pressing the BOOT0 button (setting the pin low) while powering or resetting the device, the micro-controller boot its embedded UART/USB DFU bootloader. Connect a USB cable and run rake dfu_bootloader.

Once the bootloader is flashed, it is possible to flash the application over USB using the DFU protocol by running rake flash (equivalent to rake dfu_application. To force the bootloader to start the DFU mode press the user button or short a pin, depending on the board. Note: I use my own DFU bootloader instead of the embedded bootloader because I was not able to start the embedded USB DFU bootloader from the application.

The images can also be flash using SWD (Serial Wire Debug) in case the firmware gets stuck and does not provide USB functionalities. For that you need an SWD adapter. The Makefile uses a ST-Link V2 programmer along OpenOCD software (default), or Black Magic Probe. To flash the bootloader using SWD run rake swd_bootloader (this will also erase the application). To flash the application using SWD run rake swd_application (or rake swd). To erase all memory and unlock read/write protection, run rake remove_protection.


SWD also allows to debug the code running on the micro-controller using GDB. To start the debugging session run rake debug.


The firmware offers serial communication over USART1 and USB (using the CDC ACM device class).