firmware for the Bahn Uhr controller.

project

summary

This is the controller for a salvaged and modded Bahnsteig Uhr:

• the track is made of white translucent ceramic, and RGBW LED strips illuminate it
• a motor uses the dial drive to turn the dials (in theory with settable time)
• LED panels allow to show text on both sides
• controllable over the network using Art-Net

technology

controller comprises:

• a STM32 F4 series micro-controller-based black pill
• a DRV8825 stepper motor allows turning the dials (hour is linked to minute)
• reed switch, to home dial
• P1 RGB LED panel (128x64), to display text on front side
• WS2812b panel (2x 32x8), to display text
• nMOS transistors to control 12V LED strips, to illuminate the track
• ESP8266-based ESP-01 to connect to network
• power connectors (0,5,12V-4pin and 12V-barrel input, 5V outputs for LED panels, 12V for motor and LED strips)

Art-Net

The Bahn Uhr controller gets data over the network using Art-Net. The mapping is as follows (universe without offset, channel, target).

clock illumination color (RGBW LED strip):

• 0, 0, red high byte
• 0, 1, red low byte
• 0, 2, green high byte
• 0, 3, green low byte
• 0, 4, blue high byte
• 0, 5, blue low byte
• 0, 4, white high byte
• 0, 5, white low byte

dials position:

• 1, 0, hours (0-11)
• 1, 1, minutes (0-59)
• 1, 2, seconds (0-59)
• 1, 3, direction
• 1, 4, speed

text display:

font display, line 1:

• 2, 0, red intensity (0 to use clock illumination color)
• 2, 1, green intensity (0 to use clock illumination color)
• 2, 2, blue intensity (0 to use clock illumination color)
• 2, 3, horizontal position (0 is left), high signed byte
• 2, 3, horizontal position (0 is left), low byte
• 2, 4+, text (NULL ended)

font display, line 2:

• 3, 0, red intensity (0 to use clock illumination color)
• 3, 1, green intensity (0 to use clock illumination color)
• 3, 2, blue intensity (0 to use clock illumination color)
• 3, 3, horizontal position (0 is left), high signed byte
• 3, 3, horizontal position (0 is left), low byte
• 3, 4+, text (NULL ended)

font display, line 3:

• 4, 0, red intensity (0 to use clock illumination color)
• 4, 1, green intensity (0 to use clock illumination color)
• 4, 2, blue intensity (0 to use clock illumination color)
• 4, 3, horizontal position (0 is left), high signed byte
• 4, 3, horizontal position (0 is left), low byte
• 4, 4+, text (NULL ended)

back display, line 1:

• 5, 0, red intensity (0 to use clock illumination color)
• 5, 1, green intensity (0 to use clock illumination color)
• 5, 2, blue intensity (0 to use clock illumination color)
• 5, 3, horizontal position (0 is left), high signed byte
• 5, 3, horizontal position (0 is left), low byte
• 5, 4+, text (NULL ended)

back display, line 2:

• 6, 0, red intensity (0 to use clock illumination color)
• 6, 1, green intensity (0 to use clock illumination color)
• 6, 2, blue intensity (0 to use clock illumination color)
• 6, 3, horizontal position (0 is left), high signed byte
• 6, 3, horizontal position (0 is left), low byte
• 6, 4+, text (NULL ended)

board

The underlying template also supports following board:

• WeAct MiniF4, based on a STM32F401CCU6

connections

Connect the peripherals the following way (STM32F4xx signal; STM32F4xx pin; peripheral pin; peripheral signal; comment):

• list board to peripheral pin connections

DRV8825 stepper motor driver (using one timer for PWM output):

• STEP: PA15/TIM2_CH1
• DIRECTION: PB15
• nSLEEP: PB14, shorted to nRESET
• nRESET: PB14, with external 10kOhm pull-down resistor
• nENABLE: PB13, with external 10kOhm pull-up resistor
• FAULT: PB12, with external 10kOhm pull-up resistor

reed switch, to home dial position:

• 1: GND
• 2: PB4

LED driver (using one timer for PWM outputs):

• gate 0: PB6/TIM4_CH1
• gate 1: PB7/TIM4_CH2
• gate 2: PB8/TIM4_CH3
• gate 3: PB9/TIM4_CH4

WS2812b LED matrix:

• DOUT: PB5 (SPI1_MOSI)

RGB matrix (using one DMA)

• DR1: PA2
• DG1: PA3
• DB1: PA4
• DR2: PA5
• DG2: PA6
• DB2: PA7
• CLK: PA0
• LAT: PA1
• A: PB0
• B: PB1
• C: PB2
• D: PB3
• OE: PB10

ESP8266-based ESP-01 (using one UART):

• RX: PA9/USART1_TX
• TX: PA10/USART1_RX

EN is pulled to VCC using 10 kOhm for the ESP to start. I replaced the 1 MB flash with a 4MB flash to be sure I won't be annoyed by the space limit. I flashed the AT firmware from ESP8266_NONOS_SDK-3.0.5:

esptool.py --chip auto --port /dev/ttyUSB0 --baud 115200 erase_flash
esptool.py -p /dev/ttyUSB0 --chip esp8266 write_flash -fm dio -ff 26m --flash_size 2MB-c1 0x00000 ./bin/boot_v1.7.bin 0x01000 ./bin/at/1024+1024/user1.2048.new.5.bin 0x1fc000 ./bin/esp_init_data_default_v08.bin 0xfe000 ./bin/blank.bin 0x1fe000 ./bin/blank.bin 0x1fb000 ./bin/blank.bin

to test the firmware, issue AT commands:

picocom -b 115200 /dev/ttyUSB0 --omap crcrlf
AT

OK

AT+GMR
version information

configure the access point in flash:

# set station mode
AT+CWMODE_DEF=1
# set AP credentials
AT+CWJAP_DEF="essid","password"

free:

• PB4, PB5
• PA8/TIM1_CH1

used:

• PA12: USB DP
• PA11: USB DM
• PC13: LED
• PC14/PC15: 32kHz XTAL

All pins are configured using defines in the corresponding source code.

code

dependencies

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.

firmware

To compile the firmware run rake.

documentation

To generate doxygen documentation run rake doc.

flash

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.

debug

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

USB

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