Pedal & Button Controller (eng)

During building my pedals, I decided to make my own pedal controller using cheep and affordable components. Already having some  experience with Arduino boards, I know their capabilities and decided to route a STM32 way this time (mostly to learn something new though).

Here is the comparision of Arduino Leonardo (which is a most likely candidate for our goal) and STM32F103C8T6 (which I used)

	Arduino Leonardo	STM32F103C8T6
Flash	32KB	64KB
SRAM	2.5KB	20KB
EEPROM	1KB	Absent
Architecture	8-bit ATMEL AVR	32-bit ARM CORTEX-M3
Frequency	16MHz	up to 72MHz
GPIO pins	20	26
PWM	7	12
Timers	1x 16-bit, 2x 8-bit	3x 16-bit, 1x pwm
Peripheral	10-bit ADC (6 channels) 1x I2C 1x SPI 1x UART USB	2 x 12-bit, 1 μs A/D converters (7 channels) 7-channel DMA controller 3x USART 2x I2C 2x SPI CAN USB

As you can see, specs for stm32f103c8 are not so bad. And it’s cheaper than Leonardo!

One big drawback is that you need additional external programmer. But its not expensive also, total price for mini board + programmer is still comparable with Arduino clones.

• 

• 

I bought both items on aliexpress.com, search for «STM32F103C8T6 Minimum System Development Board» and «ST-Link v2 mini», for example this and this. Also there is another version of the board called BlackPill — link. It has less available pins, but has mounting holes.

Schematics for the dev board: 

Or here in pdf

Pinout in pdf — The-Generic-STM32F103-Pinout-Diagram

Black_Pill_Schematic

So, after some time, I programmed simracing-oriented firmware for the device.

Device capabilities are:

• Gamepad/Keyboard/Mouse emulation
• 6x 12-bit (4096 steps) axises
• rotary encoders support
• rotary switches support
• matrix buttons support
• single buttons support
• axes calibration, axes shaping
• analog inputs as buttons
• 1kHz exchange rate with PC, which means 1ms maximum latency for axes

It can be used for DIY buttons boxes, button rim plates, pedals, hand brakes, gear shifters, etc, etc — everywhere you need gamepad/keyboard/mouse interface with PC. Its usual HID device, no additional drivers installation needed.

Here is pinout you get after flashing the firmware first time:

             STM32F103C8T6
	   -------------------
	- |3VB		 +3.3V| -
  	- |C13		   GND| -
  COL1	- |C14		   +5V| - 
  COL2	- |C15		    B9| - ROW6
  ADC0 	- |A0		    B8| - ROW5
  ADC1 	- |A1		    B7| - ROW4
  ADC2	- |A2		    B6| - ROW3
  ADC3	- |A3		    B5| - ROW2
  ADC4	- |A4		    B4| - ROW1
  ADC5	- |A5		    B3| - COL4
  ADC6	- |A6		   A15| - ROT11
  COL5	- |A7		   A12| - 
  ROT1	- |B0		   A11| - 
  ROT2	- |B1		   A10| - ROT8
  ROTA	- |B10		    A9| - ROT7
  ROTB	- |B11		    A8| - ROT6
	- |R		   B15| - ROT5
	- |+3.3V	   B14| - ROT4
	- |GND		   B13| - ROT3
	- |GND		   B12| - COL3
	   -------------------

Also I programmed small PC-based app named OSHStudio, which allows you to choose a function for each pin. Pins’ functions can be selected in the «Pins Configuration» tab, also here you can choose your board type. Here is how the initial pinout looks in OSHStudio, when you click «Get Config from Device»:

Mouse

You can configure analog input pin as 1 of 2 mouse axes or mouse’s wheel. Left/Middle/Right buttons can be configured on the Buttons Tab.

Buttons

When buttons wired in matrix, columns have to be connected to Button Matrix COLUMNS pins, rows — to Button Matrix ROWS pins. Single separate buttons (not matrix), can be connect to «Single Button +3,3V» or «Single Button GND». If you connect button to «Single Button +3.3V» than connect the other side of button to +3.3V, if you connect button to «Single Button GND» than connect it to GND. Here is an example of matrix wiring:

You can test your buttons in the «Buttons» tab of OSHStudio. Also you can choose «function» for each button — how it’ll be act at PC — as gamepad button, keyboard key, etc. All buttons are configured as gamepad button as default.

Rotary Encoders

The firmware supports full step, half step and quarter step encoders. Rotary encoders can be wired in «chained» or «single» configuration. Chained config means you wire side encoders’ pins (PINA & PINB) together and central pin become «control» pin. Central pin identified your encoder type — 1/1 (full step), 1/2 (half step) or 1/4 (quarter step). You can wire different type encoders in one chain.

Schematics:

Also encoders can be connected in single configuration. In this case you should configure side pins according to the type of encoder and central pin have to be connected to +3.3V.

Schematics:

If necessary you can remap encoders pins on the «Single Encoders Config» tab.

Encoders can also be tested in the «Buttons» tab.

Rotary Switches

Virtual button is «clicked» when shaft is changing position.

Axes

Analog pins ADC0 — ADC6 used to connect potentiometers or other analog inputs. Also you can calibrate axises in OSHStudio, and calibration values in this case will be stored in MCU itself. After calibration an axis is «expanded» by the controller, so PC always sees axis as 4096 steps. There is also a possibility of AutoCalibration of axes. Raw sensor value is shown as RED scale (there is no impact of calibration on it) and axis value is shown as GREEN scale (direct impact of calibration).

As you can see, there is also «Combined axis» function. It means you can combine 2 analog inputs in one axis. The function is mainly intended for rims with 2 clutch paddles. There are 2 possible modes:

• cooperative work — in this mode results from both analog inputs are summarized. You can choose weight of each input by slider.
• each on his own — each analog input works independently but for one axis. For example you can short calibrate an one input (paddle) for fast gear changes and an other calibrate as normal axis — for starting.

Also you can make axis shaping. There are 6 predefined shape presets and you can modify them as you want and give them its own name

Analog2Button 

Beginning with 0.15 version there is a more advanced possibility to map analog iinputs to buttons. You can configure up to 10 analog inputs and each of them can be mapped up to 10 buttons (keep in mind though total number of buttons is still 64). You can define it in the Analog2Buttons tab

Tuning Tab

You can tune such parameters as:

• «Your identifier for the device» — unique identifier for the board, if you have for example few boards, you can assign different idetigiers to them — «pedals», «buttonsbox», etc
• «USB polling interval» — means interval between USB packets, i.e. 1ms means 1kHz USB exchange frequency. For high performance devices you can try decrease this down to 1ms, for anything else default 16ms probably is enough.
• «Amount of time a button will be pressed when Rotary Encoder position changed» — virtual button will appear as pressed during this time, for encoders
• «Amount of time a button will be pressed when Rotary Switch position changed» -virtual button will appear as pressed during this time, for rotary switches
• «Amount of time a button will be pressed when Analog Input position changed» -virtual button will appear as pressed during this time, for analog2buttons inputs
• «Time since previous Rotary Switch change» — if you change rotary switch position in less time than the parameter then buttons presses will not be registered. So if you rotate switch fast enough then intermediate positions will not be registered.
• «Time since previous Analog Input position change» — same as previous one, but for Analog2Buttons types
• «Debounce time for Rotary Encoders» and «Debounce time for Buttons» — try to increase it if you have problem with phantom presses

Notes

I recommend set to «Not used» all unused pins 🙂

Source code in my github project.

Available firmware + OSHStudio app:

Version 0.16 — keyboard/mouse emulation, buttons functions, axes shaping

Version 0.15 — More stable USB operations, more advanced Analog2Buttons type

Version 0.14 — Autocalibration axes, Analog2Button pin type and combined axis added

Version 0.13 — Single Encoders Config tab added

Version 0.12 — Tuning tab added

Version 0.11 — Single encoders support added

Version 0.10 — base version

If you wonder how to flash firmware to the board you can check this post — How to flash firmware to STM32Fx