STM32 Switch Table for SZEmission

The switch table is the "brain" of the car, used for controlling most functions like lights, wiper, and brake. It processes the inputs from the switches, steering wheel and pedal then compiles them into it's state and sends that out over the CAN bus. It can also send motor control commands when the override switch is turned off.

Features

• State Broadcasting: Sends a CAN message az 20Hz about its own state (switch positions, throttle position)
• Wiper Control: Controls the wiper converter and servo with PWM
• Throttle Input: Reads and filters the analog potentiometer on the throttle pedal
• Motor Control: Optionally sends motor control CAN messages

Communication Protocols

This controller uses 4 types of IO to achieve its functionality:

• CAN bus for communicating with the various components of the car
• GPIO to read switch positions and control some outputs
• ADC (Analog to Digital conversion) to read the throttle pedal potentiometer
• PWM for controlling the wiper servo motor

CAN Bus Messages

Received Messages

ID	ID Type	Name	Purpose
0x185	Standard	Sync State	myRIO status message (used for autonomous driving)
0x190	Standard	Steering Wheel	State of buttons and position of switches on the steering wheel
0x123	Standard	RPM Measurement	RPM data from the encoder (motor position sensor)

Steering Wheel State (0x190) Bit Fields

Byte 0 (STW_STATE_A):
  Bit 0: ACC (Accelerate using predefined speed profile)
  Bit 1: DRIVE (Drive Mode)
  Bit 2: REVERSE (Reverse Mode)
  Bit 3: LAP (End of lap button)
  Bit 4: TS_L (Turn signal left)
  Bit 5: TS_R (Turn signal right)
  Bit 6: FUNCTION1 (Reserved)
  Bit 7: FUNCTION2 (Reserved)

Bytes 1-3: Position of the 3 switches on the steering wheel (STW_STATE_B/C/D)

Transmitted Messages

ID	Type	Purpose	Data Format	Rate
0x129	Standard	VCU State	Bytes 0-1: VCU_STATE_A/B, Bytes 2-5: Throttle % (fixed-point)	20Hz
0xA51	Extended	Motor Control	Bytes 0-3: Throttle reference (fixed-point, signed)	20Hz

VCU State (0x129) Bit Fields

Byte 0 (VCU_STATE_A):
  Bit 0: HEADLIGHT
  Bit 1: HAZARD
  Bit 2: AUTO  (Autonomous driving mode)
  Bit 3: BRAKE (Brake pedal pressed)
  Bit 4: LIGHTS_ENABLE
  Bit 5: MC_OW (Disables motor control messages)
  Bit 6: WIPER
  Bit 7: Reserved

Byte 1 (VCU_STATE_B):
  Bit 0: RELAY_NO (Shell relay)
  Bit 1: RELAY_NC (Shell relay)
  Bits 2-7: Reserved

Code Structure

This project is designed to minimize the amount of user code in generated files. The main working logic is in user.c and user.h.

Directory Breakdown

sw_table_stm32/
├── sw_table_stm32.ioc            # STM32CubeIDE pin/peripheral configuration
├── Core/
│   ├── Inc/
│   │   ├── main.h               # Generated header (mostly for pin definitions)
│   │   └── user.h               # User definitions of functions and structures
│   ├── Src/
│   │   ├── main.c               # Entry point and initialization
│   │   └── user.c               # User-defined functions (core logic)

Key Files

• main.c: System initialization, timer and CAN setup, interrupt handlers and main loop entry point
• user.h: Data structures, function declarations and constants
• user.c: Core application logic including CAN communication, GPIO control, and throttle ADC processing

Timer Configuration

• TIM1: Base timer for interval management (1ms period)
  • Used for CAN message intervals (20Hz)
  • Used for wiper control intervals (750ms)
• TIM2: PWM timer for wiper servo control (50Hz clock)

Test hardware

Nucleo C092RC Development Board

• Microcontroller: STM32C092RCTx (LQFP64)
• Clock: Internal HSI oscillator running at 48MHz
• CAN Interface: FDCAN1 using the on-board CAN transceiver
• Programmer/Debugger: Nucleo built-in ST-Link

Pin Configuration

CAN Bus

Function	Name	Test Pin
CAN receive	FDCAN1_RX	PC2
CAN transmit	FDCAN1_TX	PC3

GPIO Inputs

Function	Name	Test Pin
Switch used to enable lights	SW_LIGHTS	PC8
Wiper on/off	SW_WIPER	PC6
Hazard signal	SW_HAZARD	PC13
Autonomous mode switch	SW_AUTO	PC11
Motor control override	SW_MC_OW	PC7
Headlight switch	SW_HEADLIGHT	PC0
Shell relay input	IN_SHELL_RELAY	PC1
Brake pedal input	IN_BRAKE	PC12

GPIO Outputs

Function	Name	Test Pin
Wiper DC -> DC converter enable	OUT_WIPER_CONVERTER	PD3

ADC Input

Function	Name	Test Pin
Throttle pedal potentiometer	ADC1_IN0	PA0

PWM Output

Function	Timer	Channel	Test Pin
Wiper servo control	TIM2	CH1	PA5

Development Guidelines

• Use fixed-point math instead of floating-point (no FPU)
• Keep interrupt callbacks short: Set flags and do the actual processing in main loop

Power Optimization

Work in progress, once final hardware is finished.

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Created by SZEnergy Team for Shell Eco Marathon

• Váradi Marcell (varma02@GitHub)