Pico Tyre Temperature Monitor - CAN Bus Version

High-performance thermal tyre and brake temperature monitoring for Adafruit RP2040 CAN Bus Feather

Real-time thermal imaging at 10 fps with automatic tyre detection, brake pad temperature monitoring, and CAN bus output for vehicle integration.

Features

CAN Bus Output - Configurable CAN 2.0A (125K-1M kbps) for vehicle integration
Multi-Board Support - Up to 4 boards (one per wheel) on same CAN bus
Brake Temps - MCP9601 Type-K thermocouple support for brake pads
Fast - 10 fps thermal imaging with automatic tyre detection
Reliable - Automatic sensor recovery, watchdog protection
Safe - Integer overflow protection, bounds checking, flash verification
Visual Feedback - NeoPixel status LED with color-coded states

Hardware

Parts List

Component	Qty	Link
Adafruit RP2040 CAN Bus Feather	1 per wheel	Pimoroni
MLX90640 Thermal Camera Breakout	1 per wheel	Pimoroni
MCP9601 Thermocouple Amplifier (optional)	0-2 per wheel	Pimoroni
Type-K Thermocouple (optional)	0-2 per wheel	-
STEMMA QT / Qwiic cables	as needed	-

All three boards have STEMMA QT / Qwiic connectors - just daisy-chain with cables, no soldering for I2C.

Wiring

I2C (STEMMA QT cables, no soldering):

Feather QT port → MCP9601 (inner) → MCP9601 (outer) → MLX90640

Power and CAN (soldering required):

Feather Terminal Block     Vehicle
----------------------     -------
CAN-H                  →   CAN-H
CAN-L                  →   CAN-L
GND                    →   GND

Feather USB Header         Power Source
------------------         ------------
5V pad                 →   +12V via regulator or USB power

Add 120Ω termination resistor between CAN-H and CAN-L if sensor is at end of bus.

I2C Addresses

Device	Address
MLX90640 thermal camera	0x33
MCP9601 inner brake temp	0x65
MCP9601 outer brake temp	0x66

Quick Start

1. Build

# Clone and build
git clone https://github.com/SamSkjord/pico-tyre-temp.git
cd pico-tyre-temp
git checkout canbus-feather

# Build (sets up toolchain paths automatically)
./build.sh

# Output: build/thermal_tyre_canbus.uf2

2. Flash

Hold BOOTSEL button and plug in USB
Copy build/thermal_tyre_canbus.uf2 to RPI-RP2 drive
Feather reboots and starts running

3. Configure

Each sensor must be configured for its wheel position before installation.

Initial Setup (USB Serial)

Connect sensor to computer via USB

Open serial terminal (115200 baud):

screen /dev/tty.usbmodem* 115200   # macOS/Linux

Configure wheel position:

WHEEL=0     # Front Left (CAN base 0x100)
WHEEL=1     # Front Right (CAN base 0x120)
WHEEL=2     # Rear Left (CAN base 0x140)
WHEEL=3     # Rear Right (CAN base 0x160)

Verify configuration:
```
STATUS
```
Output shows wheel ID, CAN base ID, and board serial number.

Optional settings:

EMISSIVITY=95    # Tyre emissivity (default 95 = 0.95)
MODE=0           # 0=tyre detect, 4/8/16=fixed channels
BROADCAST=1      # 1=auto 10Hz, 0=on-request only
CANSPEED=500     # CAN bus speed (125/250/500/1000 kbps)

Configuration persists in flash across power cycles.

Multi-Sensor Setup

When setting up multiple sensors:

Label each board with its wheel position before configuration
Configure one at a time via USB before installation
Record board serial numbers (shown in STATUS output) for remote configuration later

Remote Configuration (CAN)

Once installed, sensors can be reconfigured via CAN without USB access.

Discover sensors - Send CONFIG_REQUEST (0x7F1):
```
CAN TX: ID=0x7F1 Data=[0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
```
Each sensor responds with CONFIG_RESPONSE (0x7F2) containing its wheel ID and serial.
Change wheel ID - Send CONFIG_SET_WHEEL (0x7F0):
```
CAN TX: ID=0x7F0 Data=[serial0, serial1, serial2, serial3, new_wheel_id, 0, 0, 0]
```
Where serial0-3 are the first 4 bytes of the target board's serial number.
Change other settings - Similar format for 0x7F4-0x7F6:
- CONFIG_SET_EMISSIVITY (0x7F4): [...serial..., emissivity, 0, 0, 0]
- CONFIG_SET_MODE (0x7F5): [...serial..., mode, 0, 0, 0]
- CONFIG_SET_BROADCAST (0x7F6): [...serial..., broadcast, 0, 0, 0]

Verification

After configuration, verify CAN output:

Connect CAN analyser to vehicle bus
Load pico_tyre_temp.dbc for signal decoding
Check messages appear at correct base ID for wheel position:
- FL: 0x100-0x11C
- FR: 0x120-0x13C
- RL: 0x140-0x15C
- RR: 0x160-0x17C

Factory Reset

To reset a sensor to defaults (wheel 0, emissivity 95%, auto broadcast):

RESET

Quick Reference

Wheel	ID	CAN Base	USB Command
Front Left	0	0x100	`WHEEL=0`
Front Right	1	0x120	`WHEEL=1`
Rear Left	2	0x140	`WHEEL=2`
Rear Right	3	0x160	`WHEEL=3`

CAN Bus Protocol

A DBC file (pico_tyre_temp.dbc) is included for use with CAN analysis tools (Vector CANalyzer, SavvyCAN, etc).

Message IDs

Each wheel has a unique base CAN ID with message offsets:

Message	Offset	Rate	Content
TYRE_TEMPS	+0x00	10Hz	Left/Centre/Right temps, lateral gradient (detect mode)
TYRE_DETECTION	+0x01	10Hz	Detection status, confidence, width (detect mode)
BRAKE_TEMPS	+0x02	10Hz	Inner/outer brake temps, status
STATUS	+0x10	1Hz	FPS, firmware version, frame number
RAW_CH_A	+0x18	10Hz	Channels 0-3 temps (channel modes)
RAW_CH_B	+0x19	10Hz	Channels 4-7 temps (8/16 channel modes)
RAW_CH_C	+0x1A	10Hz	Channels 8-11 temps (16 channel mode)
RAW_CH_D	+0x1B	10Hz	Channels 12-15 temps (16 channel mode)
FRAME_DATA	+0x1C	On-demand	Full 768-pixel thermal frame (256 segments)

Configuration Messages (Broadcast)

CAN ID	Message	Direction
0x7F0	CONFIG_SET_WHEEL	RX
0x7F1	CONFIG_REQUEST	RX
0x7F2	CONFIG_RESPONSE	TX
0x7F3	FRAME_REQUEST	RX
0x7F4	CONFIG_SET_EMISSIVITY	RX
0x7F5	CONFIG_SET_MODE	RX
0x7F6	CONFIG_SET_BROADCAST	RX
0x7F7	DATA_REQUEST	RX
0x7F8	CONFIG_SET_CANSPEED	RX

Example: Front Left Wheel (ID 0)

CAN ID	Message
0x100	Tyre temperatures
0x101	Tyre detection
0x102	Brake temperatures
0x110	Status
0x11C	Frame data segments

Data Format

All multi-byte values are little-endian. Temperatures in tenths of °C (int16).

TYRE_TEMPS (8 bytes)

Byte 0-1: Left median temp (int16, tenths °C)
Byte 2-3: Centre median temp (int16, tenths °C)
Byte 4-5: Right median temp (int16, tenths °C)
Byte 6-7: Lateral gradient (int16, tenths °C)

BRAKE_TEMPS (8 bytes)

Byte 0-1: Inner brake temp (int16, tenths °C)
Byte 2-3: Outer brake temp (int16, tenths °C)
Byte 4: Inner sensor status (0=OK, 1=Disconnected, 2=Error, 3=Not Found)
Byte 5: Outer sensor status
Byte 6-7: Reserved

Full Frame Streaming

Request a full 768-pixel thermal frame by sending FRAME_REQUEST (0x7F3):

Byte 0: Target wheel ID (0-3, or 0xFF for any)
Byte 1-7: Reserved

The board responds with 256 FRAME_DATA segments (Base + 0x1C):

Byte 0-1: Segment index (0-255, uint16)
Byte 2-3: Pixel N+0 temp (int16, tenths °C)
Byte 4-5: Pixel N+1 temp (int16, tenths °C)
Byte 6-7: Pixel N+2 temp (int16, tenths °C)

Pixels are sent in row-major order (24 rows x 32 columns = 768 pixels). At 8 segments per main loop iteration (~10Hz), full transfer takes ~3.2 seconds.

Remote Configuration

Configure boards remotely via CAN (requires board serial number from CONFIG_RESPONSE):

CONFIG_SET_EMISSIVITY (0x7F4)

Byte 0-3: Target board serial (first 4 bytes)
Byte 4: Emissivity (10-100)
Byte 5-7: Reserved

CONFIG_SET_MODE (0x7F5)

Byte 0-3: Target board serial (first 4 bytes)
Byte 4: Channel mode (0=detect, 4, 8, or 16)
Byte 5-7: Reserved

CONFIG_SET_BROADCAST (0x7F6)

Byte 0-3: Target board serial (first 4 bytes)
Byte 4: Broadcast mode (0=request, 1=auto)
Byte 5-7: Reserved

CONFIG_SET_CANSPEED (0x7F8)

Byte 0-3: Target board serial (first 4 bytes)
Byte 4-5: CAN speed in kbps (125, 250, 500, or 1000, uint16 LE)
Byte 6-7: Reserved

Note: CAN speed change requires reboot to take effect.

CONFIG_RESPONSE (0x7F2) - sent in reply to CONFIG_REQUEST (0x7F1):

Byte 0: Wheel ID
Byte 1-4: Board serial (first 4 bytes)
Byte 5: Firmware version
Byte 6: Emissivity (0-100)
Byte 7: Channel mode

Status LED

Color	Meaning
Green	Normal operation
Yellow	Warning (high gradient, thermocouple issue)
Red	Sensor error (MLX90640 disconnected)
Blue	CAN bus error
Purple	Initialization/configuration mode
White flash	Heartbeat (every second)

USB Serial Commands

WHEEL=n       Set wheel ID (0-3)
EMISSIVITY=n  Set emissivity (10-100, e.g., 95 = 0.95)
MODE=n        Set channel mode (0=detect, 4, 8, or 16)
BROADCAST=n   Set broadcast mode (0=on-request, 1=auto)
CANSPEED=n    Set CAN bus speed (125/250/500/1000 kbps, requires reboot)
STATUS        Show current configuration
RESET         Reset to defaults
HELP          Show available commands

Channel Modes

The sensor supports two types of operation: automatic tyre detection (mode 0) or fixed channel modes (4/8/16).

Mode 0: Tyre Detection (default)

Automatically detects tyre edges and reports left/centre/right zone temperatures. Best when the sensor has a clear view of the full tyre width with background on both sides.

CAN messages at 10Hz: TYRE_TEMPS, TYRE_DETECTION, BRAKE_TEMPS

Fixed Channel Modes (4/8/16)

Divides the sensor's 32 columns into equal groups spanning the full tyre width. Each channel reports the median temperature from the middle 4 rows (rows 10-13) of its column group. Use these modes when sensor mounting doesn't suit automatic detection.

4-channel mode - 8 columns per channel:

Columns:  0-7      8-15     16-23    24-31
          |--------|--------|--------|--------|
Channel:     0        1        2        3
          |------------- RAW_CH_A -------------|

CAN messages at 10Hz: RAW_CH_A, BRAKE_TEMPS

8-channel mode - 4 columns per channel:

Columns:  0-3    4-7    8-11   12-15  16-19  20-23  24-27  28-31
          |------|------|------|------|------|------|------|------|
Channel:    0      1      2      3      4      5      6      7
          |-------- RAW_CH_A ---------|--------- RAW_CH_B --------|

CAN messages at 10Hz: RAW_CH_A, RAW_CH_B, BRAKE_TEMPS

16-channel mode - 2 columns per channel:

Columns:  0-1  2-3  4-5  6-7 | 8-9 10-11 12-13 14-15 | 16-17 18-19 20-21 22-23 | 24-25 26-27 28-29 30-31
Channel:   0    1    2    3  |  4    5     6     7   |   8     9    10    11   |  12    13    14    15
          |--- RAW_CH_A ----||---- RAW_CH_B --------||---- RAW_CH_C ----------||---- RAW_CH_D --------|

CAN messages at 10Hz: RAW_CH_A, RAW_CH_B, RAW_CH_C, RAW_CH_D, BRAKE_TEMPS

Summary

Mode	Columns/Channel	CAN Messages (10Hz)
0 (detect)	Auto zones	TYRE_TEMPS, TYRE_DETECTION, BRAKE_TEMPS
4	8	RAW_CH_A, BRAKE_TEMPS
8	4	RAW_CH_A, RAW_CH_B, BRAKE_TEMPS
16	2	RAW_CH_A-D, BRAKE_TEMPS

All modes also send STATUS at 1Hz.

Broadcast Mode

Mode	Description
1 (Auto)	Continuous 10Hz transmission (default)
0 (Request)	Only transmit when DATA_REQUEST (0x7F7) received

In request mode, send DATA_REQUEST with target wheel ID to trigger a single data transmission:

Byte 0: Target wheel ID (0-3, or 0xFF for all)
Byte 1-7: Reserved

Safety Features

Watchdog timer - 2s timeout, auto-recovery from hangs
Sensor recovery - Automatic re-initialization on failure (max 10 attempts)
Integer overflow protection - Safe temperature conversions
Flash verification - Confirms writes before proceeding
Bounds checking - Validates all inputs and array accesses

Build Requirements

Component	Path	Notes
Pico SDK	`~/pico-sdk`	Clone from raspberrypi/pico-sdk
ARM Toolchain	`~/arm-toolchain/arm-gnu-toolchain-14.2.rel1-*`	Official ARM release

Note: Homebrew's arm-none-eabi-gcc won't work due to missing newlib.

Manual Build

export PATH="$HOME/arm-toolchain/arm-gnu-toolchain-14.2.rel1-darwin-arm64-arm-none-eabi/bin:$PATH"
export PICO_SDK_PATH="$HOME/pico-sdk"

./tools/download_mlx_library.sh  # First time only
rm -rf build && mkdir build && cd build
cmake .. && make -j4

File Structure

pico-tyre-temp/
├── main.c                  # Main application loop
├── thermal_algorithm.c/h   # Tyre detection algorithm
├── can_bus.cpp/h           # CAN controller driver (C++)
├── config.c/h              # Flash configuration storage
├── status_led.c/h          # NeoPixel driver (PIO)
├── mcp9601.c/h             # Thermocouple driver
├── communication.c/h       # USB serial output
├── ws2812.pio              # PIO program for NeoPixel
├── build.sh                # Build script
├── CMakeLists.txt          # CMake configuration
├── CLAUDE.md               # Developer documentation
└── mlx90640/               # Melexis driver library

Troubleshooting

"ERROR: Could not detect MLX90640 sensor"

Check wiring (3.3V, not 5V!)
Verify 4.7kΩ pull-ups on SDA/SCL
Check I2C address (0x33)

CAN messages not appearing

Verify CAN-H/CAN-L wiring
Check 120Ω termination
Confirm baud rate matches receiver (default 500 kbps, check with STATUS command)

Red LED stays on

Sensor error - check MLX90640 connection
System will attempt recovery every 5 seconds

Blue LED

CAN bus error - check wiring and termination
May indicate bus-off condition

Version History

v2.0 (2025-01) - CAN Bus Version

New hardware - Adafruit RP2040 CAN Bus Feather
CAN output - 500 kbps CAN 2.0A replaces I2C slave
Multi-board - Support for 4 boards on same bus
Brake temps - MCP9601 thermocouple support
NeoPixel LED - Color-coded status indication
Safety features - Overflow protection, sensor recovery, watchdog

v1.x - Original Pico Version

Raspberry Pi Pico with I2C slave output
See main branch for original version

License

MIT License

Credits

MLX90640 driver from Melexis
CAN driver based on pico-mcp2515
Built with Raspberry Pi Pico SDK

Name		Name	Last commit message	Last commit date
Latest commit History 41 Commits
mlx90640		mlx90640
tools		tools
.gitignore		.gitignore
CLAUDE.md		CLAUDE.md
CMakeLists.txt		CMakeLists.txt
README.md		README.md
build.sh		build.sh
can_bus.cpp		can_bus.cpp
can_bus.h		can_bus.h
communication.c		communication.c
communication.h		communication.h
config.c		config.c
config.h		config.h
main.c		main.c
mcp9601.c		mcp9601.c
mcp9601.h		mcp9601.h
pico_tyre_temp.dbc		pico_tyre_temp.dbc
status_led.c		status_led.c
status_led.h		status_led.h
thermal_algorithm.c		thermal_algorithm.c
thermal_algorithm.h		thermal_algorithm.h
ws2812.pio		ws2812.pio

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Pico Tyre Temperature Monitor - CAN Bus Version

Features

Hardware

Parts List

Wiring

I2C Addresses

Quick Start

1. Build

2. Flash

3. Configure

Initial Setup (USB Serial)

Multi-Sensor Setup

Remote Configuration (CAN)

Verification

Factory Reset

Quick Reference

CAN Bus Protocol

Message IDs

Configuration Messages (Broadcast)

Example: Front Left Wheel (ID 0)

Data Format

Full Frame Streaming

Remote Configuration

Status LED

USB Serial Commands

Channel Modes

Mode 0: Tyre Detection (default)

Fixed Channel Modes (4/8/16)

Summary

Broadcast Mode

Safety Features

Build Requirements

Manual Build

File Structure

Troubleshooting

Version History

v2.0 (2025-01) - CAN Bus Version

v1.x - Original Pico Version

License

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