RaceTemp_BLE

RaceTemp_BLE is an STM32WB55 based Bluetooth Low Energy sensor bridge for RaceChrono. It reads local sensors, packages the measurements as RaceChrono DIY CAN/BLE messages, and lets RaceChrono log them as if they came from a CAN bus.

The project is based on the RaceChrono BLE DIY device idea from Aollin's demo project:

https://github.com/aollin/racechrono-ble-diy-device

RaceTemp adds the temperature, pressure, thermocouple, RPM, engine-hours, and engine-revolutions logic used by this project.

Current Status

This firmware is still a work in progress.

Implemented:

• BLE device name: RaceTemp
• RaceChrono-compatible CAN message characteristic
• Optional RaceChrono CAN filter handling
• ADC based MAP and NTC readings
• MAX31855 thermocouple support
• MAX31856 thermocouple support
• Ignition input based RPM measurement
• Engine operating hours counter
• Engine revolutions counter
• Persistent storage of engine counters after the engine stops
• Optional raw measurement snapshot message

Hardware Notes

Target MCU:

• STM32WB55CGU

The project has been developed around the WeAct STM32WB55 core board.

Thermocouple IC options:

• MAX31855
• MAX31856

The thermocouple IC is selected at compile time in:

Core/Inc/RaceTemp_config.h

Thermocouple Polarity

Do not trust wire color blindly. For many Type K thermocouples using US/ANSI colors, yellow is positive and red is negative. Other color standards and probe suppliers may differ.

A quick practical TC polarity check:

1. Connect the thermocouple.
2. Read the thermocouple channel in RaceChrono.
3. Warm the thermocouple tip with your fingers, hot air, or a lighter from a safe distance.
4. If the temperature goes up, the polarity is correct.
5. If the temperature goes down or becomes negative, swap the two thermocouple wires.

Configuring The Thermocouple IC In Firmware

Edit Core/Inc/RaceTemp_config.h and set:

#define RACETEMP_THERMOCOUPLE_IC RACETEMP_THERMOCOUPLE_IC_MAX31855

or:

#define RACETEMP_THERMOCOUPLE_IC RACETEMP_THERMOCOUPLE_IC_MAX31856

For MAX31856, also select the thermocouple type:

#define RACETEMP_MAX31856_TC_TYPE RACETEMP_MAX31856_TC_TYPE_K

Available MAX31856 types are:

• RACETEMP_MAX31856_TC_TYPE_B
• RACETEMP_MAX31856_TC_TYPE_E
• RACETEMP_MAX31856_TC_TYPE_J
• RACETEMP_MAX31856_TC_TYPE_K
• RACETEMP_MAX31856_TC_TYPE_N
• RACETEMP_MAX31856_TC_TYPE_R
• RACETEMP_MAX31856_TC_TYPE_S
• RACETEMP_MAX31856_TC_TYPE_T

The firmware sends the thermocouple data as raw IC bytes on CAN ID 0x13. RaceChrono then decodes those bytes with an equation. This keeps the firmware simple and makes it possible to inspect status and fault bits from the IC.

Building

Open the project in STM32CubeMX and click "GENERATE CODE". This should generate some code files and copy some library files. See also my CubeMX-notes at the bottom of this page. Open the project in STM32CubeIDE and build the Debug or Release configuration.

The intended BLE security setup is:

• Bonding enabled
• No passkey
• No MITM requirement
• No input/output capability
• Secure connections optional

If pairing fails after a firmware or security setting change, delete/forget the old RaceTemp pairing on the phone and pair again.

Using With RaceChrono

1. Power the RaceTemp device.
2. Pair the phone with the BLE device named RaceTemp.
3. Open RaceChrono.
4. Add/connect it as a RaceChrono BLE DIY/CAN device.
5. Add custom CAN channels for the CAN IDs listed below.
6. Enable the channels you want to log.

RaceChrono may show CAN IDs in either hexadecimal or decimal form. For example, 0x13 is decimal 19.

RaceChrono equations are documented here:

https://racechrono.com/support/equations

The thermocouple equations below use RaceChrono's bitsToInt() function. In RaceChrono, bit offset 0 is the most significant bit of payload byte 0. For the MAX31855 and MAX31856 temperature channels, the recommended equations below use bytesToInt() because they are easier to enter correctly on a phone.

RaceChrono CAN Channels

Most RaceTemp channels are sent as little-endian 32-bit floats. For those channels, use this RaceChrono equation:

bytesToFloatLe(raw, 0, 4)

CAN ID	Decimal	Channel	Payload	Unit	RaceChrono equation
0x0B	11	MAP pressure	float32 little-endian	kPa	bytesToFloatLe(raw, 0, 4)
0x0C	12	MAP NTC temperature	float32 little-endian	deg C	bytesToFloatLe(raw, 0, 4)
0x0D	13	Volvo NTC temperature	float32 little-endian	deg C	bytesToFloatLe(raw, 0, 4)
0x0E	14	AC NTC temperature	float32 little-endian	deg C	bytesToFloatLe(raw, 0, 4)
0x0F	15	KOSO NTC temperature	float32 little-endian	deg C	bytesToFloatLe(raw, 0, 4)
0x10	16	STM32 MCU temperature	float32 little-endian	deg C	bytesToFloatLe(raw, 0, 4)
0x11	17	MAP raw ADC value	float32 little-endian	ADC count	bytesToFloatLe(raw, 0, 4)
0x12	18	NTC raw ADC value	float32 little-endian	ADC count	bytesToFloatLe(raw, 0, 4)
0x13	19	Thermocouple raw data	IC-specific raw bytes	deg C	See thermocouple sections below
0x14	20	Engine speed	float32 little-endian	RPM	bytesToFloatLe(raw, 0, 4)
0x15	21	Engine operating time	float32 little-endian	hours	bytesToFloatLe(raw, 0, 4)
0x16	22	Engine revolutions	float32 little-endian	rev	bytesToFloatLe(raw, 0, 4)
0x20	32	Raw measurement snapshot	packed raw bytes	debug	See source layout

Reading MAX31855 In RaceChrono

When RACETEMP_THERMOCOUPLE_IC_MAX31855 is selected, CAN ID 0x13 contains the four raw bytes read from the MAX31855. The byte order is the same as the IC SPI transfer: most significant byte first.

The MAX31855 thermocouple temperature is a signed 14-bit value with 0.25 deg C per bit.

Recommended RaceChrono equation:

bytesToInt(raw, 0, 2) / 16.0

Equivalent bitfield equation:

bitsToInt(raw, 0, 14) * 0.25

The bytesToInt() version works because the MAX31855 thermocouple value is left-aligned in the first two raw bytes.

Useful notes:

• The MAX31855 fault flag is bit D16 of the 32-bit raw value.
• The low bits contain the IC-specific fault details.
• A separate RaceChrono status channel can use bytesToUint(raw, 3, 1) to show the lowest raw byte.
• If the thermocouple channel shows unrealistic values, first confirm that the RaceTemp firmware is built for MAX31855 and not MAX31856.

Reading MAX31856 In RaceChrono

When RACETEMP_THERMOCOUPLE_IC_MAX31856 is selected, CAN ID 0x13 contains four bytes:

Payload byte	Contents
0	MAX31856 LTCBH register
1	MAX31856 LTCBM register
2	MAX31856 LTCBL register
3	MAX31856 fault/status register

The MAX31856 thermocouple temperature is a signed 19-bit value with 0.0078125 deg C per bit.

Recommended RaceChrono equation:

bytesToInt(raw, 0, 3) / 4096.0

Equivalent bitfield equation:

bitsToInt(raw, 0, 19) * 0.0078125

The bytesToInt() version works because the MAX31856 thermocouple value is left-aligned in the first three raw bytes.

Useful notes:

• Select the correct thermocouple type in RaceTemp_config.h.
• Payload byte 3 is the MAX31856 fault/status register.
• A separate RaceChrono status channel can use bytesToUint(raw, 3, 1).
• If the temperature is wrong but changes with heat, check the selected thermocouple type first.
• If the value is completely wrong, confirm that RaceChrono is using the MAX31856 equation and not the MAX31855 equation.

Raw Measurement Snapshot

CAN ID 0x20 is intended for development and debugging. It sends one packed snapshot of the raw measurement buffer:

• ADC samples
• Thermocouple SPI bytes
• Ignition timing data

Normal RaceChrono logging should usually use the individual channels instead. The raw snapshot is useful when checking new sensors or debugging conversion logic.

Notes About CubeMX Regeneration

Unfortunately the current version of CubeMX can make some mistakes (it can duplicate user-section content in the BLE files), so after regenerating the code, run the cleanup script before building:

powershell -ExecutionPolicy Bypass -File .\tools\fix-cubemx-ble-duplicates.ps1

The script removes duplicate CubeMX generated BLE functions and restores the BLE security settings used by this project.

To re-generate the code from CubeMX:

1. Open the .ioc file in CubeMX and click "GENERATE CODE"
2. Run tools/fix-cubemx-ble-duplicates.ps1
3. Build in STM32CubeIDE
4. Check that pairing still works with RaceTemp

Keep project-specific RaceTemp logic in the RaceTemp source files where possible. This reduces the amount of code that lives inside CubeMX user sections.