Rain-Sensor Wiper Controller - ESP32-P4

An ESP project that sits between Tesla's AP-computer and car, using a VAG rain/light sensor over LIN bus to automatically control wiper speed.

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Architecture

Rain/light sensor  ──LIN──►  ESP32-P4  ◄──CAN0──  AP-Computer ("car")
                           (magic here)
                                 │
                                 └──────CAN1──►  Actuator (wiper)

The ESP32-P4 acts as:

• LIN master - queries the Bosch/Continental VAG rain sensor (frame ID 0x21)
• CAN MITM gateway - intercepts the wiper control CAN frame, modifies it based on rain intensity, and forwards it to the car

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Hardware connections

Signal	ESP32-P4 GPIO	Connected to
CAN0 TX	GPIO 35	CAN transceiver 0 (car side)
CAN0 RX	GPIO 36	CAN transceiver 0
CAN1 TX	GPIO 31	CAN transceiver 1 (wiper side)
CAN1 RX	GPIO 34	CAN transceiver 1
LIN TX (UART1)	GPIO 20	LIN transceiver TX
LIN RX (UART1)	GPIO 21	LIN transceiver RX

Configure in main/config.h

Recommended ICs

• CAN transceivers: TJA1050, SN65HVD230, or MCP2551
• LIN transceiver: TJA1021, TJA1027, or MCP2003B
  (LIN transceiver handles the single-wire bus voltage; connect TX and RX to the same LIN pin on the transceiver)

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LIN break-field workaround

The ESP32 UART cannot natively emit a LIN break field (13+ dominant bits) because the hardware treats it as a UART error. The workaround (adapted from mestrode/Lin-Interface-Library) is to:

1. Drop baud rate to LIN_BAUD / 2 (9600 bps)
2. Transmit one 0x00 byte → produces ~20 dominant bits at nominal rate
3. Restore baud rate to LIN_BAUD (19200 bps)
4. Send sync byte 0x55 + protected ID
5. Flush the RX FIFO (single-wire echo) and read slave response

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VAG sensor protocol (LIN 2.x)

Byte	Field	Notes
0	Rain intensity	Lower nibble [3:0], range 0-15
1	Light intensity	0 = bright, 255 = very dark
2	Status flags	Sensor fault / init bits
3-6	Other channels	IR / solar / additional light data
7	Checksum	LIN 2.x enhanced (PID included)

Frame ID: 0x21 → Protected ID: 0x61

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Build

Git bash for Windows, terminal for macOS/Linux All env's use Dev Container for IDE

idf.sh build
idf.sh flash
idf.sh monitor

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File structure

wiper_controller/
├── CMakeLists.txt
└── main/
    ├── CMakeLists.txt
    ├── config.h          ← all pins, IDs, thresholds
    ├── main.c            ← startup, task creation
    ├── lin_sensor.h/.c   ← LIN master driver + break workaround
    ├── can_gateway.h/.c  ← dual TWAI MITM gateway
    └── wiper_logic.h/.c  ← rain→speed mapping + CAN frame encoding