CAN integration notes

Hardware Overview

Your ECU
    │ CANH / CANL
    ▼
Adafruit CAN Pal (TJA1051T/3)
    │ CTX → ESP32 GPIO 22 (TWAI TX)
    │ CRX → ESP32 GPIO 21 (TWAI RX)
    │ VCC → 5V
    │ GND → GND
    ▼
ESP32 TWAI controller

CAN Pal (TJA1051T/3) Notes

• 5V supply rail (connect to board 5V)
• 3.3V logic compatible on TX/RX — ESP32 GPIO is directly compatible
• Supports up to 1 Mbps
• Integrated wake-up filter
• TXD dominant timeout protection (prevents bus lock if ESP32 hangs)

Termination

• A CAN bus requires exactly two 120 Ω termination resistors, one at each end
• Check your ECU’s documentation — some have internal termination, some don’t
• The CAN Pal does NOT include termination — add a 120 Ω resistor on its CANH-CANL pins if needed
• Short stubs (<30 cm) typically work without extra termination

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Signal Mapping

Important

The frame IDs and byte positions in signals.json are examples. Verify them against your ECU’s CAN output configuration before use.

How to verify:

1. Use Studio’s CAN Scanner tab — connect the display while the ECU is running
2. Capture live frames: note which IDs appear and at what rate
3. Cross-reference with your ECU’s documentation or configuration software
4. Update signals.json to match, then push from Studio

Example Frame Layout (edit to match your ECU)

Frame ID	Example content
0x370	RPM, TPS, MAP, IAT, Speed
0x371	Lambda, Gear, Fuel pressure
0x372	Coolant temp, Oil temp, Oil pressure
0x373	Battery voltage
0x374	Status flags (MIL, launch, etc.)
0x375	Map number / profile

CAN Speed

Default: 500 kbps — configurable in signals.json (canSpeedKbps) and Studio → Device Config. Common ECU values: 500 kbps, 1 Mbps. Verify in your ECU’s configuration.

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Update Rates

Different signals typically update at different rates. Set timeoutMs in signals.json to at least 3× the expected update period to avoid false “signal lost” warnings.

Signal category	Typical update rate
RPM, TPS, MAP	10 ms (100 Hz)
Speed, Lambda	20 ms (50 Hz)
Temperatures	100 ms (10 Hz)
Oil pressure	50 ms (20 Hz)
Flags / status	100 ms (10 Hz)

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Signal Smoothing Strategy

Gauges (RPM, boost, oil pressure) use EMA (Exponential Moving Average) smoothing to prevent LVGL widget jitter from high-frequency signal noise:

smoothed = α × raw + (1 - α) × smoothed

Where α = SIGNAL_EMA_ALPHA = 0.2 (from app_config.h).

• Lower α = more smoothing (slower response to sudden changes)
• Higher α = less smoothing (faster response, more jitter)

Labels showing temperature, voltage, gear use raw values (no smoothing needed).

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Diagnostics

CAN health can be monitored via the USB serial console:

[I][CAN] TWAI driver started successfully
[I][CAN] Frame count: 1234
[W][CAN] TWAI receive error: ESP_ERR_TIMEOUT
[E][CAN] TWAI bus-off — attempting recovery

If you see constant timeout errors:

1. Check CAN speed matches ECU setting
2. Check CANH/CANL wiring (not swapped)
3. Check termination
4. Confirm ECU CAN output is enabled

If you see bus-off errors:

1. Check for wiring short
2. Check for ground loop between ECU and display power

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Known Risks

1. Frame IDs unverified — signals.json contains example frame IDs. If wrong, CAN data will be silently ignored. Always verify with Studio’s CAN Scanner.

2. TWAI pin conflict — GPIO 22 and 21 must not be used by SPI or other peripherals. Verify against board_config.h and CrowPanel 2.8” schematic.

3. CAN ground — ensure a common ground between ECU, CAN Pal, and ESP32. Poor grounding causes signal integrity issues and CRC errors.

4. Noise — in a car environment, CAN bus noise is common. Use twisted pair for CANH/CANL wiring. Keep CAN cable away from ignition wiring.