MCU1 LED Control ECU (Arduino Uno + MCP2515)

This device drives an 8-LED strip over CAN and reports its current light status back to the Raspberry Pi 5 running the Kuksa CAN Provider.

Hardware

Component	Details
Board	Arduino Uno R4 WiFi
CAN transceiver	MCP2515 module (8 MHz crystal, TJA1050)
LED output	WS2812 LED strip (8 LEDs)
Bus	CAN at 500 kbit/s

See the Hardware BOM for sourcing details and wiring instructions.

Responsibilities

• Receive BlinkerCommand CAN frames from the Raspberry Pi 5
• Drive the WS2812 LED strip to show turn-indicator and brake-light states
• Send BlinkerStatus CAN frames reporting the current state back to the Pi

Arduino Libraries

• FastLED — WS2812 LED control
• 107-Arduino-MCP2515 — MCP2515 CAN controller driver

LED Allocation

LEDs 0–1, 3–4 and 6–7 drive the visible turn / brake functions. The two gap LEDs in between (indices 2 and 5) are reserved as CAN bus status / error indicators — they are dark in normal operation aside from a dim heartbeat and the colour-coded error patterns described below.

LEDs (1-based)	LEDs (0-based)	Function
1–2	0–1	Left indicator
3	2	CAN status indicator (heartbeat / RX blip / bus-fault)
4–5	3–4	Brake light
6	5	CAN error indicator (overrun / bad frame / bus-fault)
7–8	6–7	Right indicator

CAN Protocol

Payload Encoding

The Arduino expects a single-byte payload where each bit (or bit pair) represents a VSS signal. The same encoding is used when publishing status back to the Raspberry Pi.

Bit(s)	VSS Signal
0	Vehicle.Body.Lights.DirectionIndicator.Left.IsSignaling
1	Vehicle.Body.Lights.DirectionIndicator.Right.IsSignaling
2-3	Vehicle.Body.Lights.Brake.IsActive (0=INACTIVE, 1=ACTIVE, 2=ADAPTIVE)

CAN IDs

CAN ID	Name	Direction	Description
0x120 (288)	BlinkerCommand	Raspberry Pi → Arduino	Set blinker and brake state
0x121 (289)	BlinkerStatus	Arduino → Raspberry Pi	Report current state

See VSS / CAN Signal Mapping for the full DBC definition and value transforms.

LED Blinking Behavior

Signal State	LED Behavior
Left indicator ON	LEDs 0–1 blink at 1 Hz (500 ms on/off)
Right indicator ON	LEDs 6–7 blink at 1 Hz (500 ms on/off)
Brake ACTIVE	LEDs 3–4 solid on
All OFF	All function LEDs off (gap LEDs still show CAN status)

CAN Bus Status & Error Indication

The sketch polls the MCP2515 error flags (register EFLG, address 0x2D) every 200 ms and surfaces the result on the two gap LEDs. A quiet bus is not treated as an error — the kuksa-can-provider only transmits on signal change, so long idle periods between frames are normal.

Condition	LED 2 (status)	LED 5 (error)
Healthy / idle bus	Dim green heartbeat (0.5 Hz pulse)	Off
Valid BlinkerCommand (0x120) just received	Dim teal blip (250 ms)	Off
Software ring buffer full (frame dropped)	Dim green heartbeat	Yellow blink (latched ≥ 750 ms)
Bad frame received (wrong ID / zero length)	Dim green heartbeat	Purple blink (latched ≥ 750 ms)
Bus fault — MCP2515 reports bus-off or error-passive	Solid red	Solid red

A tiny 4-deep ring buffer absorbs back-to-back frames from the MCP2515's two hardware RX buffers, so the yellow "buffer overrun" LED only lights if loop() genuinely can't keep up.

Every error transition is also written to the serial console (115200 baud) so the operator can correlate the LEDs with the underlying cause:

[12350 ms] CAN error: BUS_FAULT (EFLG=0x20)
[13100 ms] CAN error: NONE
[15402 ms] CAN error: BAD_FRAME
[16155 ms] CAN error: NONE

The EFLG byte is included for BUS_FAULT and BUFFER_OVERRUN so the MCP2515 fault class (bus-off 0x20, TX error-passive 0x10, RX error-passive 0x08, RX overflow 0x40/0x80) is visible at a glance.

Wiring

MCP2515 to Arduino

MCP2515 Pin	Arduino Pin
VCC	5 V
GND	GND
CS	D10 (SPI SS)
SO	D12 (SPI MISO)
SI	D11 (SPI MOSI)
SCK	D13 (SPI SCK)
INT	D2

The WS2812 LED strip data line connects to a digital output pin (see sketch for the exact pin).

CAN Bus Connection

Connect CAN_H and CAN_L between the MCP2515 module and the Waveshare RS485 CAN Hat on the Raspberry Pi 5. Use twisted-pair wiring and add 120 Ω termination resistors at each end of the bus.

Configuration

• CAN bitrate: 500 kbit/s
• MCP2515 clock: 8 MHz

No Wi-Fi or MQTT configuration is needed — this ECU communicates solely over CAN.

Sketch Location

devices/mcu1-led-control-can/mcu1-led-control-can/mcu1-led-control-can.ino

Upload via the Arduino IDE (2.x) with the Arduino UNO R4 WiFi board selected.