How to: Tapping into CAN bus for light bar trigger

[QuickExploration]

1. Purpose
The goal of this project was to create a solution for controlling the lightbar in a 2020+ Ford Explorer using the vehicle's high beam signal. While a physical switch could have been used, it would have been inconvenient due to the limited number of unused spots within reach. To streamline the process, I chose to tap into the vehicle's CAN (Controller Area Network) bus, a communication system used in modern vehicles for exchanging data between electronic control units (ECUs). By doing so, I aimed to automate the activation and deactivation of the lightbar based on the high beam status, resulting in a more seamless experience.

In the Ford Explorer, headlight switching is controlled via a ground signal within the headlight assembly, making it nearly impossible to access the high beams directly without interacting with the vehicle's central computer system. This is where the CAN bus becomes essential: rather than trying to intercept physical signals, the high beam status is transmitted via CAN messages to various systems within the vehicle. These messages, when properly interpreted, can control external components such as the lightbar.

To interface with the CAN bus, I used an Arduino along with the MCP2515 CAN bus module. The Arduino handles the logic of monitoring CAN bus messages, processing the data, and triggering the lightbar activation. The MCP2515 acts as an external CAN controller, converting the physical CAN signals into a format that the Arduino can understand. Without the MCP2515, it would be impossible for the Arduino to communicate with the CAN bus, as most microcontrollers, like the Arduino, do not have built-in CAN functionality. This combination allowed me to capture the relevant CAN signals for the high beam status and control the lightbar accordingly.

By tapping into the CAN bus, I could bypass the physical limitations of the headlight assembly and interact with the vehicle's computer, creating an efficient and integrated solution for controlling the lightbar.

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[QuickExploration]

2. Approach

1. Initial Attempts:
To begin, I initially attempted to identify a direct method of controlling the lightbar using the high beams. My first strategy was to probe every wire leading into the headlights for a switching positive or ground, hoping to find a straightforward way to trigger the lightbar. Unfortunately, I did not find a suitable signal to control the lightbar. The headlight switching mechanism is controlled internally, with no accessible wiring directly corresponding to the high beam state. This meant that simply tapping into the headlight wiring would not work, and I needed to explore alternative solutions to interact with the vehicle’s electronic systems.

2. Attempt at Using OBD-II Port:
I moved to capturing CAN data through the vehicle’s OBD-II port, which I assumed would provide straightforward access to the vehicle's internal signals. However, this method quickly proved ineffective. The OBD-II gateway only relays data in response to specific requests, meaning it couldn’t supply the real-time information needed to monitor the high beam status. For applications like this lightbar, where the real-time state of the high beams is crucial, direct access to the CAN bus was necessary. This limitation led to a shift toward tapping into the CAN bus directly, bypassing the OBD-II port for more reliable and responsive data.

3. CAN Bus Access:
Access to the HS2 CAN bus can be established through the MCP2515 at the C140 Joint Connector, providing a reliable communication link with the vehicle's systems and ensuring the light bar powers on only when the vehicle is running. It's important to note that while my setup utilized specific CAN pins, such as VDB25 (CAN High) on pin 17 and VDB26 (CAN Low) on pin 18, connections may vary depending on the vehicle model. Look for a pair of twisted wires, which commonly represent CAN bus lines.

Spoiler: Why twisted wires?

The CAN bus lines are twisted to help reduce electrical noise and signal interference. Twisting the wires allows any electromagnetic noise that affects one wire to also affect the other equally, effectively canceling it out, which is critical for maintaining clean, reliable communication.

The following diagrams were supplied by Hutch555, big thanks to him!

Routing Diagram:
This routing diagram shows the layout of wire paths and connector locations in the vehicle's cabin. Key points like the C140 connector, where the CAN bus is accessed, and the C260 ground point are used for the circuit.

Pinout Diagram (CB140):
This diagram shows the pinout for C140, where we get access to the CAN bus and a convenient power source. VDB25 (CAN High) on pin 17, VDB26 (CAN Low) on pin 18, and CBB25 on pin 51.

4. Tapping the CAN bus:
I removed the trim on the passenger side to access the HS2 CAN wires. This process was straightforward with the correct wiring information. Once connected, the Arduino was able to sniff the CAN bus traffic. However, the overwhelming amount of data presented a challenge.

5. Data Filtering and Interpretation:
A significant challenge was managing the overwhelming CAN bus traffic. The Arduino struggled with filtering hexadecimal data, which made it difficult to isolate the high beam signal. To resolve this, I converted the data to decimal, which simplified the process and made the output easier for a human to read. This allowed me to identify the relevant CAN message IDs and focus on the high beam status, streamlining the debugging process. Without this approach, filtering and interpreting the data would have been far more difficult, given the constant flow of information.

6. Isolating data:
With the relevant CAN data identified (in decimal), I moved on to utilizing this information to control the lightbar. The key messages were:

Holding Brights: ID 131, Data: 64 32 0 0 12 150 0 0
Brights ON: ID 131, Data: 128 32 0 0 4 148 0 0
Brights OFF: ID 131, Data: 0 32 0 0 8 146 0 0

These messages provided the necessary data to configure the system to monitor the CAN bus. More details on how this data was processed will follow in the programming section.

 

[QuickExploration]

3. Circuitry

Power Regulation:
The system receives power from the vehicle’s electrical system, where the input voltage passes through a 220 µF capacitor before entering the LM2596 buck converter. This capacitor smooths out any voltage fluctuations to provide a stable input for the converter. The LM2596 steps down the voltage to a level suitable for the Arduino and other components.

Voltage Stabilization:
To ensure stable energy flow, an additional 0.1 µF capacitor is placed on the output side of the buck converter. This helps filter out high-frequency noise and ensures that the Arduino receives clean, stable voltage.

Arduino and CAN Bus Communication:
The output from the buck converter powers the Arduino, which is responsible for monitoring the vehicle's CAN bus via the MCP2515 CAN bus module. The Arduino processes the high beam signal by filtering and interpreting the CAN data.

MOSFET Control:
When the high beam signal is detected, the Arduino sends a signal to the IRL540N MOSFET. The control pin (pin 4) from the Arduino connects to the gate of the MOSFET through a 220-ohm resistor, which limits current to the gate and helps ensure reliable switching.

Gate Resistor:
A 10k-ohm resistor is placed between the gate and source of the MOSFET to stabilize the gate and prevent it from floating, ensuring that the MOSFET operates properly.

Lightbar Activation:
When the MOSFET is triggered by the Arduino, the drain of the MOSFET connects to the negative pole of the relay, energizing the coil, activating the lightbar when the high beams are on.

Spoiler: Justification for additional capacitors

While the LM2596 buck converter includes internal capacitors designed for basic filtering, I opted to add external capacitors for improved stability and noise reduction. The 220 µF capacitor placed at the input helps filter out any fluctuations or noise from the power supply, ensuring a stable voltage input for the converter. This is particularly important in automotive applications, where voltage spikes and drops are more common.

Wiring Details:
For connecting the Arduino to the MCP2515 CAN bus interface, the following pins were used:

• Arduino Pin 10 to CS (Chip Select)
• Arduino Pin 13 to SCK (Serial Clock)
• Arduino Pin 11 to SI (Serial Input)
• Arduino Pin 12 to SO (Serial Output)

GND and VCC connections were jumped from the Arduino to power the MCP2515.

I originally had the interrupt pin wired and included in the code, but ultimately decided against using it. The main loop checks the high beam status fast enough to activate the light bar without noticeable delay, making the interrupt unnecessary. You can disregard it in the wiring schematic.

Light Bar Harness and MOSFET Control:
For the light bar harness and MOSFET control, the grounding setup was modified for better control and functionality. Originally, the ground for the light bar, LED switch, and relay coil all shared the same ground path from the battery. To improve this, the ground connection for the relay coil and LED switch was rerouted through the MOSFET’s drain instead. This ensures that the LED switch's indicator only lights up when the MOSFET is activated.

The MOSFET’s drain is grounded through the vehicle's internal wiring, and when the MOSFET is triggered by the Arduino (via pin 4), it completes the circuit, allowing current to flow through the relay coil. The ground for the light bar itself, however, remains connected directly to the battery to ensure it has a stable return path, while the relay coil and LED switch ground are now handled by the MOSFET drain. This change prevents the LED switch from being illuminated when the system is powered off, and ensures that the light bar is only activated when the MOSFET is powered by the Arduino, which is controlled by the high beam signal.

Additionally, this setup allows for independent control of the high beams and light bar. If needed, the LED switch can be turned off by breaking the contact with the positive side of the relay coil, enabling the use of just the high beams without activating the light bar. This method provides a cleaner, more controlled way to manage both the high beams and light bar without unintended activation.

Flyback Diode Protection:
To protect the circuit from voltage spikes generated by the collapsing magnetic field of the relay coil, a 1N4007 flyback diode was placed across the relay. This diode, connected in reverse bias, allows the current from the spike to flow safely through the coil, preventing damage to sensitive components. The diode effectively absorbs the excess energy, preventing issues like arcing in the relay and protecting the MOSFET and Arduino from transients.

Circuit diagram:

 

[QuickExploration]

4. Programming​

The programming aspect of this project revolves around two key components: isolating the CAN bus signal related to the high beam status and activating the MOSFET to control the lightbar based on the high beam state. Below is an explanation of each code snippet, highlighting its functionality and things to watch out for when applying it to your own system.

Code to Isolate the Signal​

This snippet sets up the MCP2515 CAN bus interface to listen for incoming CAN messages to isolate the high beam signal based on the CAN ID.

Key Functions and Concepts:

• MCP_CAN mcp2515(10): This initializes the MCP2515 library with the chip select pin set to 10. Ensure this pin matches your physical wiring.
• mcp2515.begin(): Initializes the CAN bus communication. The parameters define the mode and baud rate of the communication, which may need adjustment depending on your specific vehicle's setup.
• mcp2515.checkReceive(): This function checks if a new CAN message has been received. If so, it proceeds to read the message.
• Serial.println(): Used for debugging, this prints out the CAN message ID and data in decimal format to the serial monitor. This helps you verify which IDs correspond to high beam status.

Things to Watch Out For:

• CAN bus traffic: Depending on the vehicle, CAN bus traffic can be overwhelming. The code prints all received data, which may include unnecessary messages. To handle this efficiently, you may want to add filtering based on the relevant CAN ID (in this case, 0x83 or 131 in decimal) as discussed earlier.
• Speed and Memory: The MCP2515 operates at a fixed baud rate, so make sure the settings match the vehicle's CAN bus. Also, serial printing can slow down processing, especially with a large amount of traffic. Keep this in mind while trying to isolate messages.

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Code to Activate the MOSFET​

This second snippet uses the high beam signal from the CAN bus to control the MOSFET, which in turn powers the lightbar. It checks if the CAN message contains the appropriate high beam data and then activates or deactivates the lightbar accordingly.

Key Functions and Concepts:

• CAN_ID and Filtering: The filtering process in the code helps optimize performance by ensuring that only relevant CAN bus messages are processed. The MCP2515 allows for hardware filtering, which means it can discard unwanted messages at the hardware level before they even reach the Arduino.
• Pin Setup: The LIGHTBAR_PIN (pin 4) controls the gate of the IRL540N MOSFET. When pin 4 is set HIGH (5V), the MOSFET allows current to power the lightbar. When pin 4 is LOW (0V), the MOSFET shuts off, turning the lightbar off. The 220-ohm resistor limits current to the MOSFET's gate, protecting the Arduino, while the 10k-ohm pull-down resistor ensures the MOSFET stays off when not driven. The IRL540N is chosen for its low gate threshold and efficient power handling, suitable for controlling the lightbar with the Arduino’s 5V logic.
• Byte Comparison: The code looks at specific bytes in the CAN message (byte 5 in this case) to determine if the high beams are on or off, using the previously identified data values for high beams (146 for off, 148 for on). I added in validation for the MOSFET to only trigger when the high beams are on and the stalk is no longer being used (buf[4] == VERIFY_BRIGHT).
• Serial Debugging: The debugging code, which prints received CAN messages to the serial monitor, is useful for development and troubleshooting. It helps verify that the Arduino is correctly receiving and processing the expected high beam data.

Things to Watch Out For:

• Pin Configuration: Ensure the pin defined as LIGHTBAR_PIN matches the physical pin used to control the MOSFET. If a different pin is used, adjust the code accordingly.
• CAN ID Matching: Double-check that the CAN ID 0x83 (or 131 decimal) corresponds to the high beam message for your specific vehicle. Depending on the manufacturer or vehicle model, the CAN ID or data structure might differ.
• Data Verification: The byte comparison (buf[5] == BRIGHT_OFF) checks the sixth byte in the CAN message. Ensure this aligns with the actual data being sent from your vehicle, as the data structure can vary across different car models.

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General Tips:​

• LISTENONLY Mode: The MCP2515 is run in LISTENONLY mode in both snippets to prevent interference with the CAN bus. This ensures the module only listens for messages and does not transmit anything that could cause conflicts. This is especially important when working with shared communication lines like the CAN bus.
• Serial Debugging: The Serial.print() and Serial.println() functions are crucial for debugging, but they should be removed during installation to reduce the computational load on the Arduino.
• Power Management: When dealing with MOSFETs and other components that control power, make sure to account for proper grounding and power flow to avoid damage to the components or the vehicle's electrical system.

By following these steps and keeping these considerations in mind, you'll be able to successfully isolate the relevant CAN bus data and use it to control your lightbar based on the high beam status.

 

[QuickExploration]

Code to identify the Signal​

#include <SPI.h>
#include <mcp_can.h>

MCP_CAN mcp2515(10);  // Set the CS pin for the MCP2515, adjust as necessary

void setup() {
    Serial.begin(115200);  // Start serial communication
    if (mcp2515.begin(MCP_STDEXT, CAN_500KBPS, MCP_8MHZ) == CAN_OK) {
        Serial.println("MCP2515 Initialized Successfully!");
    } else {
        Serial.println("MCP2515 Initialization Failed!");
        while (1);  // Stay in loop if initialization fails
    }
   
    mcp2515.setMode(MCP_NORMAL);  // Set the MCP2515 to normal mode
}

void loop() {
    // Check if a CAN message is available
    if (mcp2515.checkReceive() == CAN_MSGAVAIL) {
        unsigned char len = 0;  // Length of the received message
        unsigned char buf[8];   // CAN message buffer
        unsigned long id = 0;   // CAN message ID

        // Read the message from the CAN bus
        mcp2515.readMsgBuf(&id, &len, buf);

        // Print the CAN message ID
        Serial.print("CAN ID: ");
        Serial.println(id, HEX);  // Print the CAN ID in hexadecimal

        // Print the data of the message
        Serial.print("Data: ");
        for (int i = 0; i < len; i++) {
            Serial.print(buf[i], DEC);  // Print each byte in decimal
            Serial.print(" ");
        }
        Serial.println();  // Newline after each message
    }
}

 

[QuickExploration]

Code to activate the lightbar

#include <SPI.h>
#include <mcp_can.h>

MCP_CAN mcp2515(10);  // Set the CS pin for the MCP2515, adjust this if necessary
const int LIGHTBAR_PIN = 4; // Pin to control the MOSFET
const unsigned long CAN_ID = 0x83;  // CAN ID 0x83 corresponds to 131 decimal

// Define byte values for brights states
const byte BRIGHT_OFF = 146; // Brights are off (based on prior data)
const byte BRIGHT_ON = 148;  // Brights are on (based on prior data)
const byte VERIFY_BRIGHT = 4;

void setup() {
    Serial.begin(115200);  // Start serial communication
    pinMode(LIGHTBAR_PIN, OUTPUT);  // Set the lightbar (MOSFET) control pin as output
    digitalWrite(LIGHTBAR_PIN, LOW); // Ensure the lightbar is off at startup

    if (mcp2515.begin(MCP_STDEXT, CAN_500KBPS, MCP_8MHZ) == CAN_OK) {
        Serial.println("MCP2515 Initialized Successfully!");
    } else {
        Serial.println("MCP2515 Initialization Failed!");
        while (1);  // Stay in a loop if initialization fails
    }

    // Set the MCP2515 mode to normal for reading real CAN messages
    mcp2515.setMode(MCP_NORMAL);

    // Set up masks and filters to isolate CAN ID 0x83 (ID 131)
    mcp2515.init_Mask(0, 0x7FF);  // Initialize mask 0 for standard 11-bit IDs
    mcp2515.init_Filt(0, CAN_ID); // Filter for CAN ID 0x83
    mcp2515.init_Filt(1, CAN_ID); // Second filter for CAN ID 0x83
}

void loop() {
    // Check if a message is available on the CAN bus
    if (mcp2515.checkReceive() == CAN_MSGAVAIL) {
        unsigned char len = 0;      // Length of the received message
        unsigned char buf[8];       // CAN message buffer
        unsigned long id = 0;       // CAN message ID
        
        // Read the CAN message
        mcp2515.readMsgBuf(&id, &len, buf);

        // Process only the messages that match the filtered ID (0x83)
        if (id == CAN_ID) {
            // Check if the brights are ON or OFF using the sixth byte (buf[5])
            if (buf[5] == BRIGHT_OFF) {  // Brights are OFF
                Serial.println("Brights are OFF. Turning off the light bar.");
                digitalWrite(LIGHTBAR_PIN, LOW);  // Turn off the light bar (MOSFET off)
            } else if (buf[4] == VERIFY_BRIGHT && buf[5] == BRIGHT_ON) {  // Brights are ON
                Serial.println("Brights are ON. Turning on the light bar.");
                digitalWrite(LIGHTBAR_PIN, HIGH);  // Turn on the light bar (MOSFET on)
            }

            // Print the data for debugging purposes
            Serial.print("Data for ID 131 (0x83): ");
            for (int i = 0; i < len; i++) {
                Serial.print(buf[i], DEC);  // Print each byte in decimal
                Serial.print(" ");
            }
            Serial.println();
        }
    }
}

 

[QuickExploration]

5. PCB Enclosure

Once the software aspects of the project were resolved, the next step was to design a PCB enclosure that would fit neatly into the passenger-side footwell without occupying excessive space. After finalizing the PCB design, I moved to creating a 3D CAD file for the enclosure, with the ultimate goal of 3D printing it. This enclosure was essential for securely housing all the components, protecting them from the vehicle's environment, and ensuring that everything would be compact and easy to install.

The design process required careful consideration of both size and functionality. I needed to ensure that the PCB wouldn't interfere with existing vehicle controls while maintaining accessibility for future adjustments or troubleshooting. The goal was to create a practical, efficient solution that could be installed seamlessly in the Explorer without disrupting the vehicle's interior layout.

I am unable to link the CAD file for the enclosure, but you can message me, and I will send it your way. One thing to consider is that this file was made with my specific PCB dimensions in mind, so it will need adjustment if you plan to use it.

 

[QuickExploration]

6. Conclusion
This project was a fun exploration into integrating automotive systems with DIY electronics, specifically using an Arduino to control a lightbar based on the high beam status of the Ford Explorer. By tapping into the vehicle's HS2 CAN bus and utilizing an MCP2515 CAN controller, I was able to automate the lightbar's activation, removing the need for manual switching and improving convenience.

While automotive electronics may seem intimidating at first, this project has shown that anyone with an interest in electronics and coding can dive into something like this with the right tools and mindset. Looking ahead, I plan to integrate features like automatic sports mode activation on startup and disabling the auto stop-start function. This project holds even more potential than just controlling a light bar.

 

[Rick]

Thank you for tor the "how to".

I will set you up with an Elite membrership for your effort.