Serial Communication Protocol

Oct 13, 2025 by wbrum.org 136 views

Introduction

In this article, we will explore the issue of a watchdog triggered error when using a cheap yellow display with LVGL to create a simple multigauge. We will also discuss the problem of connecting to SAE1850 devices using the Bluetooth_multiple_pids example.

Background

The cheap yellow display is a popular choice for DIY projects due to its affordability and ease of use. However, it can be prone to issues such as watchdog triggered errors, which can be frustrating to debug.

The Issue

When using the Bluetooth_multiple_pids example, the serial monitor returns a "SEARCHING...UNABLE TO CONNECT" error message. This error occurs because the ELM327 chip in the SAE1850 device is not responding to the AT command.

Debugging the Issue

To debug this issue, we need to understand the communication protocol between the ELM327 chip and the microcontroller. The ELM327 chip uses a serial communication protocol to send and receive data.

Serial Communication Protocol

The serial communication protocol used by the ELM327 chip is a simple ASCII-based protocol. The microcontroller sends a command to the ELM327 chip, and the ELM327 chip responds with a response.

AT Command

The AT command is used to send a command to the ELM327 chip. The AT command is followed by a space and then the command. For example, the command to set the protocol to 0 would be "AT SP 0".

Debugging the AT Command

To debug the AT command, we need to understand the response from the ELM327 chip. The response from the ELM327 chip is a simple ASCII string that indicates the result of the command.

Response from ELM327 Chip

The response from the ELM327 chip is a string that indicates the result of the command. The response can be one of the following:

"OK" - The command was successful.
"ERROR" - The command failed.
"UNABLE TO CONNECT" - The ELM327 chip is not responding.

Debugging the Response

To debug the response from the ELM327 chip, we need to understand the ASCII string that is being sent. We can use a serial monitor to view the response from the ELM327 chip.

Serial Monitor

The serial monitor is a tool that allows us to view the serial communication between the microcontroller and the ELM327 chip. We can use the serial monitor to view the response from the ELM327 chip.

Debugging the Serial Monitor

To debug the serial monitor, we need to understand the ASCII string that is being sent. We can use a serial monitor to view the response from the ELM327 chip.

Conclusion

In conclusion, the watchdog triggered error when using a cheap yellow display with LVGL to create a simple multigauge is caused by a communication issue between the microcontroller and the ELM327 chip. The issue is caused by the ELM327 chip not responding to the AT command. To debug this issue, we need to understand the serial communication protocol used by the ELM327 chip and the response from the ELM327 chip.

Code

The code for this project is available on GitHub. The code uses the LVGL library to create a simple multigauge and the Bluetooth_multiple_pids example to connect to SAE1850 devices.

Code Snippet

void connect_to_obd() {
  update_status_label("Connecting to OBD...");
  SerialBT.begin("ESP32_OBD", true);
  //SerialBT.setTimeout(50);

  if (!SerialBT.connect("OBDII")) {
    update_status_label("Retrying OBD connection...");
    //vTaskDelay(pdMS_TO_TICKS(1000));
  }

  SerialBT.println("AT Z");     // Reset
  vTaskDelay(pdMS_TO_TICKS(1000));

  if (!obd.begin(SerialBT, true, 2000)) {
    update_status_label("Reinitializing ELM327...");
   // vTaskDelay(pdMS_TO_TICKS(200));
  }
  update_status_label("Connected to ELM327");
}

Code Explanation

The code snippet above is the connect_to_obd function, which is used to connect to SAE1850 devices using the Bluetooth_multiple_pids example. The function sends an AT command to the ELM327 chip to reset it, and then checks if the ELM327 chip is responding. If the ELM327 chip is not responding, the function retries the connection.

Code Debugging

To debug the code, we need to understand the serial communication protocol used by the ELM327 chip and the response from the ELM327 chip. We can use a serial monitor to view the response from the ELM327 chip.

Code Optimization

To optimize the code, we can use a more efficient serial communication protocol, such as the UART protocol. We can also use a more efficient algorithm to check if the ELM327 chip is responding.

Code Testing

To test the code, we need to connect the microcontroller to the ELM327 chip and the SAE1850 device. We can use a serial monitor to view the response from the ELM327 chip.

Code Conclusion

Q: What is a watchdog triggered error?

A: A watchdog triggered error is an error that occurs when a microcontroller's watchdog timer expires. The watchdog timer is a timer that is used to prevent a microcontroller from getting stuck in an infinite loop.

Q: What causes a watchdog triggered error?

A: A watchdog triggered error can be caused by a variety of factors, including:

A microcontroller getting stuck in an infinite loop
A microcontroller not responding to interrupts
A microcontroller not resetting the watchdog timer
A hardware issue with the microcontroller or its peripherals

Q: How can I prevent a watchdog triggered error?

A: To prevent a watchdog triggered error, you can:

Make sure that your microcontroller is not getting stuck in an infinite loop
Make sure that your microcontroller is responding to interrupts
Make sure that your microcontroller is resetting the watchdog timer regularly
Use a watchdog timer with a long timeout period
Use a watchdog timer with a reset function

Q: What is the difference between a watchdog timer and a reset function?

A: A watchdog timer is a timer that is used to prevent a microcontroller from getting stuck in an infinite loop. A reset function is a function that is used to reset a microcontroller to its default state.

Q: How can I debug a watchdog triggered error?

A: To debug a watchdog triggered error, you can:

Use a debugger to step through your code and see where the error is occurring
Use a serial monitor to view the output of your microcontroller
Use a logic analyzer to view the signals on your microcontroller's pins
Use a oscilloscope to view the signals on your microcontroller's pins

Q: What is the difference between a serial monitor and a logic analyzer?

A: A serial monitor is a tool that is used to view the output of a microcontroller. A logic analyzer is a tool that is used to view the signals on a microcontroller's pins.

Q: How can I optimize my code to prevent a watchdog triggered error?

A: To optimize your code to prevent a watchdog triggered error, you can:

Use a watchdog timer with a long timeout period
Use a watchdog timer with a reset function
Make sure that your microcontroller is not getting stuck in an infinite loop
Make sure that your microcontroller is responding to interrupts
Make sure that your microcontroller is resetting the watchdog timer regularly

Q: What is the difference between a watchdog timer and a reset function?

Q: How can I test my code to prevent a watchdog triggered error?

A: To test your code to prevent a watchdog triggered error, you can:

Use a debugger to step through your code and see where the error is occurring
Use a serial monitor to view the output of your microcontroller
Use a logic analyzer to view the signals on your microcontroller's pins
Use a oscilloscope to view the signals on your microcontroller's pins

Q: What is the difference between a serial monitor and a logic analyzer?

A: A serial monitor is a tool that is used to view the output of a microcontroller. A logic analyzer is a tool that is used to view the signals on a microcontroller's pins.

Q: How can I troubleshoot a watchdog triggered error?

A: To troubleshoot a watchdog triggered error, you can:

Use a debugger to step through your code and see where the error is occurring
Use a serial monitor to view the output of your microcontroller
Use a logic analyzer to view the signals on your microcontroller's pins
Use a oscilloscope to view the signals on your microcontroller's pins

Q: What is the difference between a serial monitor and a logic analyzer?

A: A serial monitor is a tool that is used to view the output of a microcontroller. A logic analyzer is a tool that is used to view the signals on a microcontroller's pins.

Q: How can I prevent a watchdog triggered error in my code?

A: To prevent a watchdog triggered error in your code, you can:

Use a watchdog timer with a long timeout period
Use a watchdog timer with a reset function
Make sure that your microcontroller is not getting stuck in an infinite loop
Make sure that your microcontroller is responding to interrupts
Make sure that your microcontroller is resetting the watchdog timer regularly