GPS Speedometer

Using Arduino Networking, Protocols, and Devices
1

Hello I'm using an Arduino UNO R4 with a Neo 7m Gps and an 8x32 Dot Matrix. I've spent some time on the code with little success so now im wondering what I need to do to fix my code.

2 
#include <SoftwareSerial.h>
#include <TinyGPS.h>
#include <MD_MAX72xx.h>
#include <SPI.h>

SoftwareSerial ss(4, 3);  // RX, TX pins for GPS (Software Serial)

TinyGPS gps;  // Create an instance of TinyGPS

#define DATA_PIN    11
#define CLOCK_PIN   13
#define LOAD_PIN    10
#define MAX_DEVICES 4  // 4 x 8x8 matrices = 32x8 display

// Initialize the MAX7219 with FC8_HW (for 8x8 matrix configuration)
MD_MAX72XX mx = MD_MAX72XX(MD_MAX72XX::FC16_HW, DATA_PIN, CLOCK_PIN, LOAD_PIN, MAX_DEVICES);

// Digit patterns (8x8 matrix for digits 0-9)
const uint8_t digitPatterns[10][8] = {
  {0x7E, 0x09, 0x09, 0x09, 0x7E, 0x00, 0x00, 0x00}, // 0
  {0x00, 0x00, 0x0F, 0x00, 0x00, 0x00, 0x00, 0x00}, // 1
  {0x7E, 0x01, 0x7E, 0x40, 0x7E, 0x00, 0x00, 0x00}, // 2
  {0x7E, 0x01, 0x7E, 0x01, 0x7E, 0x00, 0x00, 0x00}, // 3
  {0x7E, 0x40, 0x7E, 0x01, 0x01, 0x00, 0x00, 0x00}, // 4
  {0x7E, 0x40, 0x7E, 0x01, 0x7E, 0x00, 0x00, 0x00}, // 5
  {0x7E, 0x40, 0x7E, 0x49, 0x7E, 0x00, 0x00, 0x00}, // 6
  {0x7E, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00}, // 7
  {0x7E, 0x49, 0x7E, 0x49, 0x7E, 0x00, 0x00, 0x00}, // 8
  {0x7E, 0x49, 0x7E, 0x01, 0x7E, 0x00, 0x00, 0x00}  // 9
};

void setup() {
  // Start serial communication for debugging
  Serial.begin(115200);
  ss.begin(9600);  // GPS Serial

  // Initialize MAX7219
  mx.begin();
  mx.clear();  // Clear the display initially
  delay(500);  // Give time for hardware to initialize

  // Set the intensity of all devices to a reasonable level (e.g., intensity 5)
  for (int i = 0; i < MAX_DEVICES; i++) {
    mx.control(i, MD_MAX72XX::INTENSITY, 5);  // Set intensity to 5 (out of 15)
  }

  Serial.println("MAX7219 Initialized");

  // Initialize GPS
  // GPS setup can be handled in the loop by continuously reading GPS data
}

void loop() {
  // Read GPS data
  while (ss.available() > 0) {
    gps.encode(ss.read());
  }

  // Check if new GPS data is available and valid
  float latitude, longitude;
  float speed;

  // Retrieve latitude, longitude, and speed
  gps.f_get_position(&latitude, &longitude);
  speed = gps.speed();  // Speed in km/h

  // If valid GPS data is available
  if (latitude != TinyGPS::GPS_INVALID_ANGLE && longitude != TinyGPS::GPS_INVALID_ANGLE) {
    // Convert speed from km/h to mph
    float speedMPH = speed * 0.621371;
    displaySpeed(round(speedMPH));  // Round speed for display
  } else {
    displayMessage("Waiting for Fix");
  }

  delay(1000);  // Delay between updates
}

// Function to display speed on the MAX7219
void displaySpeed(float speed) {
  mx.clear();  // Clear the display first

  // Convert speed to an integer
  int speedInt = int(speed);
  String speedStr = String(speedInt);

  // If speed is more than 9999, just display the last four digits
  if (speedInt > 9999) {
    speedStr = String(speedInt).substring(speedStr.length() - 4);
  }

  // Display each digit (speedStr should contain the string representation of the speed)
  for (int i = 0; i < speedStr.length(); i++) {
    char digitChar = speedStr[i];  // Get the digit as a character
    int digit = digitChar - '0';   // Convert char to int (0–9)

    // Display the digit on the corresponding position on the matrix
    displayDigit(i * 8, digit);  // Display at the correct X position
  }

  // Update the display
  mx.update();
}

// Function to display an individual digit (8x8 matrix)
void displayDigit(int xOffset, int digit) {
  for (int row = 0; row < 8; row++) {
    uint8_t rowData = digitPatterns[digit][row]; // Get the row data for the digit
    for (int col = 0; col < 8; col++) {
      // Set each point on the display based on the rowData (1 = LED on, 0 = LED off)
      bool isOn = (rowData & (1 << (7 - col))) > 0; // Check if the LED should be on
      mx.setPoint(xOffset + col, row, isOn);       // Set the point on the matrix
    }
  }
}

// Function to display a custom message on the matrix
void displayMessage(String message) {
  int messageLength = message.length();
  int startX = 0;

  // Scroll the message across the matrix
  for (int i = 0; i < messageLength; i++) {
    char ch = message[i];
    
    // Find the corresponding digit pattern for the character
    int charIndex = ch - '0';  // This assumes the message only contains digits, modify if using letters.
    
    if (ch == ' ') {
      charIndex = -1; // Treat space as an empty pattern
    }

    // Display the character on the matrix at the current offset
    if (charIndex != -1) {
      for (int row = 0; row < 8; row++) {
        uint8_t rowData = digitPatterns[charIndex][row];
        for (int col = 0; col < 8; col++) {
          bool isOn = (rowData & (1 << (7 - col))) > 0;
          mx.setPoint(startX + col, row, isOn);
        }
      }
    }
    
    // Wait for a small amount of time to simulate scrolling
    delay(300);
    
    // Clear the matrix for the next character
    mx.clear();
    startX += 8;
  }
}
3

Believe it or not! You actually need to write down what you need to fix, We do not read minds, here.

4

Was this sketch perhaps generated by ChatGPT or one of its cousins?

5

It’s was not

6

I added the code

7

And be so kind to tell us what you think needs fixing.