4.6 Card Recognition

4.6.1 Algorithm

It can identify whether there are corresponding traffic cards in the image. If yes, it will return information including the coordinates, size, and label values of the cards.

4.6.2 Classification Label

Label	Definition	Pic
1	go forward
2	turn left
3	turn right
4	turn around
5	stop
6	green light
7	red light
8	speed 40
9	speed 60
10	speed 80

Note: The algorithm can recognize multiple cards simultaneously. The card can still be recognized within a certain rotation, deflection and pitch angle. When using, please make the card face the camera as directly as possible for better recognition effect.

4.6.3 Returned Values

When the controller acquires the recognition result, the algorithm will return the followings:

Parameter	Definition
kXValue	Card central coordinate x
kYValue	Card central coordinate y
kWidthValue	Card width w
kHeightValue	Card height h
kLabel	Card label value

Code:

   // Traverse all the detected cards
    for (int i = 1; i <= obj_num; ++i) {
      // Obtain the coordinate and size of the card in the image
      int x = sengo.GetValue(VISION_TYPE, kXValue, i);      // Card central coordinate x
      int y = sengo.GetValue(VISION_TYPE, kYValue, i);      // Card central coordinate y
      int w = sengo.GetValue(VISION_TYPE, kWidthValue, i);  // Card width
      int h = sengo.GetValue(VISION_TYPE, kHeightValue, i); // Card height
      
      // Card label value (Corresponding to the card_classes array index)
      int card_type = sengo.GetValue(VISION_TYPE, kLabel, i);
      
      // Ensure that the card type is within a valid range (to prevent array out-of-bounds)
      if (card_type < 0) card_type = 0;
      if (card_type >= sizeof(card_classes)/sizeof(card_classes[0])) 
        card_type = 0;
      
      // Print the detailed information of the card
      Serial.print("  Card #");
      Serial.print(i);
      Serial.print(": ");
      Serial.print("Position=(");
      Serial.print(x);
      Serial.print(",");
      Serial.print(y);
      Serial.print("), Size=");
      Serial.print(w);
      Serial.print("x");
      Serial.print(h);
      Serial.print(", Type=");
      Serial.println(card_classes[card_type]);  // Use the mapping table to obtain the type name
    }

4.6.4 Test Code

#include <Arduino.h>          // Arduino core library
#include <Sentry.h>           // Sentry machine vision sensor library

// Create an alias Sengo for the Sengo2 type to simplify subsequent usage
typedef Sengo2 Sengo;

// Communication method (currently enabled I2C).
#define SENGO_I2C             
// #define SENGO_UART         // UART serial communication solution (annotated as disabled)

// Include the corresponding library according to the selected communication mode
#ifdef SENGO_I2C
#include <Wire.h>             // Libraries required for I2C communication
#endif

#ifdef SENGO_UART
#include <SoftwareSerial.h>   // Soft serial library
#define TX_PIN 11  // Customize the TX pin
#define RX_PIN 10  // Customize the RX pin
SoftwareSerial mySerial(RX_PIN, TX_PIN);  // Create a soft serial port object
#endif

// Define the visual processing type as a machine card recognition mode
#define VISION_TYPE Sengo::kVisionCard  

// Create a Sengo sensor object
Sengo sengo;

// Card type name mapping table (Index corresponding to card label values)
const char* card_classes[] = {
  "unknown",      // 0: Unknown card type
  "forward",      // 1: Forward
  "left",         // 2: Turn left
  "right",        // 3: Turn right
  "turn_around",  // 4: Turn around
  "park",         // 5: Stop
  // Note: The size of the array should match the actual number of card types
};

void setup() {
  sentry_err_t err = SENTRY_OK;  // Define the error state variable and initialize it to be error-free

  Serial.begin(9600);            // Initialize the serial port for debugging the output
  Serial.println("Waiting for sengo initialize...");  // Print the initialization prompt

// Initialize the sensor according to the selected communication mode
#ifdef SENGO_I2C
  Wire.begin();  // Initialize the I2C bus
  // Keep trying to connect until succeed
  while (SENTRY_OK != sengo.begin(&Wire)) { 
    yield();  // Allow other tasks to run while waiting
  }
#endif  // SENGO_I2C

#ifdef SENGO_UART
  mySerial.begin(9600);           // Initialize the soft serial port with a baud rate of 9600
  // Keep trying to connect until succeed
  while (SENTRY_OK != sengo.begin(&mySerial)) { 
    yield();  // Allow other tasks to run while waiting
  }
#endif  // SENGO_UART

  Serial.println("Sengo begin Success.");  // Print the successful initialization information of the sensor
  
  // Activate the machine card recognition function
  err = sengo.VisionBegin(VISION_TYPE);
  
  // Print the initialization result of c recognition
  Serial.print("sengo.VisionBegin(kVisionCard) ");
  if (err) {
    Serial.print("Error: 0x");    // If an error occurs, print the error prefix
  } else {
    Serial.print("Success: 0x");  // If successful, print the success prefix
  }
  Serial.println(err, HEX);       // Print the error code in hexadecimal format
}

void loop() {
  // Obtain the number of detected cards (kStatus returns the total number of detected cards)
  int obj_num = sengo.GetValue(VISION_TYPE, kStatus);
  
  // If at least one card is detected
  if (obj_num > 0) {
    // Print the total number of detected cards
    Serial.print("Totally ");
    Serial.print(obj_num);
    Serial.println(" cards detected");
    
   // Traverse all the detected cards
    for (int i = 1; i <= obj_num; ++i) {
      // Obtain the coordinate and size of the card in the image
      int x = sengo.GetValue(VISION_TYPE, kXValue, i);      // Card central coordinate x
      int y = sengo.GetValue(VISION_TYPE, kYValue, i);      // Card central coordinate y
      int w = sengo.GetValue(VISION_TYPE, kWidthValue, i);  // Card width
      int h = sengo.GetValue(VISION_TYPE, kHeightValue, i); // Card height
      
      // Card label value (Corresponding to the card_classes array index)
      int card_type = sengo.GetValue(VISION_TYPE, kLabel, i);
      
      // Ensure that the card type is within a valid range (to prevent array out-of-bounds)
      if (card_type < 0) card_type = 0;
      if (card_type >= sizeof(card_classes)/sizeof(card_classes[0])) 
        card_type = 0;
      
      // Print the detailed information of the card
      Serial.print("  Card #");
      Serial.print(i);
      Serial.print(": ");
      Serial.print("Position=(");
      Serial.print(x);
      Serial.print(",");
      Serial.print(y);
      Serial.print("), Size=");
      Serial.print(w);
      Serial.print("x");
      Serial.print(h);
      Serial.print(", Type=");
      Serial.println(card_classes[card_type]);  // Use the mapping table to obtain the type name
    }
  }
  
  delay(200);
}

4.6.5 Test Result

After uploading the code, the AI vision module will scan the area captured by the camera. If there is a card, it will recognize the card and print its type (forward, turn around, turn left, turn right, etc.) in the serial monitor.

4.6.6 Extension Gameplay

Color picker

Game rule: Rotate the card (to the right/left) to change WS2812 light colors. For example, the normal sequence of lights is: red > green > blue > yellow > purple, etc., yet we can adjust them by turning the card. Suppose the current color is red, and we rotate the card to the right to change it to green; rotate to the left to make it purple; in a loop.
Practice: After identifying the card, control the light by performing addition or subtraction on a variable.