How to Use QTR-8A Reflectance Sensor Array: Examples, Pinouts, and Specs

The QTR-8A Reflectance Sensor Array by Pololu is an array of 8 reflectance sensors designed for line following and edge detection in robotics. Each sensor in the array provides an analog output that corresponds to the reflectance of the surface beneath it. This makes the QTR-8A ideal for applications such as line-following robots, edge detection, and other robotics projects that require surface reflectance measurements.

• Manufacturer: Pololu
• Part ID: QTR-8A
• Number of Sensors: 8
• Operating Voltage: 3.3V to 5V
• Current Consumption: 100 mA (typical)
• Output Type: Analog
• Sensor Type: Infrared reflectance sensor
• Dimensions: 75mm x 10mm x 3mm
• Weight: 3.09g

1. Power Supply: Connect the VCC pin to a 3.3V or 5V power supply and the GND pin to the ground of your circuit.
2. Analog Outputs: Connect the OUT0 to OUT7 pins to the analog input pins of your microcontroller (e.g., Arduino).
3. LED Control: Connect the LEDON pin to a digital output pin of your microcontroller to control the IR LEDs. Pulling this pin low will turn the LEDs on.

- VCC -> 5V (Arduino)
- GND -> GND (Arduino)
- OUT0 -> A0 (Arduino)
- OUT1 -> A1 (Arduino)
- OUT2 -> A2 (Arduino)
- OUT3 -> A3 (Arduino)
- OUT4 -> A4 (Arduino)
- OUT5 -> A5 (Arduino)
- OUT6 -> A6 (Arduino)
- OUT7 -> A7 (Arduino)
- LEDON -> D2 (Arduino)

• Power Supply: Ensure that the power supply voltage matches the operating voltage range of the sensor array (3.3V to 5V).
• Analog Readings: Use the analogRead() function in Arduino to read the analog values from the sensor outputs.
• LED Control: Use a digital pin to control the LEDON pin. Pulling it low will turn the IR LEDs on, which is necessary for the sensors to function correctly.

// Define the pins for the sensor outputs and LED control
const int sensorPins[8] = {A0, A1, A2, A3, A4, A5, A6, A7};
const int ledPin = 2;

void setup() {
  // Initialize serial communication for debugging
  Serial.begin(9600);
  
  // Set the LED control pin as output
  pinMode(ledPin, OUTPUT);
  
  // Turn on the IR LEDs
  digitalWrite(ledPin, LOW);
}

void loop() {
  // Read and print the sensor values
  for (int i = 0; i < 8; i++) {
    int sensorValue = analogRead(sensorPins[i]);
    Serial.print("Sensor ");
    Serial.print(i);
    Serial.print(": ");
    Serial.println(sensorValue);
  }
  
  // Add a small delay to avoid flooding the serial monitor
  delay(100);
}

1. No Output from Sensors:

   • Solution: Ensure that the VCC and GND pins are connected correctly. Check if the LEDON pin is pulled low to turn on the IR LEDs.

2. Inconsistent Readings:

   • Solution: Ensure that the sensor array is positioned correctly over the surface. Check for any obstructions or reflective surfaces that might interfere with the readings.

3. High Power Consumption:

   • Solution: Verify that the power supply can provide sufficient current (100 mA typical). If using a battery, ensure it is fully charged.

• Check Connections: Double-check all connections to ensure they are secure and correct.
• Calibrate Sensors: If readings are inconsistent, consider calibrating the sensors by taking multiple readings and averaging them.
• Use Proper Surfaces: Ensure that the surface being detected is suitable for reflectance measurements (e.g., white lines on a dark background for line following).

By following this documentation, users should be able to effectively integrate and utilize the QTR-8A Reflectance Sensor Array in their robotics projects.