Exercise 3: Ultrasonic Distance Measurement

Lesson Plan: Ultrasonic Distance Measurement and Echo Analysis

Lesson Objectives:

1. Understand how ultrasonic sensors work for distance measurement.
2. Learn how to trigger and read data from an ultrasonic sensor using Arduino.
3. Use Red Pitaya to visualize and analyze the echo signal, focusing on amplitude, timing, and noise.

Lesson Outline:

1. Introduction

• Topic Overview:
• Ultrasonic sensors measure distance by emitting high-frequency sound waves and timing the echo return.
• Key concepts include the speed of sound, trigger signals, echo response, and the relationship between echo time and distance.
• Why It Matters:
• Ultrasonic sensors are widely used in robotics, automation, and obstacle detection. Understanding their operation and signal characteristics is essential for implementing reliable distance measurement systems.

2. Hardware Setup

A. Components:

• Ultrasonic Sensor (HC-SR04 or equivalent):A sensor that measures distance using ultrasonic waves.
• 10 kΩ Resistor (Optional):For signal conditioning, if needed.
• Arduino Uno
• Red Pitaya STEMlab 125-14

B. Circuit Assembly:

1. Connect the Ultrasonic Sensor:
• VCC to Arduino 5V.
• GND to Arduino GND.
• Trigger Pin to Arduino digital pin (e.g., pin 9).
• Echo Pin to Arduino digital pin (e.g., pin 10).
2. For signal analysis with Red Pitaya:
• Connect the Echo Pin to Red Pitaya IN1 to capture the echo signal.

3. Arduino Programming: Reading Distance Data

A. Basic Distance Measurement:

1. Write a sketch to calculate distance using the HC-SR04 sensor.
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const int trigPin = 9;
const int echoPin = 10;

void setup() {
    pinMode(trigPin, OUTPUT);
    pinMode(echoPin, INPUT);
    Serial.begin(9600);
}

void loop() {
    // Send trigger pulse
    digitalWrite(trigPin, LOW);
    delayMicroseconds(2);
    digitalWrite(trigPin, HIGH);
    delayMicroseconds(10);
    digitalWrite(trigPin, LOW);

    // Measure echo pulse duration
    long duration = pulseIn(echoPin, HIGH);

    // Calculate distance (cm)
    long distance = duration * 0.034 / 2;

    Serial.print("Distance: ");
    Serial.print(distance);
    Serial.println(" cm");
    delay(500);
}

2. Upload the sketch to Arduino and observe distance readings in the serial monitor.

4. Signal Analysis with Red Pitaya

A. Connecting Red Pitaya:

1. Connect the Echo Pin to Red Pitaya IN1 to capture the raw signal.
2. Ensure the GND of the Red Pitaya is connected to the Arduino’s GND.

B. Visualizing the Echo Signal:

1. Open the Red Pitaya oscilloscope tool.
2. Configure the input channel for a range of 0–5V.
3. Observe the echo signal:
• Identify the trigger pulse and the returning echo.
• Measure the time delay between the trigger and echo signals.

C. Analyzing Signal Characteristics:

1. Analyze the amplitude of the echo signal to determine how it weakens with increasing distance.
2. Measure the timing of the echo signal and verify it matches the distance calculated by Arduino.
3. Identify any noise or interference in the signal and discuss potential causes (e.g., environmental factors).

5. Analysis and Insights

A. Understanding Echo Response:

• Explain how the echo signal corresponds to distance.
• Discuss the effects of surface material, angle, and size on echo strength.

B. Observing Signal Noise:

• Highlight sources of noise in the environment (e.g., reflections from nearby objects).
• Discuss how noise affects the accuracy of distance measurements.

C. Improving Signal Quality:

• Suggest hardware solutions, such as shielding or adding resistors, to minimize noise.
• Discuss software techniques, such as averaging multiple readings, to improve reliability.

6. Wrap-Up and Discussion

• Key Takeaways:
1. Ultrasonic sensors rely on accurate timing and clean signals for precise distance measurements.
2. Arduino provides basic distance calculations, while Red Pitaya allows for in-depth analysis of echo signals.
3. Analyzing signal characteristics helps identify and mitigate issues like noise and weak echoes.
• Real-World Applications:
• Discuss the use of ultrasonic sensors in robotics, automotive parking systems, and industrial automation.

Homework/Extra Work

1. Experiment with different target materials and distances to observe changes in the echo signal.
2. Use Red Pitaya’s signal generator to create interference and analyze its impact on the echo signal.