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6.1 Measuring Distance with an Ultrasonic Sensor

In this lesson, we’ll learn how to use an ultrasonic sensor module with the Raspberry Pi Pico 2 W to measure the distance to an object. Ultrasonic sensors are commonly used in robotics and automation systems for object detection and distance measurement.

Ultrasonic Module

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	PURCHASE LINK
Pico 2 W Starter Kit	450+	Pico 2 W Kit

You can also buy them separately from the links below.

SN	COMPONENT INTRODUCTION	QUANTITY	PURCHASE LINK
1	Getting to Know Pico 2 W	1
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	Ultrasonic Module	1	BUY

Understanding the Ultrasonic Sensor

The ultrasonic sensor works by emitting a short ultrasonic pulse from the Trig pin and listening for the echo on the Echo pin. By measuring the time it takes for the echo to return, we can calculate the distance to an object using the speed of sound.

Trigger Pulse: A 10-microsecond high pulse on the Trig pin initiates the measurement.
Ultrasonic Burst: The sensor emits an 8-cycle ultrasonic burst at 40 kHz.
Echo Reception: The Echo pin goes high, and stays high until the echo is received back.
Time Measurement: By measuring the time the Echo pin stays high, we can calculate the distance.

Schematic

sch_ultrasonic

Wiring

wiring_ultrasonic

Writing the Code

We’ll write a program that triggers the ultrasonic sensor, measures the echo time, and calculates the distance to an object. The distance will be printed to the Serial Monitor.

Note

You can open the file 6.1_ultrasonic.ino under the path of pico-2w-kit-main/arduino/6.1_ultrasonic.
Or copy this code into Arduino IDE.
Don’t forget to select the board(Raspberry Pi Pico) and the correct port before clicking the Upload button.

// Define the connection pins
const int trigPin = 17;  // GPIO 17 -> Trig
const int echoPin = 16;  // GPIO 16 -> Echo

void setup() {
  // Initialize serial communication at 115200 baud
  Serial.begin(115200);

  // Initialize the sensor pins
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  long duration;
  float distance;

  // Trigger the sensor by setting Trig HIGH for 10 microseconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the Echo pin, returns the duration in microseconds
  duration = pulseIn(echoPin, HIGH);

  // Calculate the distance in centimeters
  distance = duration * 0.034 / 2;

  // Print the distance to the Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  delay(500); // Wait for half a second before the next measurement
}

After uploading the code, the Serial Monitor should display the distance measurements in centimeters.

Distance: 25.3 cm
Distance: 24.8 cm
Distance: 24.5 cm

Place an object at varying distances from the sensor. Move the object closer and farther to observe changes in the distance readings.

Understanding the Code

Defining Connection Pins:
- trigPin: Sends the ultrasonic pulse.
- echoPin: Receives the echo of the ultrasonic pulse.
```
const int trigPin = 17;  // GPIO 17 -> Trig
const int echoPin = 16;  // GPIO 16 -> Echo
```

Setup Function:

Serial Communication: Enables communication between the Pico and the computer for debugging.
Pin Modes: Sets the Trig pin as OUTPUT and the Echo pin as INPUT.

void setup() {
  // Initialize serial communication at 115200 baud
  Serial.begin(115200);

  // Initialize the sensor pins
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

Loop Function:
- Triggering the Sensor: Sets the Trig pin HIGH for 10 microseconds to send the ultrasonic pulse. Sets the Trig pin LOW to end the pulse.
```
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
```
- Reading the Echo: Measures the duration (in microseconds) that the Echo pin stays HIGH, indicating the time taken for the echo to return.
```
duration = pulseIn(echoPin, HIGH);
```
- Calculating Distance: Converts the time to distance (cm/microsecond). Divides by 2 to account for the round-trip of the pulse.
```
distance = duration * 0.034 / 2;
```
- Serial Output: Prints the calculated distance to the Serial Monitor for real-time monitoring.
```
Serial.print("Distance: ");
Serial.print(distance);
Serial.println(" cm");
```
- Delay: Adds a 500-millisecond delay to prevent flooding the Serial Monitor and to allow time between measurements.

Troubleshooting

No Readings Displayed:
- Ensure the Trig and Echo pins are correctly connected.
- Verify that the sensor is receiving power (VCC and GND connections).
- Check that the Serial Monitor is set to the correct baud rate.
Incorrect Readings:
- Ensure that the calculations in the code are correct.
- Verify that the speed of sound constant (0.034) is appropriate for your environment (humidity and temperature can affect sound speed).
Sensor Interference:
- Make sure there are no obstructions or reflective surfaces that might interfere with the ultrasonic pulses.
- Avoid placing the sensor near other ultrasonic devices that could cause false readings.

Further Exploration

Integrating with LEDs or Displays:
- Use multiple LEDs to create a visual distance indicator.
- Integrate with a 7-segment or LCD display to show the distance numerically.
Creating a Proximity Alert System:

Set thresholds to trigger alerts (e.g., sound alarms when objects are too close).
Building a Simple Obstacle-Avoiding Robot:

Utilize the ultrasonic sensor to detect obstacles and navigate around them.

Conclusion

In this lesson, you’ve learned how to use an ultrasonic sensor module with the Raspberry Pi Pico to measure the distance to an object. By triggering ultrasonic pulses and measuring the echo time, you can accurately determine the distance of nearby objects. This project serves as a foundation for more complex applications in robotics, automation, and interactive systems.