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2.13 Ultrasonic Sensor Module

Introduction

The ultrasonic sensor module uses ultrasonic waves to measure distances with remarkable accuracy. It emits ultrasonic waves and listens for their echo, calculating the distance based on the time taken for the echo to return. This versatile technology is commonly used in robotics, obstacle detection, and range-finding applications.

What You’ll Need

Here are the components required for this project:

COMPONENT INTRODUCTION	PURCHASE LINK
Jumper Wires	BUY
Ultrasonic Module	BUY
Fusion HAT+	-
Raspberry Pi	-

Circuit Diagram

Below is the schematic diagram for the ultrasonic sensor module:

Wiring Diagram

Assemble the circuit as shown in the diagram below:

Ensure the connections are secure, with the Echo pin connected to GPIO 22 and the Trigger pin to GPIO 27 of the Raspberry Pi.

Running the Example

All example code used in this tutorial is available in the ai-lab-kit directory. Follow these steps to run the example:

cd ~/ai-lab-kit/python/
sudo python3 2.13_Ultrasonic.py

This Python script uses an ultrasonic distance sensor to measure the distance to an object and displays the result on the console. When executed:

The sensor, connected to GPIO pins 27 (trigger) and 22 (echo), continuously measures the distance to the nearest object.
The distance is calculated in meters and converted to centimeters, then displayed in the format: Distance: <value> cm with two decimal places of precision.
The distance is updated every 0.3 seconds, allowing for near real-time monitoring.
The program runs indefinitely until interrupted with Ctrl+C, at which point it exits gracefully.

Code

Below is the Python code for this project:

# Import Ultrasonic and Pin class
from fusion_hat.modules import Ultrasonic
from fusion_hat.pin import Pin
from time import sleep

# Create Ultrasonic object
sensor = Ultrasonic(Pin(27), Pin(22))

try:
   # Main loop to continuously measure and report distance
   while True:
      dis = sensor.read() # Measure distance in centimeters
      print('Distance: {:.2f} cm'.format(dis))  # Print the distance with two decimal precision
      sleep(0.3)  # Wait for 0.3 seconds before the next measurement

except KeyboardInterrupt:
   # Handle KeyboardInterrupt (Ctrl+C) to gracefully exit the loop
   pass

Understanding the Code

Imports:
```
from fusion_hat.modules import Ultrasonic
from fusion_hat.pin import Pin
from time import sleep
```
The script imports the Ultrasonic class from the fusion_hat library to interact with the ultrasonic sensor and the sleep function from the time module to introduce delays.
Initialization:
```
sensor = Ultrasonic(Pin(27), Pin(22))
```
The ultrasonic sensor is initialized with the Echo pin connected to GPIO 22 and the Trigger pin to GPIO 27. This setup enables the Raspberry Pi to send and receive ultrasonic signals.
Main Loop:
```
while True:
   dis = sensor.read() # Measure distance in centimeters
   print('Distance: {:.2f} cm'.format(dis))  # Print the distance with two decimal precision
   sleep(0.3)  # Wait for 0.3 seconds before the next measurement
```
- Continuously measures the distance to the nearest object.
- Converts the distance from meters to centimeters.
- Prints the distance with two decimal places of precision.
- Includes a 0.3-second delay to allow the sensor to stabilize between measurements.
Graceful Exit:

The try-except block ensures the program exits cleanly when interrupted with Ctrl+C.
```
except KeyboardInterrupt:
   pass
```

Troubleshooting

No Distance Output:
- Cause: The sensor is not properly connected or powered.
- Solution:
  - Ensure the trigger pin is connected to GPIO 27 and the echo pin to GPIO 22.
  - Verify that the sensor has a stable power supply.
Constant or Incorrect Distance Values:
- Cause: Obstacles are too close or too far from the sensor, or there is interference.
- Solution:
  - Ensure the object is within the sensor’s effective range (typically 2 cm to 400 cm).
  - Check for interference from other ultrasonic devices or reflective surfaces.
Distance Always Zero:
- Cause: Faulty sensor or incorrect wiring.
- Solution: Test the sensor on another GPIO setup or replace it if faulty. Double-check the wiring configuration.

Extendable Ideas

Threshold-Based Alerts: Trigger an alert when the measured distance is below a specific threshold:

if dis < 10:
    print("Warning: Object too close!")

Auditory Feedback: Add a buzzer that sounds when the distance is below a threshold:

from fusion_hat import Buzzer
buzzer = Buzzer(Pin(4))
if dis < 10:
   buzzer.on()
else:
   buzzer.off()

Conclusion

This project demonstrates how to use an ultrasonic sensor module to measure distances with a Raspberry Pi. By understanding the principles of ultrasonic wave detection and GPIO programming, you can integrate such sensors into a variety of applications, from robotics to home automation. With this foundation, you can explore more advanced projects involving sensors and real-world interaction.