5.15. Exercise: HC-SR04

Instructions

1. Read the case study on Case Study: HC-SR04 Ultrasonic Sensor.

Question 1

Answer the following:

• Draw the pin states over time when a measurement is triggered.

You may wish to draw over the blank plots provided below.

Solution

Question 2

Answer the following:

• Create a wiring diagram of the sensor connected to your microcontroller using Wokwi.

Solution

Solution is locked

Question 3

Answer the following:

• Annotate the provided MicroPython code to match the steps outlined on the case study.

Note

The code provided is for the micro:Maqueen robot. You may need to adjust the pins used for your particular robot.

import utime

def ultrasound_measure():
    pin1.write_digital(1)
    utime.sleep_us(10)
    pin1.write_digital(0)

    timeout = utime.ticks_us()
    while True:
        pulseBegin = utime.ticks_us()
        if 1 == pin2.read_digital():
            break
        if (pulseBegin - timeout) > 5000:
            return -1  # error: no echo start detected

    while True:
        pulseEnd = utime.ticks_us()
        if 0 == pin2.read_digital():
            break
        if (pulseEnd - pulseBegin) > 5000:
            return -2  # error: echo too long (timeout)

    x = pulseEnd - pulseBegin   # time in µs
    d = x * 0.01715             # distance in cm
    return int(d)

while True:
    dist = ultrasound_measure()
    if dist >= 0: # only process valid readings
        print(dist)
        sleep(100)

Solution

Solution is locked

Question 4

The measurements from the HC-SR04 can be noisy.

Extend the code so that:

• the distance is smoothed using a moving average

• small changes are suppressed with deadband

Solution

Solution is locked