Home Code HC-SR04 Ultrasonic ranging module and Pyboard example in Micropython

HC-SR04 Ultrasonic ranging module and Pyboard example in Micropython

by shedboy71

In this example we connect a HC-SR04 Ultrasonic ranging module to a Pyboard

Ultrasonic ranging module HC – SR04 provides 2cm – 400cm non-contact measurement function, the ranging accuracy can reach to 3mm. The modules includes ultrasonic transmitters, receiver and control circuit.

The basic principle of work:

(1) Using IO trigger for at least 10us high level signal,
(2) The Module automatically sends eight 40 kHz and detect whether there is a pulse signal back.
(3) IF the signal back, through high level , time of high output IO duration is the time from sending ultrasonic to returning.
Test distance = (high level time×velocity of sound (340M/S) / 2

You only need to supply a short 10uS pulse to the trigger input to start the ranging, and then the module will send out an 8 cycle burst of ultrasound at 40 kHz and raise its echo. The Echo is a distance object that is pulse width and the range in proportion . You can calculate the range through the time interval between sending trigger signal and receiving echo signal.

Formula: uS / 58 = centimeters or uS / 148 =inch; or: the range = high level time * velocity (340M/S) / 2; we suggest to use over 60ms measurement cycle, in order to prevent trigger signal to the echo signal.


Parts List


Name Link
Pyboard Elecrow Core Board For MicroPython Crow Pyboard Development Board STM32F405RG for Pyboard
HC_SR04 Free shipping 1pcs Ultrasonic Module HC-SR04 Distance Measuring Transducer Sensor for Arduino
Connecting cables Free shipping Dupont line 120pcs 20cm male to male + male to female and female to female jumper wire



Wire connecting direct as following:

3v3 Supply
Trigger Pulse Input
Echo Pulse Output
0V Ground


pyboard and hc-sr04

pyboard and hc-sr04


2 parts to this an ultrasonic library

[codesyntax lang=”python”]

# Ultrasonic library for MicroPython's pyboard.
# Compatible with HC-SR04 and SRF04.
# Copyright 2014 - Sergio Conde Gómez <skgsergio@gmail.com>
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import pyb

# Pin configuration.
# WARNING: Do not use PA4-X5 or PA5-X6 as the echo pin without a 1k resistor.

class Ultrasonic:
    def __init__(self, tPin, ePin):
        self.triggerPin = tPin
        self.echoPin = ePin

        # Init trigger pin (out)
        self.trigger = pyb.Pin(self.triggerPin)
        self.trigger.init(pyb.Pin.OUT_PP, pyb.Pin.PULL_NONE)

        # Init echo pin (in)
        self.echo = pyb.Pin(self.echoPin)
        self.echo.init(pyb.Pin.IN, pyb.Pin.PULL_NONE)

    def distance_in_inches(self):
        return (self.distance_in_cm() * 0.3937)

    def distance_in_cm(self):
        start = 0
        end = 0

        # Create a microseconds counter.
        micros = pyb.Timer(2, prescaler=83, period=0x3fffffff)

        # Send a 10us pulse.

        # Wait 'till whe pulse starts.
        while self.echo.value() == 0:
            start = micros.counter()

        # Wait 'till the pulse is gone.
        while self.echo.value() == 1:
            end = micros.counter()

        # Deinit the microseconds counter

        # Calc the duration of the recieved pulse, divide the result by
        # 2 (round-trip) and divide it by 29 (the speed of sound is
        # 340 m/s and that is 29 us/cm).
        dist_in_cm = ((end - start) / 2) / 29

        return dist_in_cm


Now you copy that file to your Pyboard and then modify main.py as follows

[codesyntax lang=”python”]

import pyb
import ultrasonic

# setting pins to accomodate Ultrasonic Sensor (HC-SR04)
sensor1_trigPin = pyb.Pin.board.X1
sensor1_echoPin = pyb.Pin.board.X2

# sensor needs 5V and ground to be connected to pyboard's ground
# creating two Ultrasonic Objects using the above pin config
sensor1 = ultrasonic.Ultrasonic(sensor1_trigPin, sensor1_echoPin)

# using USR switch to print the sensor's values when pressed
switch = pyb.Switch()

# function that prints each sensor's distance
def print_sensor_values():
	# get sensor1's distance in cm
	distance1 = sensor1.distance_in_cm()
	print("Sensor1 (Metric System)", distance1, "cm")

# prints values every second
while True:



Open up the REPL window. Here is what I saw

Sensor1 (Metric System) 0.3965517 cm
Sensor1 (Metric System) 0.3793103 cm

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