MicroPython ESP32 Tutorial - Interfacing Ultrasonic Sensor

October 22, 2020

MicroPython-ESP32-Tutorial-Interfacing-Ultrasonic-Sensor-1
In this MicroPython ESP32 Tutorial, we will be interfacing Ultrasonic Sensor HC-SR04 with MakePython ESP32 using MicroPython Code.

1. Overview: MicroPython on ESP32 with Ultrasonic Sensor

In this project, we will be interfacing the HC-SR04 Ultrasonic Sensor with ESP32 using MicroPython Code. We will use Ultrasonic Sensor with ESP32 Board & 0.96″ I2C OLED Display. We will then write a MicroPython Code in uPyCraft IDE. Using the uPyCraft IDE, we can directly upload the firmware to ESP32 Board.
 
HC-SR04 is an ultrasonic sensor mainly used to determine the distance of the target object. It measures accurate distance using a non-contact technology – A technology that involves no physical contact between sensor and object.
 
Before proceeding, you can check this Guide: MicroPython ESP32 Tutorial - Getting Started. I highly recommend you follow this guide as it covers all the basics including setting up the IDE to writing the code & uploading as well.

2. MakePython ESP32 Dev Board

The board contains a combined ESP32 Chip + 1.3″ I2C OLED Display that supports MicroPython. To learn more about this board and purchase it online, you can visit this link: MakePython ESP32 Board. This MakePython ESP32 dev board is cheaper with an additional 1.3″ OLED display and is specially designed for MicroPython support. With 2 versions to choose from, WROOM(No PSRAM) and WROVER((8MB PSRAM).
MakePython-ESP32-WROVER

3. HC-SR04 Ultrasonic Sensor

The HC-SR04 is an ultrasonic distance sensor. This economical sensor provides 2cm to 400cm of non-contact measurement functionality with a ranging accuracy that can reach up to 3mm. The HC-SR04 module contains an ultrasonic transmitter, a receiver, and a control circuit.
HC-SR04-Ultrasonic-Sensor
There are only four pins on the HC-SR04: VCC (Power), Trig (Trigger), Echo (Receive), and GND (Ground). This sensor has additional control circuitry that can prevent inconsistent “bouncy” data depending on the application.
 
To learn more about this sensor and learn its basic application, you can visit this link: Distance Measurement with Ultrasonic Sensor.

4. Interfacing Ultrasonic Sensor HC-SR04 with ESP32 using MicroPython

Here is a circuit diagram for Interfacing Ultrasonic Sensor HC-SR04 with ESP32 using MicroPython Code. The TRIG pin is connected to ESP32 GPIO13 Pin & the ECHO pin is connected to ESP32 GPIO12 Pin. Similarly, the VCC is connected to 5V & GND is connected to GND.
 
Circuit-Diagram-for-Interfacing-HC-SR04-with-ESP32
In case if you are using MakePython ESP32 Board, you can do the following connection as shown in the connection diagram below.
Circuit-Diagram-MakePython-ESP32-HC-SR04

5. Source Code/ Program

The MicroPython Code for using Ultrasonic Sensor with ESP32 has three parts. This is because we need a library for HC-SR04 Ultrasonic Sensor and OLED Display.
The three parts include:
1. SSD1306.py
2. HC_SR04.py
3. Main.py

5.1 SSD1306.py

The library to write to the OLED display isn’t part of the standard MicroPython library by default. So, first, we need to upload the library to the ESP32 board.
 
# MicroPython SSD1306 OLED driver, I2C and SPI interfaces
from micropython import const
import time
import framebuf
import sys

currentBoard=""
if(sys.platform=="esp8266"):
  currentBoard="esp8266"
elif(sys.platform=="esp32"):
  currentBoard="esp32"
elif(sys.platform=="pyboard"):
  currentBoard="pyboard"
  import pyb
# register definitions
SET_CONTRAST        = const(0x81)
SET_ENTIRE_ON       = const(0xa4)
SET_NORM_INV        = const(0xa6)
SET_DISP            = const(0xae)
SET_MEM_ADDR        = const(0x20)
SET_COL_ADDR        = const(0x21)
SET_PAGE_ADDR       = const(0x22)
SET_DISP_START_LINE = const(0x40)
SET_SEG_REMAP       = const(0xa0)
SET_MUX_RATIO       = const(0xa8)
SET_COM_OUT_DIR     = const(0xc0)
SET_DISP_OFFSET     = const(0xd3)
SET_COM_PIN_CFG     = const(0xda)
SET_DISP_CLK_DIV    = const(0xd5)
SET_PRECHARGE       = const(0xd9)
SET_VCOM_DESEL      = const(0xdb)
SET_CHARGE_PUMP     = const(0x8d)
class SSD1306:
  def __init__(self, width, height, external_vcc):
    self.width = width
    self.height = height
    self.external_vcc = external_vcc
    self.pages = self.height // 8
    self.buffer = bytearray(self.pages * self.width)
    self.framebuf = framebuf.FrameBuffer(self.buffer, self.width, self.height, framebuf.MVLSB)
    self.poweron()
    self.init_display()
  def init_display(self):
    for cmd in (
      SET_DISP | 0x00, # off
      # address setting
      SET_MEM_ADDR, 0x00, # horizontal
      # resolution and layout
      SET_DISP_START_LINE | 0x00,
      SET_SEG_REMAP | 0x01, # column addr 127 mapped to SEG0
      SET_MUX_RATIO, self.height - 1,
      SET_COM_OUT_DIR | 0x08, # scan from COM[N] to COM0
      SET_DISP_OFFSET, 0x00,
      SET_COM_PIN_CFG, 0x02 if self.height == 32 else 0x12,
      # timing and driving scheme
      SET_DISP_CLK_DIV, 0x80,
      SET_PRECHARGE, 0x22 if self.external_vcc else 0xf1,
      SET_VCOM_DESEL, 0x30, # 0.83*Vcc
      # display
      SET_CONTRAST, 0xff, # maximum
      SET_ENTIRE_ON, # output follows RAM contents
      SET_NORM_INV, # not inverted
      # charge pump
      SET_CHARGE_PUMP, 0x10 if self.external_vcc else 0x14,
      SET_DISP | 0x01): # on
      self.write_cmd(cmd)
    self.fill(0)
    self.show()
  def poweroff(self):
    self.write_cmd(SET_DISP | 0x00)
  def contrast(self, contrast):
    self.write_cmd(SET_CONTRAST)
    self.write_cmd(contrast)
  def invert(self, invert):
    self.write_cmd(SET_NORM_INV | (invert & 1))
  def show(self):
    x0 = 0
    x1 = self.width - 1
    if self.width == 64:
      # displays with width of 64 pixels are shifted by 32
      x0 += 32
      x1 += 32
    self.write_cmd(SET_COL_ADDR)
    self.write_cmd(x0)
    self.write_cmd(x1)
    self.write_cmd(SET_PAGE_ADDR)
    self.write_cmd(0)
    self.write_cmd(self.pages - 1)
    self.write_data(self.buffer)
  def fill(self, col):
    self.framebuf.fill(col)
  def pixel(self, x, y, col):
    self.framebuf.pixel(x, y, col)
  def scroll(self, dx, dy):
    self.framebuf.scroll(dx, dy)
  def text(self, string, x, y, col=1):
    self.framebuf.text(string, x, y, col)
  def hline(self, x, y, w, col):
    self.framebuf.hline(x, y, w, col)
  def vline(self, x, y, h, col):
    self.framebuf.vline(x, y, h, col)
  def line(self, x1, y1, x2, y2, col):
    self.framebuf.line(x1, y1, x2, y2, col)
  def rect(self, x, y, w, h, col):
    self.framebuf.rect(x, y, w, h, col)
  def fill_rect(self, x, y, w, h, col):
    self.framebuf.fill_rect(x, y, w, h, col)
  def blit(self, fbuf, x, y):
    self.framebuf.blit(fbuf, x, y)

class SSD1306_I2C(SSD1306):
  def __init__(self, width, height, i2c, addr=0x3c, external_vcc=False):
    self.i2c = i2c
    self.addr = addr
    self.temp = bytearray(2)
    super().__init__(width, height, external_vcc)
  def write_cmd(self, cmd):
    self.temp[0] = 0x80 # Co=1, D/C#=0
    self.temp[1] = cmd
    #IF SYS  :
    global currentBoard
    if currentBoard=="esp8266" or currentBoard=="esp32":
      self.i2c.writeto(self.addr, self.temp)
    elif currentBoard=="pyboard":
      self.i2c.send(self.temp,self.addr)
    #ELSE:

  def write_data(self, buf):
    self.temp[0] = self.addr << 1
    self.temp[1] = 0x40 # Co=0, D/C#=1
    global currentBoard
    if currentBoard=="esp8266" or currentBoard=="esp32":
      self.i2c.start()
      self.i2c.write(self.temp)
      self.i2c.write(buf)
      self.i2c.stop()
    elif currentBoard=="pyboard":
      #self.i2c.send(self.temp,self.addr)
      #self.i2c.send(buf,self.addr)
      self.i2c.mem_write(buf,self.addr,0x40)
  def poweron(self):
    pass

class SSD1306_SPI(SSD1306):
  def __init__(self, width, height, spi, dc, res, cs, external_vcc=False):
    self.rate = 10 * 1024 * 1024
    dc.init(dc.OUT, value=0)
    res.init(res.OUT, value=0)
    cs.init(cs.OUT, value=1)
    self.spi = spi
    self.dc = dc
    self.res = res
    self.cs = cs
    super().__init__(width, height, external_vcc)
  def write_cmd(self, cmd):
    global currentBoard
    if currentBoard=="esp8266" or currentBoard=="esp32":
      self.spi.init(baudrate=self.rate, polarity=0, phase=0)
    elif currentBoard=="pyboard":
      self.spi.init(mode = pyb.SPI.MASTER,baudrate=self.rate, polarity=0, phase=0)
    self.cs.high()
    self.dc.low()
    self.cs.low()
    global currentBoard
    if currentBoard=="esp8266" or currentBoard=="esp32":
      self.spi.write(bytearray([cmd]))
    elif currentBoard=="pyboard":
      self.spi.send(bytearray([cmd]))
    self.cs.high()
  def write_data(self, buf):
    global currentBoard
    if currentBoard=="esp8266" or currentBoard=="esp32":
      self.spi.init(baudrate=self.rate, polarity=0, phase=0)
    elif currentBoard=="pyboard":
      self.spi.init(mode = pyb.SPI.MASTER,baudrate=self.rate, polarity=0, phase=0)
    self.cs.high()
    self.dc.high()
    self.cs.low()
    global currentBoard
    if currentBoard=="esp8266" or currentBoard=="esp32":
      self.spi.write(buf)
    elif currentBoard=="pyboard":
      self.spi.send(buf)
    self.cs.high()
  def poweron(self):
    self.res.high()
    time.sleep_ms(1)
    self.res.low()
    time.sleep_ms(10)
    self.res.high()
First, open a new file in uPyCraft IDE paste the above code. Save the file as a name “SSD1306.py“. Click the “Download & Run” Icon. This will upload the file to the ESP32 board.
 
The uPyCraft console window should the following message.
uPyCraft-Console-Window

Now you can import the SSD1306 Library and use it on the Code Part.

5.2 HC_SR04.py

Now open a new tab and upload the following code. The code will upload the Ultrasonic Sensor HC_SR04 Library to ESP32 Board.
 
import machine, time
from machine import Pin

class HCSR04:
    """
    Driver to use the untrasonic sensor HC-SR04.
    The sensor range is between 2cm and 4m.
    The timeouts received listening to echo pin are converted to OSError('Out of range')
    """
    # echo_timeout_us is based in chip range limit (400cm)
    def __init__(self, trigger_pin, echo_pin, echo_timeout_us=500*2*30):
        """
        trigger_pin: Output pin to send pulses
        echo_pin: Readonly pin to measure the distance. The pin should be protected with 1k resistor
        echo_timeout_us: Timeout in microseconds to listen to echo pin.
        By default is based in sensor limit range (4m)
        """
        self.echo_timeout_us = echo_timeout_us
        # Init trigger pin (out)
        self.trigger = Pin(trigger_pin, mode=Pin.OUT, pull=None)
        self.trigger.value(0)

        # Init echo pin (in)
        self.echo = Pin(echo_pin, mode=Pin.IN, pull=None)

    def _send_pulse_and_wait(self):
        """
        Send the pulse to trigger and listen on echo pin.
        We use the method `machine.time_pulse_us()` to get the microseconds until the echo is received.
        """
        self.trigger.value(0) # Stabilize the sensor
        time.sleep_us(5)
        self.trigger.value(1)
        # Send a 10us pulse.
        time.sleep_us(10)
        self.trigger.value(0)
        try:
            pulse_time = machine.time_pulse_us(self.echo, 1, self.echo_timeout_us)
            return pulse_time
        except OSError as ex:
            if ex.args[0] == 110: # 110 = ETIMEDOUT
                raise OSError('Out of range')
            raise ex

    def distance_mm(self):
        """
        Get the distance in milimeters without floating point operations.
        """
        pulse_time = self._send_pulse_and_wait()

        # To calculate the distance we get the pulse_time and divide it by 2
        # (the pulse walk the distance twice) and by 29.1 becasue
        # the sound speed on air (343.2 m/s), that It's equivalent to
        # 0.34320 mm/us that is 1mm each 2.91us
        # pulse_time // 2 // 2.91 -> pulse_time // 5.82 -> pulse_time * 100 // 582
        mm = pulse_time * 100 // 582
        return mm

    def distance_cm(self):
        """
        Get the distance in centimeters with floating point operations.
        It returns a float
        """
        pulse_time = self._send_pulse_and_wait()

        # To calculate the distance we get the pulse_time and divide it by 2
        # (the pulse walk the distance twice) and by 29.1 becasue
        # the sound speed on air (343.2 m/s), that It's equivalent to
        # 0.034320 cm/us that is 1cm each 29.1us
        cms = (pulse_time / 2) / 29.1
        return cms

5.3 Main.py

After downloading the SSD1306.py & HC_SR04.py file to the ESP32 Board, you can now upload the main code. To do that open another file and paste the below code. Save it as a name “main.py“.
 
from hcsr04 import HCSR04
from machine import Pin,I2C
import ssd1306
 
i2c = I2C(scl=Pin(5), sda=Pin(4), freq=100000)      #Init i2c
lcd=ssd1306.SSD1306_I2C(128,64,i2c)
 
sensor = HCSR04(trigger_pin=13, echo_pin=12,echo_timeout_us=1000000)
 
try:
  while True:
    distance = sensor.distance_cm()
    print(distance)
    lcd.fill(0)
    lcd.text("Distance:",30,20)
    lcd.text(str(distance),30,40)
    lcd.show()
except KeyboardInterrupt:
       pass    

6. Testing the Ultrasonic Range Finder

Once the MicroPython code is uploaded to ESP32 Board, the Ultrasonic Sensor will start showing the distance in cm. You can check the working of the sensor by placing something in front of the sensor.
MicroPython-ESP32-with-Ultrasonic-Sensor

Ultrasonic range finders are fun little sensors that can measure distance. You can use them to find the distance to an object or to detect when something is near the sensor like a motion detector. Because they use sound to measure distance, they work just as well in the dark as they do in the light. It can measure distances from 2 cm up to 400 cm with an accuracy of ±3 mm.

This article is originally posted on How2electronics. If you have any further questions, or need some PCBA customizations based on those MakePython IoT boards, feel free to contact service@makerfabs.com.wink

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