Hello MicroPython

Getting started

This howto assumes Ubuntu 18.04+ is used on the computer and several tools have been installed:

sudo apt install picocom make python3-pip
sudo pip3 install esptool adafruit-ampy

Clone the Git repository and run makefiles:

git clone https://git.k-space.ee/k-space/micropython-skeleton
cd micropython-skeleton
make

In order to access the serial port you likely need to add yourself to the dialout group after which you need to log out from your desktop session and log in again

sudo gpasswd -a $USER dialout

If you're using one of the computers prepared for the workshop all the steps above have been performed already for you

Usage

To open serial to the microcontroller:

make console

To upload main.py:

make upload

Note that serial connection is used by both so you can't upload scripts while serial console is open in another window

Blinking LED-s

First let's some LED-s blinking. Press Ctrl-E for paste mode, otherwise spaces get mangled. Press Ctrl-Shift-V for pasting. Press Ctrl-D to exit paste mode and evaluate the code.

from time import sleep
from machine import Pin

# RGB LED is connected to programmable pins 12, 13, 15
led_red = Pin(12, Pin.OUT)
led_green = Pin(13, Pin.OUT)
led_blue = Pin(15, Pin.OUT)

# The values are inverted because 3.3v is common pin
led_red.value(1)
led_green.value(1)
led_blue.value(1)

for j in range(0, 5):
    led_red.value(0)
    sleep(1)
    led_red.value(1)
    led_green.value(0)
    sleep(1)
    led_green.value(1)
    led_blue.value(0)
    sleep(1)
    led_blue.value(1)

Tasks:

1. Modify the code so yellow, cyan, magenda and white would be included.

Button presses

On the board there is button labelled "Boot", this is hooked up to pin 2. By default there is a resistor which pulls the voltage on the pin to 3.3v, but when button is pressed the pin is shorted to ground so the voltage goes to 0v. Most modern solutions use interrupts to detect voltage change on the pin:

from machine import Pin
from time import sleep

Pin(12, Pin.OUT).value(1)
Pin(13, Pin.OUT).value(1)
led_blue = Pin(15, Pin.OUT)
button = Pin(0)

turned_off = False

def callback(p):
    global turned_off
    turned_off = not turned_off
    led_blue.value(turned_off)

# Execute function 'callback' when voltage goes from 3.3v to 0v on pin 0
button.irq(trigger=Pin.IRQ_FALLING, handler=callback)

Tasks:

1. Modify the code so pressing button shuffles between off, red, green, blue, yellow, cyan, magenta and white

Driving OLED screens

Let's get some pixels on the screen! There's 128x64 pixels monochrome OLED screen connected via I2C bus on the pins 4 and 5.

from machine import Pin, SoftI2C
from ssd1306 import SSD1306_I2C

i2c = SoftI2C(Pin(4),Pin(5), freq=400000) # Bitbanged I2C bus
oled = SSD1306_I2C(128, 64, i2c)
oled.invert(0) # White text on black background
oled.contrast(255) # Maximum contrast

oled.fill(0)
name = "Hello MicroPython!"
oled.text("  %s" % name, 10, 10)
oled.show()

Tasks:

1. What IP address was assigned to the board by the wireless network? Hint: Check out wlan.ifconfig()
2. Show button press counter on the screen
3. Show on the screen which color is the RGB LED shining

Clock synchronization

Most boards to do not have battery backed time keep track of the time. Once you have the microcontroller connected to the Internet you can query time from one of the NTP servers.

The Internet connectivity is established using boot.py script that is already included in this repo. It by default connects to k-space.ee legacy wireless network.

Temperature & humidity

Next let's hook up DHT11 sensor to the board and measure the temperature.

• Sensor's Vcc is connected to 3.3v on the board
• Ground pins (GND) are connected
• Sensor's data pin is connected to board pin 4

Some code to get you going:

from time import sleep
from machine import Pin
from dht import DHT11

d = DHT11(Pin(4))

try:
    d.measure()
except OSError:
    print("Sensor not connected")
else:
    print("Temperature %sC" % d.temperature())
    print("Humidity %s%%" % d.humidity())
finally:
    sleep(1)

Tasks:

1. Get temperature and humidity displayed on the screen

Distance with sonar

In this case HC-SR04 is hooked up:

• Trigger is connected to pin 12
• Echo is connected to pin 14
• GND pins are connected
• Sonar's Vcc is connected to 3.3V on the board

This is exactly the case with the sumorobots. Feel free to try it out!

Code to measure distance:

from time import sleep_us, sleep_ms
from machine import Pin, time_pulse_us

trigger = Pin(12, Pin.OUT)
echo = Pin(14, Pin.IN)

def measure():
    trigger.value(0)
    sleep_us(5)
    trigger.value(1)
    sleep_us(10)
    trigger.value(0)

    duration = time_pulse_us(echo, 1, 29000)
    distance = (duration / 2.0) / 29
    return distance

while True:
    print("Distance is: %s cm" % measure())
    sleep_ms(200)

Tasks:

1. Get distance shown on OLED display
2. How were the constants for converting duration to distance figured out?

Summary

ESP32 microcontroller with MicroPython is a really cheap way to get started with the IoT stuff. See more detailed information here.

Other interesting projects with ESP8266 and ESP32 microcontrollers:

• Nixie clock with ESP8266
• Sumorobot with ESP32

Come and visit k-space.ee on Wednesdays 18:00 for more of MicroPython