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Getting started with ESP32 and MicroPython

Last update: 2020-03-31 11:00:00 -0300.

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Introduction

In this article I’m going to share my first experience playing with ESP32 microcontroller and MicroPython language. The main goal here is to setup the whole environment for development, sharing the steps taken to run my first program, because you know, sometimes even the most straight forward task can be very tricky to acomplish.

I’m a electrical engineer post graduated in automotive embedded systems and I’ve been working as software developer for 20 years, but never played with ESP32. I remember at the first time I’ve heard about ESP32, I was very busy with a new job, developing a computer vision embedded system that was Raspberry Pi based.

But last year I was mentoring some internals in my former company and they shown me some ESP32 based boards they were using in their projects, and I was very happy to see how fast they could prototype to build a proof of concept for these projects.

I mean, I love bare metal and build everything from scratch, but sometimes you just need to test an idea to see if it will work as expected, and I remember when I was in the college and my first contact with the Arduino platform.

And why Python? I heard about MicroPython in 2016 and probably I was looking for an oportunity to check this out. To be very honest, I don’t think that Python would be my first language of choice for an embedded project, surelly my options would be C, C++ and Lua, in that order, for many reasons that are out of the scope for this article. But let’s see how the things goes, may be I’ll be surprised.

Enough talking. To get started, it’s necessary to install all the tools to communicate with the board, upload the MicroPython firmware and run the first program to check if everything is working as expected.

There are two aspects that sometimes can be very annoying: since that there are a lot of manufacturers around, there are also a lot of ESP32 based boards around. Also, due to differences in some softwares versions, it’s very common to face some unexpected behaviour while trying to put everything up and running together. It worth to mention also the lack of proper documentation.

The devil is in the details and in fact, that’s why I wrote this article. The steps here are basically the same from the official documentations, always read the fucking manuals first (when available of course). My personal touch comes in the specific details, the approach and reasonable order for the steps and troubleshooting.

Here’s the hardware and software specifications for this article:

Set up the environment

Make sure that the current user is part of the dialout group:

$ id furansa | grep dialout

If is not, add it, then log out and in to make sure the changes will be propagated across the whole system:

$ sudo adduser furansa dialout

Plug the board in some of the USB ports and check if it will be recognized, and if the cp210x kernel module will be loaded. This also tells which port the board will be accessible:

$ sudo dmesg
usbserial: USB Serial support registered for generic
usbcore: registered new interface driver cp210x
usbserial: USB Serial support registered for cp210x
cp210x 1-7:1.0: cp210x converter detected
usb 1-7: cp210x converter now attached to ttyUSB0

It’s supposed to work out of the box for Ubuntu 20.04 and here, the board is accessible at /dev/ttyUSB0.

Some software are mandatory to be installed: esptool allows to flash the board and upload the MicroPython firmware and screen, the very famous terminal multiplexer and emulator.

$ sudo apt-get install esptool screen

Flash and upload the MicroPython firmware

Warning: this procedure can do permanent damage to the board, so, you’re at your own. That said, let’s continue >:-)

After download the MicroPython firmware for ESP32 boards from here (I’m using the generic v1.12-310-g9418611c8 as already mentioned), it’s possible to proceed by first erasing the current firmware:

$ esptool --chip esp32 --port /dev/ttyUSB0 erase_flash

esptool.py v2.8
Serial port /dev/ttyUSB0
Connecting........_____....._
Chip is ESP32D0WDQ6 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
Crystal is 40MHz
MAC: 24:62:ab:bb:d8:44
Enabling default SPI flash mode...
Erasing flash (this may take a while)...

A fatal error occurred: ESP32 ROM does not support function erase_flash.

Ouch! Barely started and the first critical error already showed up.

After look some posts at esptool GitHub and MicroPython forum, my best guess is that this error can be related with some incompatibility between the esptool and the current firmware. This is obvious by the error message, but I found few people reporting the same problem with older versions of esptool, and at the time of this writing I’m using the latest version (2.8). So, if you have a reasonable explanation for this error, I’ll appreciate if you contact me and let me know.

After try different options without luck, with different baud rates for example, I decided to ignore this error and proceed with the upload of the MicroPython firmware:

$ esptool --chip esp32 --port /dev/ttyUSB0 --baud 460800 write_flash -z 0x1000 esp32-idf3-20200327-v1.12-310-g9418611c8.bin

esptool.py v2.8
Serial port /dev/ttyUSB0
Connecting........_____....
Chip is ESP32D0WDQ6 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
Crystal is 40MHz
MAC: 24:62:ab:bb:d8:44
Changing baud rate to 460800
Changed.
Enabling default SPI flash mode...
Configuring flash size...
Auto-detected Flash size: 4MB
Erasing flash...
Compressed 1442640 bytes to 917380...
Took 3.83s to erase flash block
Wrote 1442640 bytes (917380 compressed) at 0x00001000 in 28.5 seconds (effective 405.3 kbit/s)...
Hash of data verified.

Leaving...
Hard resetting via RTS pin...

Hm, interesting! Looks like the upload was successfully completed and honestly I’m not sure if this is good, let’s see.

Connect to the board and access the REPL prompt

The REPL (Read Evaluate Print Loop) prompt is the interactive environment where you can type some commands and see its output, as the same way we do in a regular Python implementation. This is very convenient and one of the advantages of MicroPython, so, let’s connect using screen and try it out:

$ screen /dev/ttyUSB0 115200

FAT filesystem appears to be corrupted. If you had important data there, you
may want to make a flash snapshot to try to recover it. Otherwise, perform
factory reprogramming of MicroPython firmware (completely erase flash, followed
by firmware programming).

Oh, really man? I was not expecting a walk in the park but I was almost at the point of considering return back to the chicken farm. Again, I was not able to find out something more conclusive, but this post gave me some insight.

How I solved the problem: despite this error message, it was possible to access the REPL prompt after hitting the CTRL + C to stop the error printing.

FAT filesystem appears to be corrupted. If you had important data there, you
may want to make a flash snapshot to try to recover it. Otherwise, perform
factory reprogramming of MicroPython firmware (completely erase flash, followed
by firmware programming).

Traceback (most recent call last):
  File "_boot.py", line 11, in <module>
  File "inisetup.py", line 34, in setup
  File "inisetup.py", line 15, in check_bootsec
  File "inisetup.py", line 30, in fs_corrupted
KeyboardInterrupt: 
MicroPython v1.12-310-g9418611c8 on 2020-03-27; ESP32 module with ESP32
Type "help()" for more information.

And now we are able to format the board filesystem:

>>> import os
>>> os.VfsFat.mkfs(bdev)

So far so good (hope so), let’s test the system.

Test the system

Let’s play around and check if the system (hardware and software) is responding as expected. Still from the REPL, let’s blink the LED connected at GPIO pin 16.

Alternatively, it’s also possible to use the miniterm emulator that comes with PySerial module, after installed, the use is similar to screen:

$ sudo apt-get install python3-serial
$ python3 -m serial.tools.miniterm /dev/ttyUSB0 115200

And once connected:

>>> import machine
>>> pin16 = machine.Pin(16, machine.Pin.OUT)
>>> print(pin16.value())
0
>>> pin16.value(1)

Following the help message from the REPL terminal, it’s possible to connect to the wireless network:

>>> import network
>>> sta_if = network.WLAN(network.STA_IF); sta_if.active(True)
>>> sta_if.connect("NETWORK_NAME", "NETWORK_PASSWD")
>>> sta_if.isconnected()
True

Looks like everything is going well. And now for something completely different, or at least more interesting.

Upload files to the board

By uploading files to the board we’ll be able to do more interesting things. There are at least two tools to help with this, ampy and rshell.

When using Python’s pip to install packages, in general is not a good ideia to do this as root and install the packages system-wide. This can cause some incompatibilities in the future or even with already installed packages. The most indicated is to install as regular user or even better, to create a Python virtual environment for these.

Here I’m going to install both system-wide because it’s a dedicated system:

root@antares:~# pip3 install adafruit-ampy
...
Installing collected packages: python-dotenv, adafruit-ampy
Successfully installed adafruit-ampy-1.0.7 python-dotenv-0.12.0
root@antares:~# pip3 install rshell
...
Installing collected packages: pyudev, rshell
Successfully installed pyudev-0.22.0 rshell-0.0.27

Both ampy and rshell looks quite the same and at the very first moment, I’ve only missed a more detailed help documentation. Let’s perform some simple operations to put and list files inside the board.

This will allow us to think about a more structured organization for the future projects, for example, by separing the code blocks by functionality and/or responsability in Python modules inside different directories and files. That’s a good practice for any software architecture.

Initially, let’s create two simple files: boot.py that will hold the code that the system will execute after booting and main.py, as a main entry program.

The code is pretty straight forward, for the boot.py:

import esp

esp.osdebug(None)  # Disable debugging messages

And for the main.py:

from time import sleep
from machine import Pin

# Configure GPIO pin 16 as output
pin16 = Pin(16, Pin.OUT)

# Blink the board's LED at pin16 5 times
for i in range(5):
    pin16.value(1)
    sleep(0.5)
    pin16.value(0)
    sleep(0.5)

This is OK for a hardware Hello World! Now to upload these files with both ampy and/or rshell, notice that when using rshell the file is copied into the /pyboard directory inside the board:

$ ampy --port /dev/ttyUSB0 put boot.py
$ rshell --port /dev/ttyUSB0 cp main.py /pyboard/

To list the copied files:

$ ampy --port /dev/ttyUSB0 ls
$ rshell --port /dev/ttyUSB0 ls /pyboard

Now with the files already in place it’s possible to turn-off and turn-on the board and see the magic happening.

Play with the OLED display

Let’s finish with style by playing with the SSD1306 OLED display. Download the driver created by Adafruit from here and copy to the board:

$ rshell --port /dev/ttyUSB0 cp ssd1306.py /pyboard/

Modify and upload our main.py that now will import the driver and write to the display:

from time import sleep
from machine import I2C, Pin

import ssd1306

# Configure GPIO pin 16 as output
pin16 = Pin(16, Pin.OUT)

# Blink the board's LED at pin16 5 times
for i in range(5):
    pin16.value(1)
    sleep(0.5)
    pin16.value(0)
    sleep(0.5)

# I2C interface pins configuration
i2c = I2C(-1, scl=Pin(4), sda=Pin(5))

# Configure the display
oled_width = 128
oled_height = 64
oled = ssd1306.SSD1306_I2C(oled_width, oled_height, i2c)

# Setup the text and show the message
oled.text("Hello", 0, 0)
oled.text("MicroPython", 0, 10)
oled.text("at ESP32", 0, 20)
oled.show()

After restart the board you should be able to see the LED blinking five times and the message will be displayed.

Visual Studio Code as IDE

There are some extensions to work with MicroPython using Visual Studio Code and I choose the one recently released by Seeed.

This extension allow to connect to the board by clicking at the “Device Connection/Disconnection” icon in the status bar, and selecting the serial port.

After successfully connected, select the “Open MicroPython Terminal” icon at the status bar and voila, you’ll be in the REPL prompt.

Conclusion

In this article it was possible to walk through the first steps to set up and run MicroPython in the ESP32 board. Now it’s possible to use this environment to start to structure and develop a more complex embedded system project.

And that’s what I’m going to do in the next articles, by developing a monitoring system that will perform data acquisition, processing and visualization, also integrating with AWS.

References

Updated: 2020-08-31 13:02:25 +0000.