Adafruit Industries MCP2221 User Manual

CircuitPython Libraries on any Computer with MCP2221

Created by Carter Nelson

Last updated on 2021-04-26 06:05:02 PM EDT

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Guide Contents

Guide Contents Overview

CircuitPython and CircuitPython Libraries CircuitPython Libraries on Personal Computers

Setup

Additional Information

Windows Have Python 3 Installed Install hidapi

Install Blinka

Set Environment Variable Check Platform was detected Mac OSX Python 3 Check Install hidapi Install Blinka Set Environment Variable Check that Platform was detected Linux

Install libusb and libudev Setup udev rules Install hidapi Remove Native MCP2221 Driver Install Blinka Set environment variable Run the sanity check.

Post Install Checks

Check that hidapi is installed correctly Check that MCP2221 can be found Check environment variable within Python

Pinout

Power Pins GPIO Pins I2C Pins UART Pins ADC Pins DAC Pins

Logic Level Examples

Installing Libraries for Breakouts

GPIO

Digital Output Digital Input Digtal Input and Output

I2C

Install MSA301 Library Example Code

ADC

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DAC UART

Install pySerial Find COM port in Linux Find COM port in Windows UART Example with GPS

FAQ & Troubleshooting

Update Blinka/Platform Libraries Getting an error message about "board" not found or "board" has no attribute Mixed SPI mode devices Why am I getting AttributeError: 'SpiDev' object has no attribute 'writebytes2'? No Pullup/Pulldown support on some linux boards or MCP2221 Getting OSError: read error with MCP2221 Using FT232H with other FTDI devices. I can't get neopixel, analogio, audioio, rotaryio, displayio or pulseio to work! Help, I'm getting the message "error while loading shared libraries: libgpiod.so.2: cannot open shared object file: No such file or directory" When running the libgpiod script, I see the message: configure: error: "libgpiod needs linux headers version >= v5.5.0"

Downloads Schematic and Fab Print

Overview

This guide will show you how to use an MCP2221(A) to connect to I2C sensors and breakouts from your desktop PC running Windows, Mac OSX, or Linux. The MCP2221 also allows for general purpose digital input and output (GPIO) for things like buttons and LEDs, analog to digital conversion (ADC), and digital to analog (DAC).

The cool part about this is that you can then use any of the CircuitPython Libraries that have been written for the numerous I2C sensors and breakouts. You can bring that data directly into your PC for any kind of powerful analysis or presentation.

 Our breakout uses the MCP2221A chip, but we may refer to it as MCP2221 as the difference are not relevant to using Blinka/CircuitPython libraries and use can use either version of the chip!

CircuitPython and CircuitPython Libraries

As you are going through this guide, keep in mind the difference between CircuitPython and CircuitPython Libraries:

CircuitPython - a microprocessor specific implementation of Python written in C. Here's the source

code (https://adafru.it/tB7). And here's the main CircuitPython guide (https://adafru.it/cpy-welcome).

CircuitPython Libraries - sensor and breakout specific code written in Python using the CircuitPython hardware API. There are a lot of these - check out the bundle (https://adafru.it/zdx).

There are various hardware combinations that allow for running CircuitPython and CircuitPython Libraries. In this guide we will not be using the actual CircuitPython firmware. But we will be using CircuitPython Libraries.

CircuitPython Libraries on Personal Computers

This is essentially the same idea as discussed in the FT232H Guide (https://adafru.it/GNe). How can we directly connect common hardware items like buttons and I2C breakouts to a PC?

The MCP2221 provides another way to do this by utlizing the USB bus. The MCP2221 just makes different trade offs relative to the FT232H. The biggest being no hardware SPI support . But you do gain ADC and DAC support. Also, it's much cheaper than the FT232H.

So you end up with something like this:

Great! Let's get everything setup so we can actually do some fun stuff.

Your browser does not support the video tag. Adafruit MCP2221A Breakout - General Purpose USB to GPIO ADC I2C

Wouldn't it be cool to drive a tiny OLED display, read a Out of Stock

Out of

Stock

Setup

The support for the MCP2221 in Blinka utilizes the hidapi library (https://adafru.it/HEI). This in turn relies on a few other things which vary for different OS's. So before we can actually use the MCP2221, we need to get everything setup. See the OS specific sections for what we went through to get things working for each.

Additional Information

Just for reference, here's the README from the hidapi source code repo, which has some install information:

https://adafru.it/HEJ

But first try the install instructions on the pages that follow for your OS.

https://adafru.it/HEJ

Windows Have Python 3 Installed

We assume you already have Python 3 installed on your computer. Note we do not support Python 2 - it's deprecated and no longer supported!

At your command line prompt of choice, check your Python version with python --version

Install hidapi

From the command line, manually install hidapi with

pip3 install hidapi

If the install fails with text that ends with something like:

distutils.errors.DistutilsError: Setup script exited with error: Microsoft Visual C++ 14.0 is required. Get it with "Microsoft Visual C++ Build Tools":

https://visualstudio.microsoft.com/downloads/ (https://adafru.it/JBp)

then you will need to also install the Microsoft Visual C++ Build Tools. Thanks to @jklem for pointing this out in the forums (https://adafru.it/doW).

Download it from here (same link as in text):

https://adafru.it/JBp

NOTE: You do not need the full Visual Studio IDE. Just the Build Tools.

https://adafru.it/JBp

Scroll down to where it says Tools for Visual Studio

2019.

Expand the list to show the sub options. Click the Download button for Build Tools for Visual Studio 2019.

This downloads a .exe file with a name like vs_BuildTools.exe. Run that to install the build tools and then try the pip install again.

Install Blinka

To install Blinka and its dependencies, run:

pip3 install adafruit-blinka

Set Environment Variable

You must do this every time before running circuitpython code, you can set it permanently in windows if you like, for now just type into the same cmd window you're using with Python

set BLINKA_MCP2221=1

If you are using Windows Powershell, the syntax is a little different. In that case do:

$env:BLINKA_MCP2221=1

Check Platform was detected

In the same command window you set BLINKA_MCP2221=1 env var, run python and run

import board

dir(board)

at the Python REPL. If you get no errors, and you see a list of all the pins available - you're good to go!

Mac OSX Python 3 Check

We assume you already have Python 3 installed on your computer. Note we do not support Python 2 - it's deprecated and no longer supported!

At your command line prompt of choice, check your Python version with python3 --version

Install hidapi

From the command line, manually install hidapi (https://adafru.it/HIA) with:

pip3 install hidapi

Install Blinka

To install Blinka (https://adafru.it/BJX) and its dependencies, run:

pip3 install adafruit-blinka

Set Environment Variable

You'll need to set this variable every time before running CircuitPython code. To do this, we set the environment variable to BLINKA_MCP2221.,

You can set the variable by running:

export BLINKA_MCP2221="1"

Then, verify that the variable is set by running:

echo $BLINKA_MCP2221

 Don't forget this step. Things won't work unless BLINKA_MCP2221 is set.

Check that Platform was detected

In the same terminal window you ran export BLINKA_MCP2221="1" , run python3 .

At the REPL, run:

import board

dir(board)

If you get no errors and see a list of all the pins available, you're good to go!

Linux

The following shows a typical run through installing and setting things up on Linux.

Install libusb and libudev

Run the following:

sudo apt-get install libusb-1.0 libudev-dev

and answer Y to the prompt. This should install libusb and libudev.

Setup udev rules

Use a text editor to create and edit the file /etc/udev/rules.d/99-mcp2221.rules and add the following contents.

SUBSYSTEM=="usb", ATTRS{idVendor}=="04d8", ATTR{idProduct}=="00dd", MODE="0666"

Here we use nano, so run:

like this:

and add the contents from above:

and then press CTRL-X and Y to save and exit.

Adafruit Industries MCP2221 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual