It's easy to use the MCP3421 with Python or CircuitPython, and the Adafruit_CircuitPython_MCP3421 module. This module allows you to easily write Python code to read input on the ADC.
You can use this driver with any CircuitPython microcontroller board or with a computer that has GPIO and Python thanks to Adafruit_Blinka, our CircuitPython-for-Python compatibility library.
CircuitPython Microcontroller Wiring
First wire up the breakout to your board exactly as follows. The following is the breakout wired to a Feather RP2040 (shown using a STEMMA QT cable):
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Board STEMMA 3V to breakout VIN (red wire)
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Board STEMMA GND to breakout GND (black wire)
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Board STEMMA SCL to breakout SCL (yellow wire)
- Board STEMMA SDA to breakout SDA (blue wire)
The following is the breakout wired to a Feather RP2040 using a solderless breadboard:
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Board 3V to breakout VIN (red wire)
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Board GND to breakout GND (black wire)
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Board SCL to breakout SCL (yellow wire)
- Board SDA to breakout SDA (blue wire)
Python Computer Wiring
Since there are dozens of Linux computers/boards you can use, we will show wiring for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is supported.
Here's the Raspberry Pi wired with I2C using a STEMMA QT connector:
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Pi 3V to breakout VIN (red wire)
-
Pi GND to breakout GND (black wire)
-
Pi SCL to breakout SCL (yellow wire)
- Pi SDA to breakout SDA (blue wire)
Here's the Raspberry Pi wired with I2C using a solderless breadboard:
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Pi 3V to breakout VIN (red wire)
-
Pi GND to breakout GND (black wire)
-
Pi SCL to breakout SCL (yellow wire)
- Pi SDA to breakout SDA (blue wire)
Python Installation of MCP3421 Library
You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may also require enabling I2C on your platform and verifying you are running Python 3. Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready!
Once that's done, from your command line run the following command:
pip3 install adafruit-circuitpython-mcp3421
If your default Python is version 3 you may need to run 'pip' instead. Just make sure you aren't trying to use CircuitPython on Python 2.x, it isn't supported!
CircuitPython Usage
To use with CircuitPython, you need to first install the Adafruit_CircuitPython_MCP3421 library, and its dependencies, into the lib folder on your CIRCUITPY drive. Then you need to update code.py with the example script.
Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, and copy the entire lib folder and the code.py file to your CIRCUITPY drive.
Your CIRCUITPY/lib folder should contain the following folders:
- adafruit_bus_device/
- adafruit_mcp3421/
Python Usage
Once you have the library pip3 installed on your computer, copy or download the following example to your computer, and run the following, replacing code.py with whatever you named the file:
python3 code.py
Example Code
If running CircuitPython: Once everything is saved to the CIRCUITPY drive, connect to the serial console to see the data printed out!
If running Python: The console output will appear wherever you are running Python.
# SPDX-FileCopyrightText: Copyright (c) 2024 Liz Clark for Adafruit Industries
#
# SPDX-License-Identifier: MIT
import time
import board
import adafruit_mcp3421.mcp3421 as ADC
from adafruit_mcp3421.analog_in import AnalogIn
i2c = board.I2C()
adc = ADC.MCP3421(i2c, gain=1, resolution=14, continuous_mode=True)
adc_channel = AnalogIn(adc)
# gain, resolution and mode can also be set after instantiation:
# set gain to 1, 2, 4 or 8x
# defaults to 1
# adc.gain = 1
# set resolution to 12, 14, 16 or 18
# defaults to 14
# adc.resolution = 14
# set continuous read mode True or False for one-shot
# defaults to True
# adc.continuous_mode = True
while True:
print(f"ADC value: {adc_channel.value}")
print(f"Current gain: {adc.gain}X")
print(f"Current resolution: {adc.resolution}-bit")
if adc.continuous_mode:
mode = "continuous"
else:
mode = "one-shot"
print(f"Mode: {mode}")
print()
time.sleep(0.01)
The MCP3421 is initialized over I2C. Then in the loop, the analog input is read and printed to the serial monitor, along with the current gain, resolution and mode settings.
This ADC is great for reading sensors like strain gauges, pressure sensors, or thermocouples. It's not going to be great for reading stuff like potentiometers, where you have a single-end reading referenced to ground, and you want to read the full range from 0 to Vcc.
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