It's easy to use the PCF8591 with Python or CircuitPython, and the Adafruit CircuitPython PCF8591 module. This library allows you to easily write Python code that reads ADC values and set DAC voltages

You can use this sensor 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

Wire up a PCF8591 to your board exactly as shown below. Here's an example of wiring a Feather M4 to the sensor with I2C using a solderless breadboard

  • Board 3V to PCF8591 VIN (red wire)
  • Board GND to PCF8591 GND (black wire)
  • Board SCL to PCF8591 SCL (yellow wire)
  • Board SDA to PCF8591 SDA (blue wire)
  • PCF8591 A0 to PCF8591 Out

Python Computer Wiring

Since there's 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 to the sensor using I2C and a solderless breadboard

  • Board 3V to PCF8591 VIN (red wire)
  • Board GND to PCF8591 GND (black wire)
  • Board SCL to PCF8591 SCL (yellow wire)
  • Board SDA to PCF8591 SDA (blue wire)
  • PCF8591 A0 to PCF8591 Out

CircuitPython Installation of PCF8591 Library

You'll need to install the Adafruit CircuitPython PCF8591 library on your CircuitPython board.

First make sure you are running the latest version of Adafruit CircuitPython for your board.

Next you'll need to install the necessary libraries to use the hardware--carefully follow the steps to find and install these libraries from Adafruit's CircuitPython library bundle

Our CircuitPython starter guide has a great page on how to install the library bundle.

Before continuing make sure your board's lib folder or root filesystem has the adafruit_PCF8591.mpy file and adafruit_bus_device folder copied over.

Next connect to the board's serial REPL so you are at the CircuitPython >>> prompt.

Python Installation of PCF8591 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:

sudo pip3 install adafruit-circuitpython-pcf8591

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 & Python Usage

To demonstrate the usage of the ADC and DAC we'll initialize it and set the DAC and read the ADC  from the board's Python REPL.

Run the following code to import the necessary modules and initialize the I2C connection with the sensor:

import time
import board

import adafruit_pcf8591.pcf8591 as PCF
from adafruit_pcf8591.analog_in import AnalogIn
from adafruit_pcf8591.analog_out import AnalogOut

i2c = board.I2C()
pcf = PCF.PCF8591(i2c)
The Adafruit_CircuitPython_PCF8591 library assumes a 3.3V logic level and reference voltage. See the library documentation for details on how to specify a different reference voltage

Next we will create an AnalogIn and AnalogOutfrom the PCF8591 to allow us to set and read voltages the same way as with other CircuitPython boards with built in DACs and ADCs

pcf_in_0 = AnalogIn(pcf, PCF.A0)
pcf_out = AnalogOut(pcf, PCF.OUT)

Now that we are all set up, we will use the code below to set the DAC's value and then read the voltage that was set using the ADC. A little math will translate the raw 16-bit (scaled from 8-bit) value to a voltage level.

pcf_out.value = 65535
raw_value = pcf_in_0.value
scaled_value = (raw_value / 65535) * pcf_in_0.reference_voltage
print("Pin 0: %0.2fV" % (scaled_value))
print("")

Next we'll repeat the process but this time we'll specify a DAC value that was half the previous amount. Note how the voltage level changes as a result

pcf_out.value = 32767
raw_value = pcf_in_0.value
scaled_value = (raw_value / 65535) * pcf_in_0.reference_voltage

print("Pin 0: %0.2fV" % (scaled_value))

Finally we'll set the DAC value to zero and use the ADC to verify that the DAC can go all the way down to 0V/GND

pcf_out.value = 0
raw_value = pcf_in_0.value
scaled_value = (raw_value / 65535) * pcf_in_0.reference_voltage

print("Pin 0: %0.2fV" % (scaled_value))

Example Code

# SPDX-FileCopyrightText: Copyright (c) 2020 Bryan Siepert for Adafruit Industries
# SPDX-License-Identifier: MIT
import time
import board

import adafruit_pcf8591.pcf8591 as PCF
from adafruit_pcf8591.analog_in import AnalogIn
from adafruit_pcf8591.analog_out import AnalogOut

############# AnalogOut & AnalogIn Example ##########################
#
# This example shows how to use the included AnalogIn and AnalogOut
# classes to set the internal DAC to output a voltage and then measure
# it with the first ADC channel.
#
# Wiring:
# Connect the DAC output to the first ADC channel, in addition to the
# normal power and I2C connections
#
#####################################################################
i2c = board.I2C()
pcf = PCF.PCF8591(i2c)

pcf_in_0 = AnalogIn(pcf, PCF.A0)
pcf_out = AnalogOut(pcf, PCF.OUT)

while True:

    print("Setting out to ", 65535)
    pcf_out.value = 65535
    raw_value = pcf_in_0.value
    scaled_value = (raw_value / 65535) * pcf_in_0.reference_voltage

    print("Pin 0: %0.2fV" % (scaled_value))
    print("")
    time.sleep(1)

    print("Setting out to ", 32767)
    pcf_out.value = 32767
    raw_value = pcf_in_0.value
    scaled_value = (raw_value / 65535) * pcf_in_0.reference_voltage

    print("Pin 0: %0.2fV" % (scaled_value))
    print("")
    time.sleep(1)

    print("Setting out to ", 0)
    pcf_out.value = 0
    raw_value = pcf_in_0.value
    scaled_value = (raw_value / 65535) * pcf_in_0.reference_voltage

    print("Pin 0: %0.2fV" % (scaled_value))
    print("")
    time.sleep(1)

This guide was first published on Jul 13, 2020. It was last updated on Jul 13, 2020.

This page (Python & CircuitPython) was last updated on Apr 15, 2021.

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