It's easy to use the LTR390 with Python or CircuitPython, and the Adafruit CircuitPython LTR390 module. This module allows you to easily write Python code that reads uv and ambient light from the LTR390 sensor.

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

First wire up a LTR390 to your board exactly as shown below. Here's an example of wiring a Feather M4 to the sensor with I2C using one of the handy STEMMA QT connectors:

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

You can also use the standard 0.100" pitch headers to wire it up on a breadboard:

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

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 STEMMA QT connector:

  • Pi 3V to sensor VCC (red wire)
  • Pi GND to sensor GND (black wire)
  • Pi SCL to sensor SCL (yellow wire)
  • Pi SDA to sensor SDA (blue wire)

Finally here is an example of how to wire up a Raspberry Pi to the sensor using a solderless breadboard

  • Pi 3V to sensor VCC (red wire)
  • Pi GND to sensor GND (black wire)
  • Pi SCL to sensor SCL (yellow wire)
  • Pi SDA to sensor SDA (blue wire)

CircuitPython Installation of LTR390 Library

You'll need to install the Adafruit CircuitPython LTR390 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_LTR390.mpy file and the adafruit_register and adafruit_bus_device folders copied over.

When done, your CIRCUITPY drive should look like this:

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

Python Installation of LTR390 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-ltr390

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 sensor we'll initialize it and read the UV and ambient light measurements from the board's Python REPL.

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

import board
import busio
import adafruit_ltr390

i2c = busio.I2C(board.SCL, board.SDA)

ltr = adafruit_ltr390.LTR390(i2c)

Now you're ready to read values from the sensor using these properties:

  • uvs - The raw UV light measurement.
  • light - The raw ambient light measurement.
  • uvi - The calculated UV Index value.
  • lux - The calculated Lux ambient light value.
print("UV:", ltr.uvs, "\t\tAmbient Light:", ltr.light)
print("UV Index:", ltr.uvi, "\t\tLux:", ltr.lux)

Example Code

# SPDX-FileCopyrightText: 2021 by Bryan Siepert, written for Adafruit Industries
#
# SPDX-License-Identifier: Unlicense
import time
import board
import busio
import adafruit_ltr390

i2c = busio.I2C(board.SCL, board.SDA)

ltr = adafruit_ltr390.LTR390(i2c)

while True:
    print("UV:", ltr.uvs, "\t\tAmbient Light:", ltr.light)
    print("UVI:", ltr.uvi, "\t\tLux:", ltr.lux)
    time.sleep(1.0)

This guide was first published on Dec 29, 2020. It was last updated on Dec 29, 2020.

This page (Python & CircuitPython) was last updated on Apr 20, 2021.

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