In this article we connect a LTR390 UV Light Sensor to an Adafruit Feather M0 running Circuitpython
Sensor Information
This sensor converts light intensity to a digital output signal capable of direct I2C interface.
It provides a linear ALS response over a wide dynamic range, and is well suited to applications under high ambient brightness.
The sensor has a programmable interrupt with hysteresis to response to events and that removes the need to poll the sensor for a reading which improves system efficiency.
This CMOS design and factory-set one time trimming capability ensure minimal sensor-to-sensor variations forease of manufacturability to the end customers.
Features
I2C interface capable of Standard mode @100kHz or Fast mode @400kHz communication; 1.8V logic compatible
Ambient Light / Ultraviolet light(UVS)Technology in one ultra-small 2x2mm ChipLED package
Very low power consumption with sleep mode capability
Operating voltage ranges: 1.7V to 3.6V
Operating temperature ranges: -40 to +85 ºC
Built-in temperature compensation circuit
Programmable interrupt function for ALS , UVS with upper and lower thresholds
RoHS andHalogen free compliant
UVS/ALS Features
- 13 to 20 bits effective resolution
- Wide dynamic range of 1:18,000,000 with linear response
- Close to human eye spectral response
- Automatic rejection for 50Hz/60Hz lighting flicker
This is the sensor that I bought
Parts Required
The sensor you can pick up in the $6 price range – you can connect to the sensor using a standard header the classic dupont style jumper wire.
I used a Qwiic cable – since a few sensors seem to use these but this is optional
| Name | Link |
| Adafruit Feather M0 Express | Amazon link
|
| LTR390 | Adafruit LTR390 UV Light Sensor – Stemma QT/Qwiic |
| Connecting cables | Aliexpress product link |
Schematic/Connection
I used the Adafruit LTR390 sensor and in this case used the Stemma connection
For the STEMMA QT cables, it uses the Qwiic convention:
Black for GND
Red for V+
Blue for SDA
Yellow for SCL
So color coded for ease of use, this layout shows a connection to the module
feather and LTR390
Code Example
I used Mu for development
The following is based on a library , I copied the adafruit_LTR390.mpy library for this device to the lib folder on my Feather M0 Express – https://circuitpython.org/libraries
This is the basic example which comes with the library
[codesyntax lang=”python”]
import time
import board
import adafruit_ltr390
i2c = board.I2C()
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)
[/codesyntax]
Output
Here is what I saw in Mu REPL window
UV: 1 Ambient Light: 71
UVI: 0.0417391 Lux: 56.8
UV: 0 Ambient Light: 70
UVI: 0.0 Lux: 53.6
UV: 0 Ambient Light: 54
UVI: 0.0 Lux: 0.8
UV: 0 Ambient Light: 1
UVI: 0.0 Lux: 0.8
UV: 0 Ambient Light: 65
UVI: 0.0 Lux: 53.6
Links
