Microbit and LTR390 UV Light Sensor Arduino example

In this article we look at another UV Light Sensor – this time its the LTR390 and we will connect it to our Microbit and see what it can do

First lets take a look at the sensor in question, this is from the datasheet

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 Chip LED package
Very low power consumption with sleep mode capability
Operating voltage ranges: 1.7V to 3.6V
Operating temperature ranges: -40 to +85 ┬║C
Built-in temperature compensation circuit
Programmable interrupt function for ALS , UVS with upper and lower thresholds
RoHS and Halogen 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

Once again for ease of use I connect an expansion board to the microbit, I feel this makes it easier to connect to a sensor like the one pictured above using connecting wire

Name Link
Microbit Offical Microbit V2 Development Board
LTR390 Adafruit Industries Adafruit LTR390 UV Light Sensor – Stemma QTQwiic
Connecting wire Free shipping Dupont line 120pcs 20cm male to male + male to female and female to female jumper wire
expansion board micro: bit expansion board

Schematic/Connection

The layout below shows a Microbit, I used a Microbit v1

Black for GND
Red for V+
Blue for SDA
Yellow for SCL

microbit and ltr390 layout
microbit and ltr390 layout

Code Example

This sensor uses a couple of libraries, both of which can be installed using the library manager. if you search for the LTR390 one first and you are using a newer version of the Arduino IDE it will install the other one as well – which makes things a bit easier.

You need the Adafruit library for the https://github.com/adafruit/Adafruit_LTR390

You also need an I2C support library from the same folks for the library above to work and that is available from – https://github.com/adafruit/Adafruit_BusIO

This is the simple test example

[codesyntax lang=”cpp”]

#include "Adafruit_LTR390.h"

Adafruit_LTR390 ltr = Adafruit_LTR390();

void setup() {
  Serial.begin(115200);
  Serial.println("Adafruit LTR-390 test");

  if ( ! ltr.begin() ) {
    Serial.println("Couldn't find LTR sensor!");
    while (1) delay(10);
  }
  Serial.println("Found LTR sensor!");

  ltr.setMode(LTR390_MODE_UVS);
  if (ltr.getMode() == LTR390_MODE_ALS) {
    Serial.println("In ALS mode");
  } else {
    Serial.println("In UVS mode");
  }

  ltr.setGain(LTR390_GAIN_3);
  Serial.print("Gain : ");
  switch (ltr.getGain()) {
    case LTR390_GAIN_1: Serial.println(1); break;
    case LTR390_GAIN_3: Serial.println(3); break;
    case LTR390_GAIN_6: Serial.println(6); break;
    case LTR390_GAIN_9: Serial.println(9); break;
    case LTR390_GAIN_18: Serial.println(18); break;
  }

  ltr.setResolution(LTR390_RESOLUTION_16BIT);
  Serial.print("Resolution : ");
  switch (ltr.getResolution()) {
    case LTR390_RESOLUTION_13BIT: Serial.println(13); break;
    case LTR390_RESOLUTION_16BIT: Serial.println(16); break;
    case LTR390_RESOLUTION_17BIT: Serial.println(17); break;
    case LTR390_RESOLUTION_18BIT: Serial.println(18); break;
    case LTR390_RESOLUTION_19BIT: Serial.println(19); break;
    case LTR390_RESOLUTION_20BIT: Serial.println(20); break;
  }

  ltr.setThresholds(100, 1000);
  ltr.configInterrupt(true, LTR390_MODE_UVS);
}

void loop() 
{
  if (ltr.newDataAvailable()) 
  {
      Serial.print("UV data: "); 
      Serial.println(ltr.readUVS());
  }
  
  delay(100);
}

[/codesyntax]

Output

Open the serial monitor and you should see something like this

UV data: 0
UV data: 0
UV data: 0
UV data: 0
UV data: 0
UV data: 0
UV data: 0

Links

Datasheet

 

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