Adafruit LTR390 UV Sensor - Qwiic

The LTR390 is one of the few low-cost UV sensors available, and it's a pretty nice one! With both ambient light and UVA sensing with a peak spectral response between 300 and 350nm. You can use it for measuring how much sun you can get before needing to covering up.

Unlike the Si1145, this sensor will not give you UV Index readings. However, the Si1145 does UV Index approximations based on light level not true UV sensing. The LTR-390, in contrast, does have a real light sensor in the UV spectrum. It's also got a much much simpler I2C interface so you can run it on the Arduino or Python microcontrollers/microcomputers with ease. Unlike the GUVA analog sensor, the biasing and ADC is all internal so you don't need an ADC.



To make using it as easy as possible, Adafruit have put the LTR390 on a breakout PCB in the Stemma QT/Qwiic form factor. You can either use a breadboard or the SparkFun qwiic compatible STEMMA QT connectors, and compatibility with 5V voltage levels as commonly found on Arduinos, as well as 3.3V logic used by many other boards like the Raspberry Pi.

Product Video

Quick Spec

• Chip: LTR390
• Measurement Range
• ALS: 500 nm to 600 nm
• UVA: 300 nm to 350 nm
• Supply Voltage: 3V to 5 VDC
• Communication Interface: I2C
• Interface Address: 0x53
• Dimensions: 25.8 x 18mm
• Net Weight: 4g

Pinout

• VIN - power supply pin with voltage range from 3 V to 5 V DC
• 3Vo - supply pin with voltage 3,3 V
• GND - system ground
• SCL - I2C logic pin, communication interface clock line pin
• SDA - I2C logic pin, communication interface data line pin
• INT - main interrupt pin, can be configured according to individual needs

Wiring Diagram

Sample Code

/*************************************************** 
  This is an example for the LTR390 UV Sensor

  Designed specifically to work with the LTR390 UV sensor from Adafruit
  ----> https://www.adafruit.com

  These sensors use I2C to communicate, 2 pins are required to  
  interface
 ****************************************************/
 
#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.print(ltr.readUVS());
  }
  
  delay(100);
}

Resources

• Product Page
• Product Wiki
• LTR390 Datasheet

Shipping List

• 1 x Adafruit LTR390 UV Sensor - Qwiic