Adafruit AS7331 UV / UVA / UVB / UVC Sensor

Three types of UV, measured over I2C

by Liz Clark

published March 10, 2026, last edited April 28, 2026

posted in Adafruit Products Sensors/ Light Arduino Compatibles CircuitPython STEMMA

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Product guide

Arduino

Using the AS7331 UV sensor with Arduino involves wiring up the sensor to your Arduino-compatible microcontroller, installing the Adafruit_AS7331 library and running the provided example code.

Wiring

Wire as shown for a 5V board like an Uno. If you are using a 3V board, like an Adafruit Feather, wire the board's 3V pin to the AS7331 VIN.

Here is an Adafruit Metro wired up to the AS7331 using the STEMMA QT connector:

Board 5V to breakout STEMMA VIN (red wire)
Board GND to breakout STEMMA GND (black wire)
Board SCL to breakout STEMMA SCL (yellow wire)
Board SDA to breakout STEMMA SDA (blue wire)

Here is an Adafruit Metro wired up using a solderless breadboard:

Board 5V to breakout VIN (red wire)
Board GND to breakout GND (black wire)
Board SCL to breakout SCL (yellow wire)
Board SDA to breakout SDA (blue wire)

Library Installation

You can install the Adafruit AS7331 library for Arduino using the Library Manager in the Arduino IDE.

Click the Manage Libraries ... menu item, search for Adafruit AS7331, and select the Adafruit AS7331 library:

If asked about dependencies, click "Install all".

If the "Dependencies" window does not come up, then you already have the dependencies installed.

If the dependencies are already installed, you must make sure you update them through the Arduino Library Manager before loading the example!

Example Code

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#include <Adafruit_AS7331.h>

Adafruit_AS7331 as7331;

void setup() {
  Serial.begin(115200);
  while (!Serial) delay(10);

  Serial.println("AS7331 Full Test");
  Serial.println("================");

  if (!as7331.begin()) {
    Serial.println("AS7331 not found!");
    while (1) delay(10);
  }

  // Print device info
  Serial.print("Device ID: 0x");
  Serial.println(as7331.getDeviceID(), HEX);

  // Configure sensor
  as7331.powerDown(true);

  as7331.setGain(AS7331_GAIN_4X);
  as7331.setIntegrationTime(AS7331_TIME_64MS);
  as7331.setMeasurementMode(AS7331_MODE_CONT);
  as7331.setClockFrequency(AS7331_CLOCK_1024MHZ);
  as7331.setBreakTime(25); // 200µs
  as7331.setStandby(false);
  as7331.setReadyPinOpenDrain(false); // Push-pull

  // Print current configuration
  Serial.println("\nConfiguration:");
  Serial.print("  Gain: ");
  Serial.println(as7331.getGain());
  Serial.print("  Integration Time: ");
  Serial.println(as7331.getIntegrationTime());
  Serial.print("  Measurement Mode: ");
  Serial.println(as7331.getMeasurementMode());
  Serial.print("  Clock Frequency: ");
  Serial.println(as7331.getClockFrequency());
  Serial.print("  Break Time: ");
  Serial.println(as7331.getBreakTime());
  Serial.print("  Standby: ");
  Serial.println(as7331.getStandby());
  Serial.print("  READY Pin Open-Drain: ");
  Serial.println(as7331.getReadyPinOpenDrain());
  Serial.print("  Edge Count: ");
  Serial.println(as7331.getEdgeCount());

  // Start measurements
  as7331.powerDown(false);

  Serial.println("\nStarting continuous readings...\n");
}

void loop() {
  // Read raw counts
  uint16_t uva, uvb, uvc;
  if (as7331.readAllUV(&uva, &uvb, &uvc)) {
    Serial.print("Raw - UVA: ");
    Serial.print(uva);
    Serial.print("  UVB: ");
    Serial.print(uvb);
    Serial.print("  UVC: ");
    Serial.println(uvc);
  }

  // Read in µW/cm²
  float uva_uw, uvb_uw, uvc_uw;
  if (as7331.readAllUV_uWcm2(&uva_uw, &uvb_uw, &uvc_uw)) {
    Serial.print("µW/cm² - UVA: ");
    Serial.print(uva_uw, 2);
    Serial.print("  UVB: ");
    Serial.print(uvb_uw, 2);
    Serial.print("  UVC: ");
    Serial.println(uvc_uw, 2);
  }

  // Temperature
  Serial.print("Temperature: ");
  Serial.print(as7331.readTemperature(), 1);
  Serial.println(" °C");

  // Status
  uint8_t status = as7331.getStatus();
  Serial.print("Status: 0x");
  Serial.print(status, HEX);
  if (as7331.hasNewData()) Serial.print(" [NEW]");
  if (as7331.hasOverflow()) Serial.print(" [OVERFLOW]");
  if (as7331.hasLostData()) Serial.print(" [LOST]");
  Serial.println();

  Serial.println();
  delay(1000);
}

#include <Adafruit_AS7331.h>

Adafruit_AS7331 as7331;

void setup() {
  Serial.begin(115200);
  while (!Serial) delay(10);

  Serial.println("AS7331 Full Test");
  Serial.println("================");

  if (!as7331.begin()) {
    Serial.println("AS7331 not found!");
    while (1) delay(10);
  }

  // Print device info
  Serial.print("Device ID: 0x");
  Serial.println(as7331.getDeviceID(), HEX);

  // Configure sensor
  as7331.powerDown(true);

  as7331.setGain(AS7331_GAIN_4X);
  as7331.setIntegrationTime(AS7331_TIME_64MS);
  as7331.setMeasurementMode(AS7331_MODE_CONT);
  as7331.setClockFrequency(AS7331_CLOCK_1024MHZ);
  as7331.setBreakTime(25); // 200µs
  as7331.setStandby(false);
  as7331.setReadyPinOpenDrain(false); // Push-pull

  // Print current configuration
  Serial.println("\nConfiguration:");
  Serial.print("  Gain: ");
  Serial.println(as7331.getGain());
  Serial.print("  Integration Time: ");
  Serial.println(as7331.getIntegrationTime());
  Serial.print("  Measurement Mode: ");
  Serial.println(as7331.getMeasurementMode());
  Serial.print("  Clock Frequency: ");
  Serial.println(as7331.getClockFrequency());
  Serial.print("  Break Time: ");
  Serial.println(as7331.getBreakTime());
  Serial.print("  Standby: ");
  Serial.println(as7331.getStandby());
  Serial.print("  READY Pin Open-Drain: ");
  Serial.println(as7331.getReadyPinOpenDrain());
  Serial.print("  Edge Count: ");
  Serial.println(as7331.getEdgeCount());

  // Start measurements
  as7331.powerDown(false);

  Serial.println("\nStarting continuous readings...\n");
}

void loop() {
  // Read raw counts
  uint16_t uva, uvb, uvc;
  if (as7331.readAllUV(&uva, &uvb, &uvc)) {
    Serial.print("Raw - UVA: ");
    Serial.print(uva);
    Serial.print("  UVB: ");
    Serial.print(uvb);
    Serial.print("  UVC: ");
    Serial.println(uvc);
  }

  // Read in µW/cm²
  float uva_uw, uvb_uw, uvc_uw;
  if (as7331.readAllUV_uWcm2(&uva_uw, &uvb_uw, &uvc_uw)) {
    Serial.print("µW/cm² - UVA: ");
    Serial.print(uva_uw, 2);
    Serial.print("  UVB: ");
    Serial.print(uvb_uw, 2);
    Serial.print("  UVC: ");
    Serial.println(uvc_uw, 2);
  }

  // Temperature
  Serial.print("Temperature: ");
  Serial.print(as7331.readTemperature(), 1);
  Serial.println(" °C");

  // Status
  uint8_t status = as7331.getStatus();
  Serial.print("Status: 0x");
  Serial.print(status, HEX);
  if (as7331.hasNewData()) Serial.print(" [NEW]");
  if (as7331.hasOverflow()) Serial.print(" [OVERFLOW]");
  if (as7331.hasLostData()) Serial.print(" [LOST]");
  Serial.println();

  Serial.println();
  delay(1000);
}

View on GitHub

Upload the sketch to your board and open up the Serial Monitor (Tools -> Serial Monitor) at 115200 baud. You should see that the sketch has found your connected AS7331 sensor. The default settings are written to the sensor. Then, continuous readings start. You'll see the UVA, UVB, UVC and temperature readings printed to the Serial Monitor every second.