Upload the following code to your FLORA, ensuring you have the UV index sensor library installed properly (you should if you tested your sensor in the last step). This code is suited well for testing your complete circuit indoors, near a window. The UV index threshold is set very low (0.05, achievable by pointing it towards an open window), with a reminder interval of ten seconds. You can also open up serial monitor while it's running to check out the readings and timer.
/*************************************************** 
  Sunscreen reminder hat using the Si1145 UV/IR/Visible Light Sensor
  visit https://learn.adafruit.com/sunscreen-reminder-hat for full tutorial
  
  contains Super Mario Bros theme composed for piezo by Tiago Gala: http://therandombit.wordpress.com/2011/11/21/arduino-piezo-speaker-super-mario/
  
  Written by Becky Stern for Adafruit Industries.  
  BSD license, all text above must be included in any redistribution
 ****************************************************/
 
#include <Wire.h>
#include "Adafruit_SI1145.h"

Adafruit_SI1145 uv = Adafruit_SI1145();

//tones for reminder tune
#define toneC    1911
#define toneC1    1804
#define toneD    1703
#define toneEb    1607
#define toneE    1517
#define toneF    1432
#define toneF1    1352
#define toneG    1276
#define toneAb    1204
#define toneA    1136
#define toneBb    1073
#define toneB    1012
#define tonec       955
#define tonec1      902
#define toned       851
#define toneeb      803
#define tonee       758
#define tonef       716
#define tonef1      676
#define toneg       638
#define toneab      602
#define tonea       568
#define tonebb      536
#define toneb       506
#define tonep       0 
int speaker = 1; // piezo wired to FLORA TX


uint32_t sinceTime;
uint32_t markerTime;
boolean shouldChime = false;
float UVindex;
float UVthreshold = 0.05;
uint32_t reapplyInterval = 10000; // 15 minutes = 900000 milliseconds. One hour = 3600000 milliseconds. Two hours = 7200000 milliseconds

void setup() {
  pinMode(speaker, OUTPUT);
  Serial.begin(9600);
  Serial.println("Adafruit SI1145 test");
  if (! uv.begin()) {
    Serial.println("Didn't find Si1145");
    while (1);
  }
  Serial.println("OK!");
}

void loop() {
  Serial.println("===================");
  UVindex = uv.readUV(); 
  UVindex /= 100.0; // the index is multiplied by 100 so to get the integer index, divide by 100!  
  Serial.print("UV: ");  Serial.println(UVindex);
  Serial.print("Seconds until next alert: ");  Serial.println((reapplyInterval-sinceTime)/1000);
  delay(1000);
  
  sinceTime = millis()-markerTime;
  
  if (UVindex > UVthreshold && shouldChime){ //only chime when we are currently outside
    chime();
    Serial.println("===================");
    Serial.println("CHIME");
    shouldChime = false;
    resetTimer();
  }
  if (sinceTime > reapplyInterval) { //check to see if we've exceeded the time limit
    shouldChime = true;
    resetTimer; 
  }
  
}

void resetTimer(){
  markerTime = millis();
  sinceTime = 0;
}

void chime(){
int melody[] = {tonec, toneG, toneE, toneA, toneB, toneBb, toneA, toneG, tonee, toneg, tonea, tonef, toneg, tonee, tonec, toned, toneB};
int rhythm[] = {18, 18, 18, 12, 12, 6, 12, 8, 8, 8, 12, 6, 12, 12, 6, 6, 6};
long vel = 20000;

for (int i=0; i<17; i++) {
    int note = melody[i];
    int tempo = rhythm[i];
 
    long tvalue = tempo * vel;
 
    //tocar(note, tvalue);
    long tempo_progress = 0;
  while (tempo_progress < tvalue) {
    digitalWrite(speaker, HIGH);
    delayMicroseconds(note / 2);
 
    digitalWrite(speaker, LOW);
    delayMicroseconds(note/2);	 
    tempo_progress += note;
  }
 
    delayMicroseconds(1000);
  }

}
If everything's working properly, modify these two lines:
float UVthreshold = 0.05;
long reapplyInterval = 10000; // 15 minutes = 900000 milliseconds. One hour = 3600000 milliseconds. Two hours = 7200000 milliseconds
to reflect the UV index you'd like to sound the alarm, and how often you'd like a reminder.
This guide was first published on Jul 23, 2014. It was last updated on Nov 19, 2018. This page (Code) was last updated on May 04, 2015.