UltraV: A Portable UV-Index Meter

1    /* 
2 Fabio Marzocca @ 2018
3 Analog to digital conversions rely  completely on VCC. We assume
4 this is 5V but if the board is powered from USB  this may be as high as 5.25V or as low as 4.75V:
5 http://en.wikipedia.org/wiki/USB#Power  Because of this unknown window it makes the ADC fairly inaccurate
6 in most cases.  To fix this, we use the very accurate onboard 3.3V reference (accurate within 1%).  So by doing an
7 ADC on the 3.3V pin (A1) and then comparing this against the  reading from the sensor we can extrapolate
8 a true-to-life reading no matter  what VIN is (as long as it's above 3.4V).
9
10v. 2.0.0 - July 2018
11   - moved  from 16x2 LCD to OLED
12v. 2.0.1 - Sept 2018
13   - changed read battery function
14*/
15
16#include  <Arduino.h>
17#include <U8g2lib.h>
18#include <Wire.h>
19
20U8G2_SSD1306_128X64_NONAME_F_SW_I2C  u8g2(U8G2_R0, /* clock=*/ SCL, /* data=*/ SDA, /* reset=*/ U8X8_PIN_NONE);   //  All Boards without Reset of the Display
21
22#define FIRST_ROW_Y 16
23#define  FIRST_ROW_X 16
24#define BOX_H 38
25
26//Hardware pin definitions
27const int  UVOUT = A0; //Output from the sensor
28const int REF_3V3 = A1; //3.3V power on  the Arduino board
29const int VBATT = A2; //Battery voltage
30
31float maxUV  = 0; //Max UV index read
32
33
34void setup()
35{ 
36  pinMode(UVOUT, INPUT);
37  pinMode(REF_3V3, INPUT);
38  pinMode(VBATT, INPUT);
39 
40  u8g2.begin();
41
42}
43
44void  loop()
45{
46  u8g2.firstPage();
47  do {
48    int uvLevel = averageAnalogRead(UVOUT);
49    int refLevel = averageAnalogRead(REF_3V3);
50
51    //Use the 3.3V power pin  as a reference to get a very accurate output value from sensor
52    float outputVoltage  = 3.3 / refLevel * uvLevel;
53
54    float uvIntensity = mapfloat(outputVoltage,  0.99, 2.6, 0.0, 15.0); //Convert the voltage to a UV intensity level
55
56    readBattery();
57    if (maxUV < uvIntensity) {
58        maxUV = uvIntensity;
59      }
60    u8g2.drawFrame(0,FIRST_ROW_Y+1,128,BOX_H);
61    u8g2.setFont(u8g2_font_logisoso18_tf);
62
63    //Instant UV
64    u8g2.setCursor(10,40);
65    u8g2.print(uvIntensity);
66    //UV Max
67    u8g2.setCursor(70,40);
68    u8g2.print(maxUV);
69
70    u8g2.setFont(u8g2_font_u8glib_4_tf);
71    u8g2.setCursor(10,52); u8g2.print(F("INSTANT"));
72    u8g2.setCursor(75,52); u8g2.print(F("MAXIMUM"));
73
74    showUVCategory();
75    u8g2.setCursor(88,64); u8g2.print(F("F.Marzocca"));
76    
77   } while  ( u8g2.nextPage() );
78  delay(200);
79}
80
81// Reads maxUV and prints the  UV category
82void showUVCategory() {
83  char strCat[12];
84
85  byte categ  = (byte)(maxUV+0.5);  //round up
86  if ((categ >= 0) && (categ < 3)) {
87    strcpy(strCat,  "LOW"); 
88  } else if ((categ >= 3) && (categ < 6)) {
89    strcpy(strCat,  "MODERATE");
90  } else if ((categ >= 6) && (categ < 8)) {
91    strcpy(strCat,  "HIGH !");
92  } else if ((categ >= 8) && (categ < 10)) {
93     strcpy(strCat,  "VERY HIGH!");
94  } else if (categ >= 11) {
95    strcpy(strCat, "EXTREME!");
96  }
97  
98   u8g2.setCursor(0,64);
99   u8g2.print(strCat);
100  
101}
102
103//Takes  an average of readings on a given pin
104//Returns the average
105int averageAnalogRead(int  pinToRead)
106{
107  byte numberOfReadings = 16;
108  unsigned int runningValue  = 0; 
109
110  for(int x = 0 ; x < numberOfReadings ; x++)
111    runningValue +=  analogRead(pinToRead);
112  runningValue /= numberOfReadings;
113
114  return(runningValue);  
115}
116
117//The Arduino Map function but for floats
118//From: http://forum.arduino.cc/index.php?topic=3922.0
119float  mapfloat(float x, float in_min, float in_max, float out_min, float out_max)
120{
121  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
122}
123
124void  readBattery() {
125   long battery = readBattVcc(); 
126   long VccMin = 2300; //Battery  minimum voltage read on Vcc
127   byte batteryBar; //Battery progress bar
128   int  barStep = 140; //step for battery progress bar (235)
129
130   batteryBar = (battery  - VccMin)/barStep;
131   
132       //battery icon
133    u8g2.setFont(u8g2_font_open_iconic_embedded_2x_t);
134    u8g2.drawGlyph(1, FIRST_ROW_Y, 73 );
135    
136    // battery status cursor
137    u8g2.setFont(u8g2_font_open_iconic_play_1x_t);
138    for (byte i=1; i<=batteryBar;  i++) {
139       u8g2.drawGlyph( 128-9*i,FIRST_ROW_Y-4,75);
140    }
141    
142    // battery voltage
143    u8g2.setFont(u8g2_font_freedoomr10_tu);
144    u8g2.setCursor(25,  FIRST_ROW_Y);
145    u8g2.print(float(battery)/1000, 3);
146 
147}
148
149
150long  readBattVcc()
151{
152    int sum=0;
153    int sample_count=0;
154    long voltage=  0;
155    #define NUM_SAMPLES 10
156    // take a number of analog samples and add  them up
157    while (sample_count < NUM_SAMPLES) {
158        sum += analogRead(VBATT);
159        sample_count++;
160        delay(2);
161    }
162        // calculate the  voltage
163    // use 5000 for a 5.0V ADC reference voltage
164    // 5020V is the  calibrated reference voltage (in millivolts) for my project
165    voltage = ((long)sum  / (long)NUM_SAMPLES * 5020) / 1024.0;
166    return voltage; //Vbattery in millivolts
167}
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