ArduMeter - Arduino Incident Light Meter

1/*
2  ArduMeter (Arduino incident light meter) version 2
3  by Alan  Wang
4
5  BH1750/BH1750FVI digital light intensity sensor:
6  Library: https://github.com/claws/BH1750
7  VCC -> 3.3V
8  GND -> GND
9  SDA -> pin A4
10  SCL -> pin A5
11  ADD ->  (none)
12
13  0.96" SSD1306 OLED 128x64 display:
14  Library: https://github.com/greiman/SSD1306Ascii
15  VCC -> 3.3V
16  GND -> GND
17  SDA -> pin A4
18  SCL -> pin A5
19
20  1x  push button
21  leg 1 -> pin D2
22  leg 2 -> GND
23
24  2x 10 kOhms potentiometer  (knob)
25  leg 1 -> 3.3V
26  leg 2 (middle) -> pin A0/A1 (max analog signal about  730-740)
27  leg 3 -> GND
28
29   ------------------------------ */
30
31//  Set this to true if you wish to get "standard" shutter settings
32#define STANRARD_SHUTTER_SPEED  false
33
34// Calibration constant (C) for incident light meters.
35// see  https://en.wikipedia.org/wiki/Light_meter#Calibration_constants
36#define INCIDENT_CALIBRATION    330
37
38// Max analog readings from potentiometers. Change it only if you  are
39// using different input voltage or potentiometers that are not 10K.
40#define  KNOB_MAX_ANALOG_READING 740
41
42// Define pins
43#define BUTTON_PIN              2  // D2
44#define KNOB_APERTURE_PIN       0  // A0
45#define KNOB_ISO_PIN            1  // A1
46
47// Pre-defined aperture and ISO settings. Modify them for your own  preference.
48// Elements in the array have to be sorted from min to max.
49const  double APERATURE_TABLE[]  = {1.0, 1.4, 1.8, 2.0, 2.8, 3.5, 4.0, 4.5, 5.6, 6.3, 8.0,  11.0, 12.7, 16.0, 22.0, 32.0};
50const int ISO_TABLE[]           = {6, 12, 25,  50, 100, 160, 200, 400, 800, 1600, 3200};
51
52// The "shutterspeed table" array  is used when STANRARD_SHUTTER_SPEED is set to true.
53// 1/2 (0.5) seconds is expressed  as 2, and 2 seconds is expressed as -2.
54double SHUTTERSPEED_TABLE[]     = {-60,  -30, -15, -8, -4, -2, -1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000, 2000, 4000};
55
56//  If you are using older cameras which have different shutter speed settings,
57//  you can switch to the folloing array:
58// double SHUTTERSPEED_TABLE[]    = {-1,  2, 5, 10, 25, 50, 100, 250, 500, 1000};
59
60/* ------------------------------  */
61
62#include <math.h>
63#include <Wire.h>
64#include <BH1750.h>
65#include  "SSD1306Ascii.h"
66#include "SSD1306AsciiAvrI2c.h"
67
68BH1750 bh1750;
69SSD1306AsciiAvrI2c  oled;
70
71bool started = false;
72int EV, apertureIndex, apertureIndexOld, isoIndex,  isoIndexOld;
73long lux;
74
75void setup() {
76
77  // initialize serial port
78  Serial.begin(9600);
79  Wire.begin();
80
81  // prepare the shutterspeed table  array if needed
82  if (STANRARD_SHUTTER_SPEED) {
83    for (int i = 0; i < (sizeof(SHUTTERSPEED_TABLE)  / sizeof(double)); i++) {
84      if (SHUTTERSPEED_TABLE[i] < 0) {
85        SHUTTERSPEED_TABLE[i]  = 1 / abs(SHUTTERSPEED_TABLE[i]);
86      }
87    }
88  }
89
90  // setup button
91  pinMode(BUTTON_PIN, INPUT_PULLUP);
92
93  // set the BH1750 in BH1750_ONE_TIME_HIGH_RES_MODE_2
94  bh1750.begin(0x21);
95
96  // "initialize" BH1750 by using it once
97  bh1750.readLightLevel();
98
99  // initialize OLED
100  oled.begin(&Adafruit128x64, 0x3c);
101  oled.setFont(System5x7);
102  oled.set2X();
103
104  Serial.println("ArduMeter (Arduino incident light meter  for camera) READY:");
105  Serial.println("- Press button to measure light.");
106  Serial.println("- Turn knobs to change aperature/ISO.");
107
108  oled.clear();
109  oled.println("ArduMeter");
110  oled.println("READY");
111  oled.println("press");
112  oled.println("button");
113}
114
115void loop() {
116
117  //read status from  button and potentiometers
118  getKnobIndex();
119
120  if (buttonPressed()) { //measure  light
121    if (!started) started = true;
122    displayExposureSetting(true);
123    delay(150);
124
125  } else { //change aperture/ISO settings
126    if ((apertureIndex  != apertureIndexOld || isoIndex != isoIndexOld) && started) {
127      displayExposureSetting(false);
128      delay(150);
129    }
130  }
131
132  //record potentiometer previous status
133  apertureIndexOld = apertureIndex;
134  isoIndexOld = isoIndex;
135
136  delay(50);
137}
138
139//  read if the button is pressed (pulled low)
140bool buttonPressed() {
141  return  !digitalRead(BUTTON_PIN);
142}
143
144// map knob analog readings to array indexes
145void  getKnobIndex() {
146  apertureIndex = round(map(analogRead(KNOB_APERTURE_PIN), 0,  KNOB_MAX_ANALOG_READING, 0, sizeof(APERATURE_TABLE) / sizeof(float)));
147  isoIndex  = round(map(analogRead(KNOB_ISO_PIN), 0, KNOB_MAX_ANALOG_READING, 0, sizeof(ISO_TABLE)  / sizeof(int)));
148}
149
150// measure/calculate and display exposure settings
151void  displayExposureSetting(bool measureNewEV) {
152
153  double aperature = APERATURE_TABLE[apertureIndex];
154  int iso = ISO_TABLE[isoIndex];
155
156  // measure light level (illuminance) and  get a new lux value
157  if (measureNewEV) {
158    lux = bh1750.readLightLevel();
159    Serial.print("Measured illuminance = ");
160    Serial.print(lux);
161    Serial.println("  lux");
162  }
163
164  //calculate EV
165  EV = log10(lux * iso / INCIDENT_CALIBRATION)  / log10(2);
166
167  if (isfinite(EV)) { //calculate shutter speed if EV is neither  NaN nor infinity
168
169    // calculate shutter speed
170    double shutterspeed  = (pow(2, EV) / pow(aperature, 2));
171
172    // choose standard shutter speed  if needed
173    if (STANRARD_SHUTTER_SPEED) {
174      for (int i = 0; i < (sizeof(SHUTTERSPEED_TABLE)  / sizeof(double)) - 1; i++) {
175        if (shutterspeed >= SHUTTERSPEED_TABLE[i]  && shutterspeed <= SHUTTERSPEED_TABLE[i + 1]) {
176          if (abs(shutterspeed  - SHUTTERSPEED_TABLE[i]) <= abs(shutterspeed) - SHUTTERSPEED_TABLE[i + 1]) {
177            shutterspeed = SHUTTERSPEED_TABLE[i];
178          } else {
179            shutterspeed  = SHUTTERSPEED_TABLE[i + 1];
180          }
181          break;
182        }
183      }
184    }
185
186    // output result to serial port
187    Serial.print("Exposure  settings: EV = ");
188    Serial.print(EV);
189    Serial.print(", ISO = ");
190    Serial.print(iso);
191    Serial.print(", aperture = f/");
192    Serial.print(aperature,  1);
193    Serial.print(", ");
194    Serial.print("shutter speed = ");
195    if (shutterspeed > 1) {
196      Serial.print("1/");
197      Serial.print(shutterspeed);
198    } else {
199      Serial.print((1 / shutterspeed));
200    }
201    Serial.println("s");
202
203    // output result to OLED
204    oled.clear();
205    oled.print("EV: ");
206    oled.println(EV, 1);
207    oled.print("ISO ");
208    oled.println(iso);
209    oled.print("-- f/");
210    oled.println(aperature, 1);
211    oled.print("--  ");
212    if (shutterspeed > 1) {
213      oled.print("1/");
214      oled.print(shutterspeed,  0);
215    } else {
216      oled.print((1 / shutterspeed), 0);
217    }
218    oled.println("s");
219
220  } else {
221    Serial.println("Exposure out of bounds");
222    oled.clear();
223    oled.println("Exposure");
224    oled.println("value");
225    oled.println("out  of");
226    oled.println("bounds");
227  }
228}