Shutter-Speed Measurements for Film Cameras

1
2/* A simple tool to test shutter speed of film cameras to ensure accuracy.
3  *  Built by Cyrus Rupa in 2022.
4 *  
5 *  This system makes use of a simple  trick that LED's can also sense light, (I used a blue one).
6 *  
7 *  **********************************
8  *  ***     How to use   ***
9 *  
10 *  Make the default LED blink circuit. 
11  *  
12 *  1. A0 to 10K ohm resistor -> LED +
13 *  2. LED - to ground
14 *  
15  *  3.  Open the back of the film camera and position the LED behind the shutter  curtain.
16 *  4. Take the lens off it is easy
17 *  5. Place a flashlight shining  into the camera from the other side.
18 *  6. Run the script to get threshold baseline.
19  *  7. Run the script Serial monitor will show you how long each shutter opening  was.
20 *  8. Do a few runs to get an average.  +-5% is about normal.  I have tested  up to 1/1000th with good results.
21 *  
22 *  
23 *  **********************************
24  */
25
26 
27
28int volatile sensorValue; //light level value read by LED
29long  volatile t1;
30long volatile t2;
31int timer;
32
33/* Take a few readings of  the flashlight shining through and adjust this to be the threshold 
34of the LED  seeing the flashlight. */
35int threshold = 390; 
36
37
38void setup() {
39  Serial.begin(9600); // Use to view sensor value
40  pinMode(A0, INPUT); //Change  A0 back to an Analog input pin
41  Serial.println("Shutter Speed Measurement by  Cyrus Rupa");
42
43}
44
45void loop() {
46  sensorValue = analogRead(A0);  //Read LED as a sensor
47
48  /* Turn this on to get baseline for threshold. Comment  out lines below. */
49  // Serial.println(sensorValue); 
50
51  if (sensorValue  > threshold) {
52    t1 = micros();
53    sensorValue = analogRead(A0); //Read  LED as a sensor
54    while (sensorValue > threshold) {
55      sensorValue =  analogRead(A0); //Read LED as a sensor
56    }
57    t2 = micros();
58
59    timer  = (t2 - t1) / 1000;
60    Serial.print("Shutter speed recorded as "); Serial.print(timer);  Serial.println(" milliseconds");
61  }
62}
63