I have wired it exactly as directed in this page: Arduino Playground - PhotoResistor. I am taking the average of 4 values per 2 seconds to smooth any big fluctuations in light. Here is my code:
int lightPin = 5; //define a pin for Photo resistor
const int reads = 4;
float light[reads];
float lightTot = 0;
float lightAvg = 0;
void setup()
{
Serial.begin(9600); //Begin serial communcation
for (int i = 0; i < reads; i++){
light[i] = 0; }
}
void loop()
{
lightTot = 0;
for (int i = 0; i < reads; i++){
light[i] = analogRead(lightPin);
Serial.println(light[i]);
lightTot = lightTot + light[i];
delay(500);
}
lightAvg = lightTot / reads;
Serial.println("Total");
Serial.println(lightTot);
Serial.println("Avg");
Serial.println(lightAvg);
Serial.println();
}
I have tried a range of resistors (100K, 10K, 2.2K, and 1K). However, I return either zeros, or inconsistent values that jump around (including zeros). Any suggestions or ideas would be appreciated. Thank you.
-Dave
A photo diode is not a photo resistor, not even slightly!
Two ways to use a photo diode:
Place a large value resistor across it (100k to 10M range?) and measure the forward voltage. This mode is like a photo-voltaic cell
Have it reverse biased and measure the photocurrent - this is the closest to the photoresistor circuit, but again the resistor may need to be a large value in low light. Some photodiodes are optimized for high-speed operation in this mode for communications.
UPDATED: Previous posting here was based off a wiring mistake. Please disregard if already viewed.
@MarkT: Yes I understand, I was just using that link as an example of the circuit rather than attempting to draw it out here. I have read multiple other posts which utilize that same circuit for a photodiode. Ill just assume they were incorrect. With your suggested reverse bias configuration, my average values are much more consistent (configuration like in Fig 2 here: http://goo.gl/7kL5H; Vcc = 5V, Rl = 100K).
If I want to change the sensitivity of the diode to higher or lower light, I would decrease or increase (respectively) the resistor value, correct? What if I need to measure a very broad range of light levels? Do I go with something in the middle?
My goal is to measure light levels throughout the day inside of a plant growth chamber which is shaded to approx 15% full sunlight.
Hey guys! I have the same question. I'm using a BPW21R photo-diode to measure the quantity of light in an optical fiber. I'm using the photo-diode with an Arduino Nano 3.0. I've tried to use the same scheme above but I got some wrong numbers. Does anyone can help me with that? I used resistors of 2K, 10K 100K and when I open the serial monitor the result is 0. When I take the resistor off the value showed is 1023.
It would help if you actually used the symbol for a photo diode so we could see which way round you have it.
Basically a photo diode usually needs an amplifier.
I used one in this project:- http://www.thebox.myzen.co.uk/Hardware/Sneak_Thief.html
