Hi,
I am having trouble reading light intensity with a TAOS light-to-voltage sensor, TSL250r-LF http://www.taosinc.com/getfile.aspx?type=press&file=tsl250r-e30.pdf. The light source that is being measured is an RGB LED controlled by PWM pins 9 (red), 10 (green) and 11 (blue) on an Arduino Mega 2560 board.
The board takes readings from two TSL250 sensors every second, and sends data to serial out. Because the LED is either on or off, depending on the PWM signal duty cycle, the reading from the sensor is a mixture of high and low numbers. When the PWM is set to dim light, the numbers are mostly 0's and a few 1021 (and some random number in-between). When the LED is set to bright light, the numbers are mostly 1021 and a few 0's.
I need the readings to be very steady. The project is a photometer that measures light absorbance.
I know there are ways to smooth the PWM to DC using hardware such as a DAC. It would be nice if a change in the software would resolve the issue.
My question: Would it fix this issue to have the light sensor take a reading only when the PWM signal is high? The frequency is about 500 hz, so the PWM signal changes to high every 2 msec.
The code is below. I deleted most of the non-relevant parts. The lines that trigger the sensor readings are:
// read the analog in values from the 2 sensors:
sensorValue = analogRead(analogInPin);
sensorValue1 = analogRead(analogInPin1);
Could I use an attachInterrupt somehow to delay running these lines until the LED is powered? Or is there a better way?
It would be ideal to be able to control all three LEDs independently. Are the PWM signals synchronous, so just one pin needs to be monitored for changes in PWM to high?
Thanks, DW 
[code]/*
// Assign constants
const int analogInPin = A0; // Analog input pin that is attached to first light 2 voltage sensor
const int analogInPin1 = A1; // Analog input pin that is attached to second light 2 voltage sensor
int adjustment = 2;
int sensorValue = 0; // value read from sensor 0
int sensorValue1 = 0; // value read from sensor 1
int outputValue = 0; // map output 0-1023 to 5000 mV, store in outputValue
int outputValue1 = 0; // map output 0-1023 to 5000 mV, store in outputValue1
//For RGB common anode LED
const int redPin = 9; //LED lead 1, looking left to rt
const int greenPin = 10; //lead 3 left to rt
const int bluePin = 11; //lead 4 left to rt
int powerPin = 0; // current pin to be powered
int brightnessRGB = 0; // brightness level
//Keep track of time
unsigned long count = 0; // Counts the number of seconds since the sketch started
void setup() {
// Set the LED pins as outputs:
pinMode(redPin, OUTPUT);
pinMode(greenPin, OUTPUT);
pinMode(bluePin, OUTPUT);
Serial.begin(9600);
Serial.println("Enter color (R, G or B) and brightness (0 to 9). r5g0b0 for red, etc");
delay(2000);
}
void loop() {
//Control of RGB LED
if (Serial.available() >0) //Serial.available >0, or "true", if text is entered in serial monitor
{ //Watch for input text. If input present, start reading with while loop
Serial.println();
Serial.print(" *** New RGB Setting: ");
while (Serial.available() >0)
{ //while loop 1. Reads one character at a time
//Serial.available >0, or "true", until the end of the input text is reached
//Serial.available = 0, or "false", after all text is read
int RGBinByte = Serial.read(); //Copy the text in Serial.read into RGBinByte
//Now use Serial.write to echo the input.
//It prints or echos one character with each pass of the while loop.
Serial.write(RGBinByte); //Serial print r g b
// Respond to the values 'r' or 'R', etc
if (RGBinByte == 'r'||RGBinByte == 'R') {
powerPin = redPin;
}
if (RGBinByte == 'g'||RGBinByte == 'G') {
powerPin = greenPin;
}
if (RGBinByte == 'b'||RGBinByte == 'B') {
powerPin = bluePin;
}
//The LED pin has been chosen at this point, now set power level
if (RGBinByte >= '0' && RGBinByte <= '9') {
//Map the incoming byte value (0-9) to the range of the analogRead() command (0-255):
//Reverse of normal mapping because high voltage from PWM pin blocks current flow, causing low light level.
brightnessRGB = map(RGBinByte, '9', '0', 0, 255); //common anode, so high value yields low light
//print brightness
Serial.print(" ");
Serial.print(255-brightnessRGB);
Serial.print(" * ");
//Set the current pin to the current brightness:
analogWrite(powerPin, brightnessRGB); //Eg, input b9 will power blue LED to max level
} //Exit if statement
} //End of while loop 1
//If-statement flows here after all input has been read-in and echoed by while loop
} //Exit if (Serial.available) loop
// read the analog in values from the 2 sensors:
sensorValue = analogRead(analogInPin);
sensorValue1 = analogRead(analogInPin1);
Serial.print(sensorValue);
Serial.print("\t ");
Serial.print("\t sensor 1 = ");
Serial.print(sensorValue1);
Serial.print("\t ");
count++; // Increment the count of the number of seconds.
}
delay(1000);
}
[/code]