Hello,
I am also experimenting with Arduino turbididty sensor. I am using Arduino Duemilanove with 2x16 LCD screen. The LCD module, that clips straight to Arduino has analog outputs brought out along with GND and 5V pins. If I set the turbididty meter to Analog and connect all wires to turbidity meter, I get voltage readings:
- in completely dark room and nothing between the sensor = 3.84 V
This should be 0 NTU (the datasheet says it is measuring from 0 NTU to 3000 NTU). - in dark room, with untransparent paper between the sensor = 0 V
This should be 3000 NTUs.
So I made a linear function of this where in graph x1, x2, y1,y2 are known.
Basic linear function formula: y = m*x + b
Where m is the slope of the line, calculated m = (y2-y1)/(x2-x1)
b is intercept with y-coordnate, where x = 0.
So got the voltage to NTU conversion formula:
ntu = (-781.25*volt) + 3000
volt is measured by Arduino.
Seems to work.
Measurements should be done also in completely dark environment, like some small plastic bottle (ex old plastic film can). If I shine some extra light to the sensor the voltage goes higher. Although I do not know, if the analog output voltage is linear or logaritmic. At the moment I am assuming linear.
Also to be noted, that scientific turbidity meters are measuring in an angle, and the reflectance/scattering from the particles in fluid. But this sensor straight light intensity from the light source to detector. So cannot compare with scientific devices, because these two are completely different and have different accuracy.
