In the course of one of our Makership Projects, we needed a water turbidity sensor. Of course a new sensor was prohibitively expensive, but eBay pointed us towards inexpensive dishwasher sensors. We ended up purchasing a Whirlpool Turbidity Sensor, part number 99002650
Pin 1 -> Thermistor
Pin 2 -> Turbidity (photoresistor)
Pin 3 -> Photodiode
Pin 4 -> +5V Power Supply
To use this sensor with an Arduino:
Tie pin 1 to an analog input, and connect that pin via a 10K pull down (to ground) resistor
Tie pin 2 to an analog input, and connect that pin via a 3K pull down (to ground) resistor
Tie pin 3 to ground with a 150ohm resistor
Tie pin 4 directly to 5V power
We weren’t able to find much pinout information online so we thought we’d document this somewhere in the hopes of helping someone else.