using a cheap simple transformer as the power source
Vout (4.7V approx.) goes to pin 2.Pin 2 goes to Arduino GRD with 10k Ohm in series (pull down)
If you just have a transformer then the power source is AC. Are you sure it's just a transformer or is it a DC power supply?
Is the sensor responding to 50/60Hz lighting the room?
If you are reading from the voltage divider you don't need a pull down resistor, and in fact it is parallel with your lower divider (the 6k9) resistor so will lower the voltage level considerably. Did you measure 4v7 with that pulldown in place?
You do have ALL grounds tied together?
Quote from: Graynomad on Sep 29, 2012, 12:54 amIf you just have a transformer then the power source is AC. Are you sure it's just a transformer or is it a DC power supply?I think (and very much hope) that it gives DC because it was 'borrowed' from an expensive spectrophotmeter. That said, It is a generic replacement for a supply that went west. I checked it before using it for this project and saw precious little information written on it - but increduality (and knowing that it succesfully charges the spectro's battery) led me to dismiss any worry.