Moisture Sensor

I'm trying to do a soil moisture sensor, follow this example:

http://orionmultitouch.blogspot.com/2010/02/arduino-simple-moisture-tester.html

I am using a 10K ohm resistor, But my results were different when I connect the two ends directly, the value received in 1023, according to my calculations and it shows in the video, is correct:

1023 the two ends connected directly and 0 when the two are disconnected ...

sensor = 1023 sensor = 1023 sensor = 1023 sensor = 1023 sensor = 0 sensor = 0 sensor = 1023 sensor = 1023 sensor = 1023 sensor = 1023 sensor = 1023

I took a glass with water and put the two ends in the cup, my result was this:

sensor = 351 sensor = 322 sensor = 321 sensor = 312 sensor = 308 sensor = 306 sensor = 300 sensor = 295 sensor = 291 sensor = 286 sensor = 282 sensor = 278 sensor = 274 sensor = 274 sensor = 273 sensor = 272 sensor = 271 sensor = 272 sensor = 271 sensor = 272 sensor = 272 sensor = 271 sensor = 272 sensor = 271 sensor = 271 sensor = 271 sensor = 271 sensor = 274 sensor = 272 sensor = 272 sensor = 272 sensor = 271 sensor = 272 sensor = 272 sensor = 272 sensor = 272 sensor = 271 sensor = 271 sensor = 272 sensor = 271 sensor = 272 sensor = 271 sensor = 271 sensor = 272 sensor = 273 sensor = 272 sensor = 272 sensor = 272 sensor = 272 sensor = 273 sensor = 273 sensor = 273 sensor = 273 sensor = 273 sensor = 273 sensor = 274 sensor = 273 sensor = 274 sensor = 273 sensor = 273

Intriguing is that the values ??fall slowly and then lie between 270 ~ 275, and in the video tutorial and the values ??are 600 ~ 650 on the ground moist, and this directly into my glass of water, What am I doing wrong?

I tried this also: http://seeedstudio.com/wiki/Grove_-_Moisture_Sensor I Made the 2N2222 transistor (2N2222A without being as it is in the schematic), but also of low and unstable (start high and slowly falling vain).

I found this other: http://www.botanicalls.com/archived_kits/twitter/

reminder: I'm using copper wire at the tip

Thanks

Water conducts based in the impurities in it so I would expect the numbers to vary greatly depending on your source of water.

I don't think you are doing anything "wrong".

Ultrapure water is hardly conductive at all while seawater approaches the conductivity of stainless steel (which really all that conductive compared to say silver wire.)

pwillard:
Water conducts based in the impurities in it so I would expect the numbers to vary greatly depending on your source of water.

I don’t think you are doing anything “wrong”.

Ultrapure water is hardly conductive at all while seawater approaches the conductivity of stainless steel (which really all that conductive compared to say silver wire.)

Interestingly,

so how could I create a rule percentage, regardless of the soil,
able to tell if it’s humid 80%, for example?

able to tell if it's humid 80%, for example?

Commercial sensor - http://www.vegetronix.com/Products/VG400/-

Think you have to do measurements with a reference (calibrated) device...