Hi all, I am new to using Arduino and am having a few issues on a project I am working on. Essentially I need to monitor soil moisture contents at a fairly high degree of accuracy.
At the moment I have an Arduino UNO and a Vegetronix VH400 soil moisture probe (http://www.vegetronix.com/Products/VG400/).
I have been doing some tests to get my calibration curve as accurate as possible. Starting with dry soil, adding a few mL every half an hour and monitoring the values Arduino give me. I have gone thorough this process about 10 times, and have plotted all of the data points. In dry soil I get a value of around 175, and in saturated soil I get a value of about 630. When I put the sensor into a glass of water the value is also around 630.
It looks like the relationship between voltage and soil moisture content is approximately linear, however there is some variation. For example, with a soil/water mixture of 50%, I have received values ranging from 360 to 400. The range in results is similar if I use 5v or the 3.3 volts.
I am trying to find a way of using as much of the 0 - 1023 as possible (i.e.: achieving a value closer to 1023 when putting the sensor into water). I think this may allow me to obtain a more accurate calibration curve. Someone has mentioned that using a signal amplifier may help, I have done some reading but am still not sure if it going to help with what I need.
If anyone has any suggestions it would be very appreciated.