(Re) Testing the variable frequency oscillator

(Re) Testing the variable frequency oscillator

Soil Moisture Sensor

After designing an oscillator, it was time to see whether it would respond to changes in moisture. It is winter at the time of this test which means that it will take a while for water to evaporate. This means we need something that will evaporate a bit faster than water.

Luckily I have a supply of awful, cheap gin on hand that can be used for this test.

So here is the setup for the first test. At the top of the photo is the antenna and radio receiver. From left to right in the bottom of the photo is the power supply resting on a plastic sleeve, the oscillator built on bread board with the sensor covered in a little bit of paper towel on top of it.

The beaker is not full of gin. I was going to use water but I changed my mind.

So how does the test work?

Gin soaks the paper towel that is sitting on top of the sensor. This increases the capacitance of the sensor, which decreases the frequency of the oscillator. The radio receiver scans a whole range of frequencies and detects the fact that the frequency of a strong signal (it is strong because it is near the receiver) has changed.

I ask the radio receiver to check which frequency has a strong signal once per minute for four hours. After four hours, the computer shows me where the strong frequency and how it changed with time.

As the gin evaporates, the capacitance of the sensor will decrease which means that the frequency will increase over time.

After four hours of waiting, the computer showed me that the strong frequency was…

…somewhere in there. I have no idea what is going on in that picture.

There should be one line that starts in the top left of the picture and then moves to the right as you head down the picture. This looks like bad 80’s CGI.

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