I am looking to make a capacitive soil moisture sensor; having looked at all possible kinds of detectors I found that this soil moisture detector should meet the following requirements:
1. hardware based (not involving any controller programming)
2. not based on measuring resistivity or using currents: even with AC and stainless steel probes this leads to corrosion over time
3. RF based using capacitive probes (no use of current, see 2)
4. frequency range 100MHz +/- 50MHz (to avoid influence of soil minerals)
5. output voltage within 0 to 5V range, but not required to extend to this full range
6. sensor probes must be able to be self-made, ie. PCB board (see attached files)
Some research dug up the following coverage:
https://www.edaboard.com/showthread.php?t=353365 (the relevant thread is closed and the original author cannot be found)
Using an AD8307 RF logarithmic amplifier and a LTC6905 100MHz oscillator.
Questions:
1. I have a hard time locating for purchase this LTC6905 oscillator. Is there an equivalent way to produce, with a single IC, a 100MHz square wave signal 50% duty cycle with an output driving a 600 ohm load, rail-to-rail?
2. In attachment you find some design considerations, copied from the original thread: would you please have a look at those and let me know your comments re. feasibility, corrections,..?
Thank you!
Erik