This is much better than the previous resistance soil moisture sensor.
The previous type of resistance sensor because the exposed copper lead it is particularly susceptible to corrosion.It will be broken for a few months.But the new one Analog Capacitive Soil Moisture Sensor It is made of a corrosion resistant materal giving it a long service life.Three months ago, I bought it, and continued to work for three months without a bit of trouble.
If you are looking for a soil moisture sensor will not rust, hope this can help you.
Interesting looks like a TLC555 (SOIC is marked TL555C) is using the soil moisture probe as its timing capacitor. As the soil gets wet the capacitance goes up. Does it output a pulse or is the output filtered into an analog value.
ron_sutherland:
Interesting looks like a TLC555 (SOIC is marked TL555C) is using the soil moisture probe as its timing capacitor. As the soil gets wet the capacitance goes up. Does it output a pulse or is the output filtered into an analog value.
I see the schematic now, it was on the wiki page, thanks.
Something looks wrong, the Frequency to Voltage converter looks more like a peak detector. Anyway, I did a simulation of the circuit to see what the analog voltage would look like if the sensor part was put in a swimming pool (e.g. a switch adds 100pf which is likely more capacitance than the sensor would get from the swimming pool). A push button is used to get the peak detector near a stable output voltage before closing the switch that simulates a swimming pool.
The timer changes frequency from 800kHz to nearly 700kHz, which does change the peak detector output some. The output may change just enough to be measurable with a 10 bit ADC. With that said I'm not very impressed with the F/V method used. I have been running these CMOS 555's at less than 10kHz and sending the pulse to an ICP pin, but this circuit runs too fast for ICP. It may work with the T1 input pin, which could count pulses for a mSec or so. That would give a much better idea of the moisture level compared to a few mV on an ADC.
Vinduino looks like an interesting project. Some of the images are not showing (at the moment). There seem to be several of these projects going on. My project started simple, but then I wanted better data gathering...
I tend to obsess with getting the electronics right. I'm not sure what to think of the Gypsum sensor, I don't really understand what is causing its resistance to being fundamentally related to the soil moisture (what if the roots release organic acids). I think that is import to keep things simple. Capacitive moisture sensing is very simple, once the idea of relative permittivity is grasped. There are no chemical reactions, so it should be possible to make a sensor that lasts for a very long time.
