Watermark 200SS-interface

[Ton_vN]

In meteo-applications the well-known soil-moisture-sensors of type 200SS from Watermark/Irrometer usually connected to a Davis PWS.
However, that configuration not 'mandatory' and plenty of alternative devices applying those sensors.
One other interface is from SMX, with output as either Voltage, Frequency or Current, each proportional to measured soil-moisture.

'What-if' question for application of that SMX-interface:
is an ESP8266 with ESPEasy on a standard pin able to track the frequency-output ranging between 50Hz and 7kHz (for normal operation Dry~Wet) till max. 13kHz (at schortcircuit)?
Related: would measurement of that Frequency-signal be better quality than measurement of the analogue Voltage-signal by means of the internal ADC (0 ~1VDC, and max. 1,7)?

[TD-er]

Measuring an analog value will be way more stable on an ESP.
Especially on ESP8266.

On ESP32 it might be that frequency counting is a lot more stable compared to ESP8266, but still it highly depends on how regular the counting registers are being read.

And please don't use ESP8266 for new projects.
It is way more limited in any sense.

For example measuring analog values can have intereference from WiFi activity.
On ESP32-variants this is much less of an issue (when using pins connected to ADC1)

[TD-er]

Also keep in mind that the ADC on both ESP8266 as well as ESP32 (classic) is quite unusable close to 0V.

[Ton_vN]

Fortunately the SMX-doc tells that normal operational DC-output is 0.2V ~1.0V, rising to 1.7V at short-circuit.
Is within the voltage-inputrange of the ESP8266's ADC, and should be sufficiently distant from the 0V-'bottom'.
10 Bit ADC => 1024 units/full scale (of 3.3V) => SMX-readout = nominally from 64 units till 320 units, jumping to 547 units at short circuit
=> Operational range of 256 units is not high resolution, but keep in mind what we are measuring ..........

Absolute scaling might be slightly widened by application of the current-interface for the SMX-device, but that is only 'cosmetic' improvement of resolution.

[Ath]

If you need a better resolution, you could use an ADS1115/ADS1015 (P025), INA219 (P027) or INA3221 (P027) voltage converter, as these offer range configuration and a higher resolution A/D converter.

Edit: Using an INA converter, you could also use the Current output configuration of the sensor, but the resolution might be reduced by that, didn't do any math on it

[Ton_vN]

@Ath

Yes, better resolution from the ADC if using an ADS1115 in combination with some fidlling with it's setup.
But it does not effectively improve the bandwidth of the signal you get from the sensorcell .....
Same if you use the 'current'-setup.
The technical aspects of signalmeasurement can reasonably be solved, but it is not the whole story.
[IMHO] the hidden functional pitfall for application of these sensorcells is that you have to calibrate for your local soiltemperature [versus the Californian calibration soiltemperature of 24C] and related to your local type of soil.
The 1st aspect is rather easy, because Irrometer provides the calibration curves and the formulae.
The 2nd aspect requires knowledge & skill how to identify type of soil and refer it to the provided triangular diagram,
and it raises the question where on your plot the measurement is 'representative' for the whole plot.
That is a completely different, limiting twist to functional application,
not invented by me, because you can read this in the documents from Irrometer and SMX .......