Watermark Moisture Sensor

[cmartinsen]

I am trying to read a watermark sensor in conjunction with a DC opensprinkler system. I’ve found some great reference materials from the Vinduino project on hooking up a watermark sensor to Arduino (http://vanderleevineyard.com/1/post/2012/08/-the-vinduino-project-3-make-a-low-cost-soil-moisture-sensor-reader.html) but the system outlined uses 2 analog and 2 digital ports to simulate an alternating current.

I’m wondering if anyone has experience doing this with a transistor and reducing the ports to 1 analog and 1 digital port? I’d love to integrate the tried and true watermark sensor into the system, but 4 ports is a lot to use for 1 sensor.

Here is the circuit I am referencing:

Thank you for any direction or assistance,
Craig

[Ray]

I’ve done some research on soil moisture sensor in the past, which you can find in this blog post:
https://rayshobby.net/reverse-engineer-a-cheap-wireless-soil-moisture-sensor/

The chirp sensor seems to be quite reliable:
https://www.tindie.com/products/miceuz/i2c-soil-moisture-sensor/
This is a capacitive sensor (with no expose leads, so it’s more reliable) and it uses the I2C interface.

I’ve taken a quick look at the Vinduino sensor — it seems to be a resistive sensor, but it uses two digital pins to create AC to avoid corrosion. The two digital pins are used to create alternating polarity, but also to create a state where no voltage is applied on the sensor at all. To reduce the number of digital/analog pins, one thing you might be able to leverage is that the analog pins on Arduino can also be used as digital pins. So perhaps you can use two analog pins. Set one as digital and output a high, while the other is set as analog for reading signal. Not sure whether this would work or not (because the analog reading will end up affecting the net voltage applied on the sensor)

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