Moisture Test notes - SteveCossy/IOT GitHub Wiki

The moisture probe calibration on all system depends on soil / whatever type and composition but you might like to try this: All materials will have a different water carrying capacity so...

• Fill a clay pot with representative soil / potting mix, sand / clay etc in it
• Saturate it full immersed in water and drain for an hour
• Drain for an hour / few hours Weigh it and note 'Wet grams'
• Insert the two probes / nails and note this as the 100% reading
• Watch it dry out to a minimum point You could let it dry FULLY in hot warm place and note the dry weight If you did the wet - dry as percent = total grams water from 0 to 100% then you could work out the ratio as things went through a few mid points of dryness and took actual total grams as above you can develop a 'calibration slope' for the instrument. The EEPROM is able to hold 256 points of a non linear curve so that is better than 0.5% accuracy if needed for the super fussy :)

Immerse your now calibrated pot into the garden / forest floor / frog area etc

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I have actual Rh% (air) instruments that are as simple as the DS18B20 to use but these require most of the pins of an 08M2 to make the I2C bus work but are ready in the bits box in the shed.