Moisture Sensor Probe

Moisture Sensor Probe 

The moisture sensor applies voltage to the two plated electrodes.  In more moist soil, the plated electrodes conduct more electric current.  In less moist soil, the electrodes conduct less electric current.  The transistor circuit in the sensor represents the higher and lower currents with higher and lower voltages, transmitted by the AOUT (analog out) pin.

Parts

(1) Moisture Sensor Probe 28092 includes probe and harness
(1) Resistor 220 Ω (red-red-brown-gold)
Jumper wires: Red, black

Schematic

Wiring

Connect the harness to the probe with:

• Red to VCC
• Black to GND
• Yellow to AOUT

Then, connect red wire to 3.3 V, the black wire to GND and the yellow wire to P2 through a 220 Ω resistor

Script

Tests

Insert the probe into soil so that it covers the plated metal prongs.  Then, monitor micro:bit module’s 5×5 LED voltage display as you add water, then let it disperse and then evaporate over time.  The higher the voltage, the higher the moisture content.