Mini Liquid Level Sensor

The Mini Liquid Level Sensor is similar to the moisture probe in that it applies voltage and detects current through the liquid.  As with soil, the current flow is made possible thanks to minerals in the water, which make it possible to for electrons to move between probes (electric current).  The sensor converts this current to voltage that can be measured by the micro:bit.  As the level increases, so does the voltage.  Tap water is recommended because distilled or fully purified (deionized) water does not contain the minerals needed to conduct electricity.

Parts

(1) Mini Liquid Level Sensor (28090) 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

Liquid level can be below the sensor (0 V).  As it covers more of the plated lines, the voltage measurement will increase.  Monitor the micro:bit module’s 5×5 LED voltage display as you add water.  IMPORTANT: Do not allow the water level to go above the plated lines.