FUNDAMENTALS FOR THE BEGINNER
Build a Moisture Detector
A kit for these experiments can be purchased
from the Nuts & Volts Webstore at
www.nutsvolts.com or call us at 800-783-4624.
If you’d like to test plant soil for moisture, you can use this circuit to do so. The more moisture there
is, the faster the LED will blink.
Build the Circuit. Using the schematic along with the pictorial
diagram, place the components on a solderless breadboard as
shown. Verify that your wiring is correct.
Do the Experiment. Theory: We are using the 555 timer IC as a
clock with the frequency controlled by the amount of resistance
between the probes. The lower the resistance, the more blinks per
second. By experimenting with different soils, you will get used to
reading the results. With practice, you will be able to tell the
approximate amount of moisture by observing the blinking LED.
Procedure: Connect a
nine volt battery to the
battery snap and
observe that the red LED
may or may not be on. If
you touch the probe
wires together or put
them into water, the LED
will blink. The more
moisture, the faster the
blinking.
SCHEMATIC
PICTORIAL DIAGRAM
These experiments
are provided by
GSSTechEd at www.gssteched.com
Resistors, 1/2 watt 5%
GK01049 220 ohms (R3)
GK01065 1,000 ohms (R2)
GK01085 6,800 ohms (R1)
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February 2012
WIRES
W1 = 7b and 30b
W2 = 19a and 30c
W3 = 19h and 30h
W4 = 12j and 30j
W5 = 16g and 19d
W6 = 17d and 18g
W7 = 16d and 12c
PROBE WIRES
Probe #1 in hole 27c
Probe #2 in hole 17a
