Soil Moisture Indicator
Model GSK-908
This circuit utilizes four LED’s to indicate the level of moisture
in the soil. An increase in the number of LED’s on indicates
an increase in the amount of moister present.
Technical Specifications
n Power source: 9 V DC
n Power consumption: 20 mA max.
n Moister measurement: 4 levels
n PCB dimensions: 1.59 x 0.84 inches
Operating Principles
Current through resistor 1 to the moister in the soil and
received at transistor 1 when probes “P” and “I” are inserted
into the soil. Emitter and collector current of transistor 1
display results through a series of 4 LED’s. The greater the
moisture at “I” the more voltage will pass through transistor 1
and more LED’s will be lit. If there is low moister little or no
current will pass through transistor 1 and few or none of the
LED’s will be on.
Figure 1 Installing components
PCB Assembly
Please refer to Figures 1, 2, and 3 for aid in component
placement. It is recommended to start with lower components
i.e. diodes, resisters, capacitors, and transistors. Be careful to
check polarity with Figure 3 before soldering. If a problem is
detected it is best to use a desoldering pump or desoldering
braids to remove component. This will minimize potential
damage to the printed circuit board.
Testing
Make to probes out of hard wire and connect at “P.”
Connect 9 V DC battery and submerge probes into water,
all LED’s should turn on.
Troubleshooting
The main cause of problems will come from misplaced
components or faulty soldering. Utilize Figures 1, 2 and 3
to ensure proper placement, polarity and then check solder
points for connectivity.
Accessories
Use GSB-01 (sold separately) to house the PCB and batteries.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
Electronic Kit Set for Hobby & Education
TestEquipmentDepot.com
Figure 2 Soil moisture indicator circuit
Figure 3 Connecting Circuits
GSK-908
Resisters Transistors
R1, R4 1 kΩ brown-black-red-gold
R2 120 kΩ brown-red-yellow-gold
R3 2 kΩ red-black-red-gold
R5 680 Ω blue-gray-brown-gold
R6 470 Ω yellow-violet-brown-gold
TRI = C458, C828, C945, C1815
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