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Humidity detector
YOU WILL NEED
+ 2 resistors, 470 Ω
+ 1 resistor, 3.3 kΩ
+ 1 resistor, 22 kΩ
+ 1 resistor, 100 kΩ
+ 1 resistor, 220 kΩ
+ 3 short wire bridges
+ 2 long wire
connectors
+ 2 LEDs
+ 2 transistor modules
+ electronics board
+ battery clip
+ and additional household
items: 9-volt square battery,
glass of water
HERE'S HOW
1. Assemble the circuit following the
circuit diagram. You will use the
loose ends of the two long wires
("A" and "B") as "sensors."
2. Fill a glass with tap water.
3. Dangle the two long wires A and B
into the glass.
What happens?
4. Now pull the
wires back out of
the glass.
5. Hang the two
wires in the water
again and wait a
couple days.
What happens
when the water
evaporates?
A
R1
220 KΩ
B
R2
100 KΩ
A
R 1
B
220 k
Conductance
EXPERIMENT 1
R6
LED2
470 Ω
LED1
R3
470 Ω
A
A
C
T1
LED 1
R 3
470
R 4
22 k
T1
R 5
3.3 k
R 2
100 k
17
+
C
–
T2
R4
22 KΩ
R5
3.3 KΩ
LED 2
R 6
470
+
9V
–
T2
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