Elenco Electronics EP-130 - Audio Rain Detector

-
144
-
This circuit works as a rain detector. This circuit stays
off and draws no current if the resistance between th
e
lon
g
wires is more than about 250k
Ω
,
whether th
e
key is open or closed. The speaker produces a ton
e
when the key is closed and water (or anythin
g
els
e
that has a resistance of less than about 250
k
Ω
) i
s
connected to both of the test wires.
Connect the wires to other wires or metallic
p
late
s
laid out on an insulated sur
f
ace. The alarm turns o
n
when water completes the circuit by spanning the two
w
i
res or
pl
ates.
This oscillator is the basic pulse-type that we’ve used
several times in this experiment kit. The 22k
Ω
k
k
r
es
i
sto
r
protects the circuit a
g
ainst excess base current, in
c
ase the wires are shorted together. The 100
k
Ω
resistor keeps any transistor leakage current
f
rom
turn
i
n
g
on t
h
e osc
ill
ator.
No
t
es
:
EXPERIMENT #122: A
U
DI
O
RAIN DETE
C
T
O
R
Schematic
Wiring
S
equence:

1
-2
9

2
-
30

3
-
104
-
110

1
24-4-
WIRE

5
-41-1
09

86
-
89
-1
03
-4
0

42
-
90
-
138

85
-WIRE

1
1
9
-1
3
7

1
21-122