Manual

-144-
T
his circuit works as a rain detector. This circuit
stays off and draws no current if the resistance
b
etween the long wires is more than about 250kW,
whether the key is open or closed. The speaker
produces a tone when the key is closed and water
(or anything else that has a resistance of less than
about 250kW) is connected to both of the test wires.
Connect the wires to other wires or metallic plates
laid out on an insulated surface. The alarm turns on
when water completes the circuit by spanning the
two wires or plates.
This oscillator is the basic pulse-type that we’ve
used several times in this experiment kit. The 22kW
resistor protects the circuit against excess base
current, in case the wires are shorted together. The
100kW resistor keeps any transistor leakage current
from turning on the oscillator.
N
otes:
EXPERIMENT #122: AUDIO RAIN DETECTOR
Schematic
Wiring Sequence:
o 1-29
o 2-30
o 3-104-110
o 124-4-WIRE
o 5-41-109
o 86-89-103-40
o 42-90-138
o 85-WIRE
o 119-137
o 121-122
EP-130_62315RevC.qxp_EP-130_062812 6/23/15 11:18 AM Page 144