Elenco Upgrade Kit SC100 to SC500 - Manual (Page 35)

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Project #197
OBJECTIVE: To sound an alarm when water is
detected, tone will vary with salt content.
Build the circuit at left and connect the two (2) jumpers
to it, place the loose ends of the jumpers into an empty
cup (without them touching each other). Press the
press switch (S2) - nothing happens. Add some water
to the cup and an alarm will sound. Add salt to the water
and the tone changes.
You can also test different liquids and see what tone
they produce.
Water Alarm
Project #198
OBJECTIVE: To hear your voice on the radio.
You need an AM radio for this project. Build the circuit shown but do
not turn on the slide switch (S1). Place it within a foot of your AM radio
and tune the radio frequency to the middle of the AM band (around
1000 kHz), where no other station is transmitting. Turn the volume up
so you can hear the static. Set the adjustable resistor (RV) control to
the middle setting. Turn on the slide switch and slowly tune the
adjustable capacitor (CV) until the static on the radio becomes quiet.
You may hear a whistle as you approach the proper tuning. In some
cases you may also need to set the adjustable resistor slightly off-
center.
When the radio static is gone, tap on the speaker (SP) with your finger
and you should hear the sound of tapping on the radio. Now talk loudly
into the speaker (used here as a microphone) and you will hear your
voice on the radio. Set the adjustable resistor for best sound quality at
the radio.
Radio Announcer