Elenco Electronics 202 - Manual (Page 58)

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Project #111
OBJECTIVE: To transmit Space War sounds to a AM radio.
Place the circuit next to an AM radio. Tune the radio so no stations are
heard and turn on the slide switch (S1). You should hear the space war
sounds on the radio. The red LED (D1) should also be lit. Adjust the
variable capacitor (CV) for the loudest signal.
You have just performed the experiment that took Guglielmo Marconi
(who invented the radio) a lifetime to invent. The technology of radio
transmission has expanded to the point that we take it for granted.
There was a time, however, when news was only spread by word of
mouth.
Space War Radio
Project #112
OBJECTIVE: To show how sweat makes a better conductor.
The Lie Detector
Turn on the slide switch (S1) and place your finger across points A &
B. The speaker (SP) will output a tone and the LED (D2) will flash at
the same frequency. Your finger acts as a conductor connecting points
A & B. When a person is lying, one thing the body starts to do is
sweat. The sweat makes the finger a better conductor by reducing its
resistance.
As the resistance drops, the frequency of the tone increases. Lightly
wet your finger and place it across the two points again. Both the
output tone and LED flashing frequency increase, and the lamp (L2)
may begin to light. If your finger is wet enough, then the lamp will be
bright and the sound stops - indicating you are a big liar! Now change
the wetness of your finger by drying it and see how it affects the circuit.
This is the same principle used in lie detectors that are sold
commercially.