Elenco Electronics 202 - Manual (Page 20)

-19-
Project #9
OBJECTIVE: To make a circuit that detects the conduction of
electricity in different materials.
Rebuild the circuit from project #7 but leave the on-off switch out as
shown on the left.
When you place a metal paper clip across the terminals as shown in
the picture on the left, current flows from the batteries (B1) through the
resistor (R1), through the LED (D1), and back to the battery. The
paper clip completes the circuit and current flows through the LED.
Place your fingers across the terminals and the LED does not light.
Your body is too high of a resistance to allow enough current to flow to
light the LED. If the voltage, which is electrical pressure, was higher,
current could be pushed through your fingers and the LED would light.
This detector can be used to see if a material like plastic is a good
conductor or a poor conductor.
Conduction Detector
Project #10
OBJECTIVE: To combine the sounds from the space war and
alarm integrated circuits.
Build the circuit shown. Turn it on, press the press switch (S2) several
times, and wave your hand over the photoresistor (RP) to hear all the
sound combinations. You can make the sound from the alarm IC (U2)
louder by replacing the 100
Ω resistor (R1) with the 6V lamp (L2).
Space War Alarm Combo