Data Sheet

-32-

30. Light Emitting Diode

Build the circuit shown on the left. Turn ON the switch (62) and the heart

LED (69) will light. LED stands for Light Emitting Diode. The Diode is the

component that only allows the current to ow in one direction, but an

LED is a special type of diode that emits light whenever the current does

ow in the designed direction.

31. Detecting Fluid Levels

Replace the switch (62) with the reed switch (83). Move the magnet (7)

near the reed switch (83) and the heart LED (69) will light. Move the

magnet (7) away from the reed switch (83) and the heart LED (69) will

go off. Reed switch circuits like this can be used to detect uid levels for

coffee makers, dish washers, washing machines and water heaters. By

putting a magnet on a oat, which rises and falls with the liquid in the

container, the magnet can trigger a reed switch circuit that turns on a

warning light whenever the liquid, and by extension, the magnet, reach

a certain level.

32. Ship to Ship Morse Code

Replace the reed switch (83) with the press switch (61). Press the press

switch and the heart LED (69) will ash ON and OFF. This can be used as a

Morse code typing simulator. Morse code uses various sequences of long

and short on-off tones, lights or clicks to represent letters, numbers and

text. Since World War II, the process for sending messages using signal

lamps has barely changed. It requires someone trained in Morse code to

operate the lamp’s shutter by hand, receiving, decoding, and replying to

messages.

33. Conductivity Tester

Build the circuit shown on the left. Try connecting various objects across

points A and B (they will have to be small objects that can touch the pins at

points A and B like a paper clip). If the object is a very good conductor, then

it will enable all the current to ow through it, bypassing the heart LED (69)

and the heart LED (69) will turn off. If the object is a very poor conductor,

then very little current will ow through it while most of the current will ow

through the heart LED (69) making it light.