Data Sheet

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54. Polarity Tester
Build the circuit shown on the left. If you connect the 4.5V terminal
of the battery (91) to point A and the “–” terminal of the battery (91)
to point B, you will see the heart LED (69) light. If you connect the “–”
terminal of the battery (91) to point A and the 4.5V terminal of the
battery (91) to point B (use the spring wire (9) to help you do this), then
the star LED (70) will light. This circuit acts as a tester to see which
side of a battery is the positive side and which is the negative side.
55. Help!
Build the circuit shown on the left, press and release the press switch
(61) and you will see the heart LED (69) ash on and off. This circuit
can be used for practicing telegraph typing. Try using this circuit as a
Morse code generator (see project #36) and tap in the code below. This
stands for S.O.S, or Save Our Souls. If you ever see this pattern then it
means someone is in danger and calling for help.
S O S
lll – – – lll
+
–