Elenco Green Projects - Manual (Page 67)

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Project #108 Stopped Motor Alarm
Capacitor Charging
Build the circuit shown. Set the meter to the
0.5mA setting. Set the slide switch (S5) to
position B, place the solar cell (B7) in
sunlight or near an incandescent lamp, and
push the press switch (S2). The solar cell
slowly charges up the 470
μF capacitor (C5),
and the meter shows the current.
Set the slide switch to position C to discharge
the capacitor, making the red LED (D1) flash.
Set S5 back to B, push S2 to see the current,
and then set S5 back to C to see the flash.
Build the circuit shown and press the
switch (S2) to spin the fan on the motor
(M4). The horn (W1) sounds briefly until
the fan gets going.
Stop the fan with your finger. The horn
sounds an alarm to let you know that the
fan is not spinning.
Project #107
If you don’t have a
suitable light source,
you can use the
battery (B4) in place of
the solar cell.
Warning systems like
this are often used to
alert us when
something is wrong with
a mechanical system.
0.5mA
See projects 1 & 3 if you need to recharge the battery (B4).