23
Build the circuit shown. Set the meter (
M6
) to the
0.5mA
setting. The clock display will light, but the meter
will not measure any current. See page 4 if you would like to set the time.
The clock needs only about 0.005mA of current to operate, and this is too small to measure on your meter.
The battery can run the clock for a long time without being recharged.
Build the circuit shown. Set the meter (
M6
) to the
0.5mA
setting. Flip the switcher
(
S6
) back and forth between its left and right positions to charge and discharge
the 470
μ
F capacitor (
C5
).
With the switcher set to the right, a electricity briefly flows from the battery into the
capacitor to charge it up, as shown by the meter. With the switcher set to the left,
the energy in the capacitor discharges through the red LED (
D10
), which flashes.
The meter only measures current in one direction, but you can flip it around to
measure the discharge current.
PROJECT 22
• Clock
PROJECT 23
• Capacitor
The clock uses a liquid display (LCD) to show the
time. LCDs use very little power, but cannot be viewed
in darkness. The electronic circuitry that keeps time,
controls the display and allows you to set the current time
is complex but has been miniaturized in an integrated
circuit (IC).
Capacitors store electricity in an electric field between
metal plates, with a small separation between them. This
electric field is similar to the magnetic field of a magnet.
Compared to batteries (which store energy as separated
chemicals), capacitors can only store small amounts of
energy, but they can release it quickly, can be made in
very small sizes and are inexpensive.
0.5mA
0.5mA
See project 3 if you need to recharge the battery (
B4
).