Elenco Green Projects - Manual (Page 66)

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50mA
Project #106 Clock with Memory
Triple Current Meter
Build the circuit shown. This circuit measures
current using several scales on the meter
(M6). Set the slide switch (S5) to position C.
Place the solar cell (B7) in sunlight or near
an incandescent lamp, and vary the light on
it. Use the 0.5mA or 50mA settings on the
meter to measure the current through the red
LED (D1).
If the current is too high to measure on the
0.5mA setting and too low to measure on the
50mA setting, use 0.5mA and push the press
switch (S2); this uses a resistor in the pivot
stand to change the scale to 5mA.
Set the slide switch to position B. This places
a high resistor (in the pivot stand) in series
with the LED. Measure the current now.
Build the circuit, and set the switch (S5)
to position B to turn on the clock. If you
turn off the switch or disconnect the
power source (the B4 battery), the clock
will still work for a while. The 470
μF
capacitor (C5) stores enough electricity
to run the clock for a while during power
disruptions. If you remove the capacitor,
the clock will turn off when you turn off
the switch.
See page 4 if you would like to set the
time.
Project #105
If you don’t have a
suitable light source,
you can use the
battery (B4) in place of
the solar cell.
Many clocks use
capacitors or small
batteries as backups in
case the power goes
out for short periods.
0.5mA
See projects 1 & 3 if you need to recharge the battery (B4).