■ FIGURE 2.
two transistors (Q1 and Q2). They look similar, but
Q1 is a PNP and Q2 is an NPN, so they are not
interchangeable. Be sure each transistor gets mounted
in the proper location and orientation (refer again to
Before installing capacitors C1 and C2, take a look
at Figure 3. Both capacitors C1 and C2 have to be
mounted on their sides — against the circuit board — to
provide clearance for the enclosure’s plastic cover. Bend
both wires as shown before soldering each capacitor. An
aluminum spacer is mounted on the PCB in order to
position the coil directly below the pendulum. Make
sure that the spacer is on the component side and the
■ FIGURE 4.
■ FIGURE 3.
screw is inserted on the bottom side of the
board. Now, place the coil over the spacer and
solder the two wires as shown in Figure 2.
Next, install the T1 LED on the PCB. If you
look carefully at the LED, you will see that one
leg is shorter than the other; the LED may have a
flat edge near one of the legs. The flat spot or
short leg indicates the cathode leg. The LED should be
mounted at a height of 3/4” from the PCB. This height
will allow the LED to protrude through the hole in the
enclosure’s cover during final assembly. Lastly, attach
two 10” wires to the PCB as shown in Figure 2. The
other ends of these wires will attach to the solar cell
Now, move on to the enclosure that will become
the pendulum’s base, and will house the circuit board
and coil. Carefully drill the four holes in the lid, at the
locations shown in Figure 4. The solar cell should be
mounted at the top of the threaded rods to collect as
much light as possible. Cut a small piece of plastic
1” x 3” to hold the solar cell, and drill two holes
for the rods.
Then, assemble the threaded rods, hex nuts,
circuit board, and solar cell holder to the
enclosure’s lid as shown in Figure 5. Be sure to
use stainless steel rods and nuts, so the metal
parts will not interfere with the magnetic field.
Choose some thread and a small object for the
pendulum. Use the thread to suspend the
pendulum object from the plastic piece at the top
of the rods as shown in Figure 5.
The solar cell for this project should output at
least 4.0V 20 mA. On the bottom side of the
solar cell, you will see two pads for soldering near
the corners. Be sure to note the polarity marks for
“+” and “-” next to each pad. The power wire that
goes to +V on the PCB gets soldered to the + pad
on the solar cell. Likewise, the power wire from
GND on the PCB gets soldered to the - pad. Try
not to apply excessive heat when soldering the
wires to the solar cell to avoid damaging it.
Refer again to the final assembly diagram
(Figure 5). The black plastic enclosure (shown in