■ FIGURE 1.
the swing would eventually slow to a stop.
As long as the solar cell can keep recharging
capacitor C1 (even if it is only a partial charge), the
pendulum will trigger this invisible nudge on each swing
past the coil.
As you look through the Parts List, you will see that
this project uses fairly common parts and materials, but
it does involve some fabrication. You can view a short
video of the finished pendulum in action at
Motion From Magnets
Ampere's Law tells us that when a current is
passed through a wire, an invisible magnetic field is
produced around it. When the wire is wrapped into a
circular coil, those lines of magnetic force work
together to increase the strength of the field. The
strength of the field in a coil is proportional to the
current flowing in the wire, and the number of turns
ITEM DESCRIPTION SOURCE
R1, R2 100K, 1/4W Resistor
D1 1N914 or 1N4148 Diode Jameco (179207)
Q1 2N4403 PNP Transistor Digi-Key (2N4403-ND)
Q2 2N4401 NPN Transistor Digi-Key (2N4401TFCT-
LED1 T1 size, LED Digi-Key (754-1218-ND)
C1 2,200 µF, 10V Electrolytic Capacitor Jameco (606563)
C2 1,000 µF, 16V Electrolytic Capacitor Jameco (30015)
Solar Cell 4V 20 mA Futurlec (SZGD4026)
Base Keystone 705 Phenolic Enclosure Digi-Key (705K-ND)
Lid for Base Keystone 705 Cover Digi-Key (2042K-ND)
Magnet, coil, printed circuit board, #4-40 screws and nuts,
Aluminum hex spacer, #8-32 threaded rods and nuts
Digi-Key Corp. www.digikey.com
Jameco Electronics www.jameco.com
Tap Plastics www.tapplastics.com
Files to create your own PCB are available at the article link. The coil for
this project is rated at 6 VDC/32 ohms and can be constructed by winding
150 feet of #33 magnet wire on a plastic round core bobbin (available from
Cosmo Corporation; www.cosmocorp.com; part #7226-0).
The following items can be purchased online from:
PO Box 501
Vacaville, CA 95696
SOLPEND-KIT The complete kit of all parts for $39 plus $8 shipping.
SOLPEND-PCB Just the printed circuit board for this project for $10 plus
SOLPEND-COIL Just the coil for this project for $8 plus $4 shipping.
August 2012 33