The simple conjuring trick in Figure 1 is intended to provide some enjoyment for the beginner in electronics or conjuring, and should take only an hour or two to build.
The trick works as follows: a wand (with a magnet mounted
in one end) must pass in a 1-2-3 sequence over reed switches S4 to S6 before
the bulb LP1 will light. If the wand passes over reed switches S1, S2,
or S3, the 1-2-3 sequence will be reset (that is, cancelled). Or, if the
bulb is already burning, the activation of reed switches S1, S2, or S3
will extinguish it.
All the reed switches – S1 to S6 – are glued just beneath
the surface of a 10 cm² box (Figure 2). A general purpose adhesive
is suggested, so that the reed switches may later be moved if necessary.
The bulb, LP1, is mounted in the centre of the box. A small PP3 9V battery
may be used. The prototype box was built using balsa wood.
The wand may be waved back and forth in various motions
over the box, on condition that it finally passes in the correct 1-2-3
sequence over S4 to S6 (at which point LP1 will light). This should thoroughly
confuse any onlooker and make it virtually impossible for another person
to repeat the correct motions with the same wand. The wand may also be
lifted just high enough over reed switches S1 to S3 so as not to trigger
A 7.2V filament bulb, LP1, was used – instead of, say, a LED – so as not to give the trick an “electronic” appearance.
The operation of the circuit is fairly simple. Three AND logic gates of a 4081 CMOS IC are employed, with gates IC1a to IC1c beingconfigured as a standard cascaded latch circuit. S1 to S3 serve as reset switches. The output at pin 10 will only switch to logic high when reed switches S4 to S6 are closed in sequence. Power transistor TR1 amplifies
the output current to light bulb LP1.
Instead of a wand, a small neobdymium (super-strength)
magnet may be stuck to one finger, and one’s finger used in place of the
In “stand-by” mode (with the bulb extinguished) the circuit
will use very little current. Therefore a switch is not included in the
circuit (of course, one may be added). The box may be opened and the battery
simply clipped on or off.