Build a Magnetic Circuit: The 1-2-3 Wand Trick

The intriguing demonstration depicted in Figure 1 is intended to offer some amusement for the novice in electronics or illusion, and should require only approximately one to two hours to assemble.

Circuit Diagram

The demonstration functions as follows: a pointer (featuring a magnetic element mounted at its end) must traverse the switches S4 to S6 in a 1-2-3 order for the lamp LP1 to illuminate. If the pointer moves over the switches S1, S2, or S3, the 1-2-3 sequence will be reset (that is, cancelled). Alternatively, if the lamp is already active, the activation of switches S1, S2, or S3 will extinguish it.

All the reed switches – S1 through S6 – are affixed just beneath the surface of a 10 cm² box (Figure 2). A general-purpose adhesive is suggested, ensuring the reed switches can be repositioned if necessary later. The lamp, LP1, is situated in the center of the box. A PP3 9V battery may be utilized. The initial prototype box was constructed using balsa wood.

The pointer can be moved back and forth utilizing various motions over the box, provided it eventually passes in the correct 1-2-3 sequence over S4 to S6 (at which point LP1 will light). This should thoroughly perplex any observer and render it nearly impossible for another individual to replicate the precise movements with the same pointer. The pointer may also be raised just high enough over switches S1 to S3 so as not to trigger them.

A 7.2V filament lamp, LP1, was employed – instead of, for example, an LED – so as not to give the trick a “digital” appearance.

The operation of the circuit is relatively uncomplicated. Three AND logic gates based on a 4081 CMOS integrated circuit are utilized, with gates IC1a through IC1c configured as a standard cascaded latch circuit. Switches S1 to S3 function as reset switches. The output at pin 10 will only transition to logic high when reed switches S4 to S6 are closed sequentially. A power transistor TR1 amplifies the current output to illuminate lamp LP1.

Instead of a pointer, a small neodymium (high-strength) magnet may be attached to one finger, and one’s finger used in place of the pointer.

In “stand-by” mode (with the lamp extinguished) the circuit will consume very little current. Therefore, a switch is not incorporated into the circuit (of course, one may be added). The box can be opened, and the battery can be simply attached or detached.