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12-19-2011

Control your holiday lights with a magic wand

Vladimir Rentyuk, Zaporozhye, Ukraine

A magnet waved past a Hall-effect sensor does the trick

This circuit allows you to turn on your holiday bulbs with a wave of the magic wand. The strings flash in sequence. At the heart of the idea is the magnetic wand. It gives the appearance of real magic. The main part of the circuit is a digital magnito-resistive sensor IC4 (Figure 1). Typical Hall-effect sensors are not suitable for this design because they do not work over an extended sensing distance. They also do not switch when excited by either magnetic pole. The Honeywell 2SS52 sensor works from either the north or south pole. It has good sensitivity to a magnetic field.

Control your holiday lights with a magic wand
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Figure 1. You use a hidden magnet to toggle a Hall-effect sensor and sequence three strings of holiday lights in a binary counting progression.

You place a magnet into the end of your “magic wand.” You put sensor IC4 in the PCB or the housing of this device. The wand will work over a distance of 1 inch. R6 and C4 preset the device to an off state at power up. This RC circuit gives a high level output. This resets all the D-flip-flop triggers via the R inputs. You use capacitor C3 to make NAND gates IC1-1 and IC1-2 into a free-running oscillator. The reset circuit disables this signal generator at power up.

When you move a magic wand near sensor IC4, the trigger IC2-1 will change its output. This enables the signal generator and a binary counter formed by IC2-2, IC3-1, and IC3-2. The output drivers Q1, Q2, and Q3 will be opened by high outputs of the binary counter. The LED’s chains will sequence in a binary counting mode. You can adjust the counting frequency by changing the values of R4 and C3. A second swipe of your magic wand will toggle IC4 and the lights will turn off. You could adapt this circuit with optocouplers and ac TRIACs to drive LED lights meant for ac wall power.

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