Design Article
Control your holiday lights with a magic wand
Vladimir Rentyuk
12/16/2011 11:22 AM EST
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.
Figure 1 You can 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 and resistor R4 to make NAND gates IC1A and IC1B 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 IC2A will change its output. This enables the signal generator and a binary counter formed by IC2B, IC3A, and IC3B. 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.
Figure 1 You can 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 and resistor R4 to make NAND gates IC1A and IC1B 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 IC2A will change its output. This enables the signal generator and a binary counter formed by IC2B, IC3A, and IC3B. 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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anonymous user
12/16/2011 3:20 PM EST
This reminds me of some fun I had years ago with my grandmother. I placed the sensing wire from a Heathkit touch sensing light switch into the soil of a Schefflera plant she had in her livingroom. Touching any leaf on the plant turned on a nearby pole lamp. Touching a second time brightened the lamp, and a third touch turned it off. I had her believing that there was a particular leaf for each function, and had her memorize which was which.
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anonymous user
12/19/2011 5:37 PM EST
Terry, 'Tis the season. I am sure your grandmother story brought back many a heartwarming grandchild/ grandparent stories back to the EDN readership. I was magically transported to the beautiful valley of Kashmir in Northernmost part of India. Thanks for sharing!
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Jiri Polivka
11/28/2012 4:54 AM EST
I like the idea, but the range of the Hall sensor is quite short, not exceeding one inch.
A simple modification would replace the sensor with an IR photodiode; with an IR LED in the wand, one could control the lights (or else) over several meters (depends on optics and setting).
Over a short distance, one can also use an acoustic sensor that detects wand touching it, or, by clapping hands. Many other options. Enjoy!
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Vladimir Rentyuk
12/5/2012 3:59 AM EST
Yes, distance is short, but you should agree it is easier than acoustic relay. Using of Hall sensor is a modern version. I used a reed switch in my first design. It was it was more than 30 years ago (I designed it for my little daughter, that is why I used battery power and LEDs) and these lights for New Year’s tree properly work till today. This design was repeated many times in different variants. It is really magic for many people.
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ogdenj
12/6/2012 5:45 AM EST
I don't find using 5$ hi-tech sensor with dumb logic appealing. I suggest capacitative sense here. 1$ microcontroller with touch sensor pin oscillator will do the job. Circuit in result is ultrasimple. - uC with transistor switches and sensor itself, that's it. You don't need wand anymore, just wave your hand. Sense distances also can be up-to 10cm.
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EE UnivWA
12/14/2012 9:47 AM EST
Hi Vladimir, I'm sure every creative reader of your idea has an alternative come to mind - I like an idea that does that. One idea I saw posted was using a UV link. This would surely work, but is easily triggered by a TV remote, a glint of sunlight... I have my lab students build an IR link, and it is always the case that they discover that they can mess with each other by beaming to their sensor... lots of fun and a good lesson
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Vladimir Rentyuk
12/16/2012 3:47 PM EST
It is a nice idea, too, but it has some complication. I can give you my advice to use IC TSOP4836 (older) or TSOP34836 (modern) by Vishay as a receiver. It does not have sensitivity to much external unwanted signals. Naturally, you shall use a suitable transmitter, too. You will read about it in the Data Sheet of TSOP34836.
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