POV Midair Magic

Wave the magic wand and chant “Umba gadda boomba, …” in a dark room.  A person’s name is spelled out in mid air. Persistence of vision has become a fad that seems to be lasting.  The Mad Wrapper was ahead of the times on this one. In 1991 few people had ever seen one of these.  Credit goes to the Museum of Science in Boston for giving me the idea for this great event in TMW history.

Under the tree are various packages are found all wrapped similarly with a computer chip attached.  When this chip is inserted into a socket on the decoder and the decoder is waved around in the dark, a person’s name floats in mid-air.  It is quite magical.

This is one of the best magic tricks The Mad Wrapper
has ever performed.  TMW built an LED persistence of vision wand that spells out a person’s name. The Christmas performance opens with a mysterious chant that is uttered within a darkened room and crescendos to a dazzling electronic light show that will blow your mind. This trick will be the subject of conversations for many years after.

Concealed within the decorated box marked “From the Mad Wrapper” is a decoder — a box. Inside the box there some fairly simple electronic circuits that I will explain. Outside the box is a thin strip of lights and an empty zero-insertion-force (ZIF) connector that will hold an integrated circuit (IC chip).

Simple POV

Scattered all around the base of the tree is a variety of similarly wrapped gifts — one for each participant. Each of these gifts is decorated with a ribbon and an integrated circuit. This IC is the correct size and has the same number of pins as the ZIF connector on the mysterious electronic box.

Arduino Would Have Made it Easier

More than years ago when The Mad Wrapper first created this marvel, Arduino did not exist.  The electronic components of the time were much less sophisticated and required more skill to perfect.  The advent of Arduino has hugely simplified electronics projects like this one.  Now the curious layperson is almost fully empowered to create anything out of a dream.  The future of Mad Wrappers across the globe has become a whole lot brighter.

There is a fantastic website that presents recipes for pretty much any gadget thinkable.  In particular there are a bunch of examples of POV.  The simplest one may actually be the best one.  Take a look at http://www.instructables.com/id/Simple-Arduino-POV-/ . After reviewing that page, feel free to skim or skip the details on my page that describes twenty-year-old technology.

Before Arduino: Doing it the Old Fashioned Way

Before the availability of microcomputers on the mass market (e.g. Arduino) a project like this required some electronics skill.  If you have some experience with electronics, the effect is phenomenal and well worth the effort.  As electronic circuits go, this is a pretty simple circuit.

The integrated circuit (IC) attached to each gift is a programmable ROM that contains the sequence of on/off signals on each output pin.  The output pins are each connected directly to each of 8 LEDs.  By cycling repeatedly through the data in the ROM, the LEDs flash on and off to form letters.

Not sure if the following explanation is helpful but I will try to put it into layman’s terms.

Concealed inside the case of the decoder box are a few computer chips and a mess of wires. There are four sections of the circuit: a clock, a counter, memory, and LED lights.

  1. The clock simply keeps the beat — just like a drummer in a band. The counter counts. This guy makes numbers.
  2. Every time the clock hits a beat, the counter makes a new number: 0, 1, 2, 3, 4, 5, 6, ….  Always counting up until it gets to 255.  Then it resets and begins counting from zero again.
  3. This number is presented to the input of the read only memory (ROM).
  4. The ROM memory is simply a lookup table of numbers.
    1. At address 0 the number represents the first column of LEDs that need to be on to start the first letter of the person’s name.
    2. At address 1 the number is the next column of “on” LEDs in the letter.
    3. For a 6×8 font, the 6th location (location 5) on the ROM contains the last column of the first character.
    4. Then a few zeros to turn off all LEDs to create a gap between letters.
    5. And the sequence continues until the name is spelled to completion.
  5. Red LED’s will briefly glow based on the voltage on one of the output pins of the ROM at any given moment.

If you fill the memory with the right sequence of numbers to generate a message then the counter needs to simply count up so the lookup table inside the memory chip produces the message you want.

Thank You MOS!

Circuit Without Clock

I first saw a gadget similar to this at the Boston Museum of Science in the early-1990’s. Upon returning home I immediately set out to built one for Christmas time. The design of the electronics was simple since it required only minor modifications to a Morse Code sequencer that I had built a couple of years earlier. The hard part was planning out the letters on graph paper. When I showed the first implementation to my best friend, Daver, he was very impressed with how it well it worked but was disappointed in the letters I designed so he wrote me a program to convert any Amiga computer font into a form that I could use for the decoder. All of a sudden the hard part of the project was trying to decide which font to use. There are a lot of fonts designed to work on an Amiga computer. Finally I decided on a font. The change was amazing. The mid-air message really came alive. I am once again indebted to Daver for his help on this project.

Sort of a Simple Computer

Most people understand little about how a computer works. Many people are very curious how they work but have never had the opportunity to learn. This is a great project to learn the mysteries of computers.

While this flasher is not actually a computer, it has many of the major features found inside all the true computers that many people may want to think of this as a simple computer. It is a good analogy.

After I had the gadget running with some simplistic lettering. It was not until many years later that I started seeing these for sale here and there. Now, more than ten years later I see these everywhere and in various forms. There are holiday messages on the tips of whirligigs at joke shops. There are words on pendulums sold at museum shops. And there are ghostly mid-air clocks on sale and spinning on display at up-scale gadget stores.

This really does feel like magic. To some, the result is so bizarre that it really takes some explaining to convince them that it is not magic. This project requires a fair amount of electronics knowledge, but the circuitry is no more complicated than the Morse Code design described earlier in a previous chapter. Just like many food recipes are based on one or two fundamental recipes, most of the electronics that the Mad Wrapper has built are fundamentally the same project. If you know how to make vanilla ice cream, it is easy to figure out how to make chocolate ice cream. Although chocolate and vanilla may appear to be such distant opposites, these two types of ice cream are fundamentally the same. If you have built a Morse Code flasher, you can easily build a sky-writer. The two gadgets are nearly identical by design, but they are worlds apart in effect.

I would urge anyone who has some knowledge of electronic circuitry to do first build the Morse Code project, then follow it up by building this project. The result is fantastic.

The Christmas Chant

A strange chant teaches everyone to wave the Decoder around a darkened room. Magically the flashing LEDs transform into a person’s name streaking across the room in brief mid-air displays of lighting theatrics. Very exciting! Best one yet!

The following instructions were left for guests to follow.  Basic interpretation: connect the thing found on the present to the socket found on the POV device.  Then wave it around in the dark to see a name.

Magic is in the air! Long, long ago a small wizard was once professed
to say that many secrets may be held within the most innocent of

If approached in the correct manner. During the week of a new moon, a
person might encounter a box of small proportions and become
suspicious. During that same week, should a gentleman of either sex
discover coincidentally a small stone of unique proportions such that
it might merry with the discovered box, then suspicion will most
certainly arise from the very confines of any mans heart.

Before unlocking the secrets dear to every man's heart, certain
preparation must be made. A séance must be observed, and it must be
observed properly.

Darken the chamber for all who dares to enter its realm. A single ray
could break the spell and be forever forgotten. It is important that
all who are there shall assist. Stand in a ring around the two
objects. Join hands and repeat aloud the following:

 Umba gadda boomba, gadda gadda boom.
 Maaaa, maaaa, aaaa, aaaa, maambaa.

This is very important. The spirits within will begin to stir.

While all who are present, continue to chant, the king of all in the
room will search the walls for two small parallel vertical slots to
which the box is to be connected. This will spark terror in the demons
within the box. They will begin to scurry, trying to find a way to

 Umba gadda boomba, gadda gadda boom.
 Maaaa, maaaa, aaaa, aaaa, maambaa.

In a fit of passion, unite the stone and the box to spread fire across
the room. Begin to chant faster and faster. Pick up the box and wave
it wildly to the rhythms in the room. The demons will escape with a
message for all to see.

 Yup, everyone actually crowded around in the dark and chanted as directed.  This was a time before POV was popular in the stores  at the mall so few in the  room had actually ever experienced it before.  It was a magical moment.  An experience talked about for decades after.

Definitely among the alltime best Mad unwrappings.

Background: How the POV Illusion Works

Almost every home in America holds at least a few gadgets with LED numerical displays. Most of the older calculators presented their answers with Light Emitting Diodes. Many digital alarm clocks glow through the night with LED numbers. VCRs and wall ovens also often show time and other data with LCD panels. Battery powered rechargeable devices nearly always light an LED indicator when plugged in. Many portable devices will light an LED to indicate that power is on.

You might be surprised to discover that about half of these devices blink. Tonight darken your house and move from room to room gazing the various red, green and yellow glowing LEDs. The LED should appear bright against a backdrop of darkness. If you encounter a portable device, pick it up and shake it. If you encounter a larger glowing object, gaze at it but shift your eyes quickly from side to side. Sometimes it is easier to see the effect through a small hand-held mirror. Gaze backwards at the reflection, then shake the mirror tipping it from side to side.

With everything in motion you might see long unbroken sharply focused streaks or lines running across the room. These LEDs are not blinking. Or you might see a long stream of highly focused dashes or separated lettering that replicates the time, calculation, or whatever message your display might show. These LEDs are blinking.

Consider the blinking repeating messages. We have letters, and we have gaps. The letters appear when the LEDs are on. The gaps appear when the LEDs are off. By moving the device or by moving your eyes between flashes, the letters jump around from place to place. It is a bit magical but it makes sense.

Your household devices do not change their messages between flashes, but what if they did?

If you wave an unblinking LED around in a dark room, you would get a continuous streak of light. Now, take that same LED in the dark room and wave it back and forth behind a set of vertical bars. You would see long dotted lines. Now, make the LED blink rapidly. What would you see? Same thing: long dotted lines. Think about it.

Now take two unblinking LED’s. Put them side by side and wave them about the room. You’ll see two long streaks of light. Make them blink and you see two dotted lines. Now, think about what would happen if the two lights blink at different rhythms. You would see two dotted lines which kind of make a pattern in the air.

OK so far? Go back and read that last paragraph.

Now here’s how it works. If you take 8 blinking LED’s all blinking at different rates you’d begin to see some interesting patterns. If you can control each LED to time it to blink at just the right time in a sequence next to all the other LED’s, you could make interesting patterns in the air. The circuit I describe below will control the LED’s in such a way that the pattern in the air becomes letters and words.

The circuit is, for all intents and purposes, the same circuit as was built during the Christmas of Morse code. There couple of components which form a clock circuit which sends pulses to a chip which simply counts up from zero to 255. By hooking this counter, pin for pin, to a programmable ROM memory chip, and hooking the memory output, pin for pin to a set of LED’s, the LED’s will flash on and off in the exact order of whatever is programmed into the memory. I would urge the reader to build the Morse code circuit first. It’s the same circuit but slightly easier to understand mainly because it runs slow enough to make the concepts easier to understand.