Trick++ Documentation: Magic Deck

Here’s the documentation for my Trick++ last Monday, which was constructed around a deck that had NFC chips embedded in all of the cards.

Inspiration for this trick came from several examples of computer vision/card recognition tricks I came across online, which creates an interesting performance dynamic: it’s only the computer assistant – not the magician – who knows what the chosen card is. Since I was toying with NFC communication for a separate personal project, it was a natural extension to magic tricks. NFC is obscure and new enough that most people aren’t aware of it (much less anticipate it), unlike cameras or microphones that we’ve been trained are “everywhere”. NFC was the perfect combination of secrecy and subtlety.

Actually constructing an NFC-tagged deck was more work than I anticipated. RFID decks are available online, but cost ridiculous amounts (>$100), so I was forced to build my own. I purchased a pack of 75 NFC stickers from Amazon for $40 (25-pack available here), which was still more than I’d hoped, but much more reasonable. The tags (including the plastic sticker casing) were 12x19mm and just 0.157mm thick (cards, for comparison, are just over 0.300mm), and could store 144 bytes. I found an old, low-quality deck that I wouldn’t mind losing if I messed up and was made of paper stock, not plastic. Then I got a glue stick, an Exacto knife, a needle-nose pliers, a lamp, and a long Sunday afternoon.

The process wasn’t bad once I practiced on a few Jokers (may they rest in peace). Paper stock cards are easy enough to split open from the corners, and I didn’t need cut very deep to slide the chip in with the pliers. I also alternated corners, to try to reduce the thickness increase in the final deck as much as possible. After the tag was in, I used a toothpick to “paint” the inside with glue, and then flattened out the card and put it under a heavy stack of books to set. After iterating through all 52 (miraculously without any card fatalities), I went through them again with the knife to trim any glue left on the edges. The final deck was also slightly thicker than a normal deck, so I omitted 6 cards when performing it so that it appeared the same height. Here’s the final result:


In any sort of ordinary handling, the chips are effectively invisible. If you examine each corner very closely (and get the light to catch just right), you can notice warping, although I think that is more of a result of the glue than of the chip.


The deck itself was only half of the trick. On the software side, I used a generic NFC reader-writer on the Google Play Store to write each cards’ name on it. The format I used was a two-character text string, like “4h” for the Four of Hearts or “td” for the Ten of Diamonds.

Once the cards were all encoded, I build an Android app that automatically launched itself upon contact with any of those cards, and displayed the appropriate card image. The app filters for the ACTION_NDEF_DISCOVERED intent and for text-only tags, and will launch itself whenever the phone comes in contact with one regardless of if the app is open or not (thanks Android!). The code was extremely hack-y, relied heavily on examples here and here, and I’m deeply embarrassed for ever having written it, but it is available here if anyone would like to use it for themselves. Otherwise you can get the .apk here.

Here’s a short video of the app in action:

Having created the mechanics of the trick, I then needed to construct a performance around it. I felt like I really under-utilized the potential here – there are so many possibilities that the deck opened up I hardly knew where to go to properly take advantage of its strengths.

I practices a few variations in which I would have the volunteer pick a card, which I would wave around and casually bring it near my phone in my pocket. This was rather awkward, since it’s not a natural place to leave your hand hanging, especially when it’s holding something so important. Also, “checking” my phone later on aroused a lot of suspicion.

I eventually settled on a routine built around me leaving my phone face-down on the table, then slapping the card down on top of it. Forcefully slapping things on tables seems to be a common theme in a lot of magic tricks, so it didn’t arouse too much suspicion in my practice runs – most people thought it was just showmanship, not a critical part of the trick itself. Here’s a video of one of my practice runs:

But I couldn’t just let a volunteer pick a card and then immediately slap-reveal on the phone – that would be far too obvious and, much worse, far too short for a trick like this. Instead I decided to try to purposefully obfuscate the performance so that the audience would have theories. I decided to start with a complex, unimpressive trick – a performance that would hopefully leave the audience with several theories. My original plan was to perform the same trick three times, with each repeat explicitly whittling down the possible theories until none remained. In class, on a whim (that I regret taking), I decided to only perform it twice. Here’s the final presentation, complete with spur-of-the-moment patter that tried to “explain” why I’m slapping the card down on the phone:

… “Now… It seems like some of you think this is just a magic trick. And your suspicions are well-founded – I mean, I got see the card myself, and I could have interacted with the phone in all sorts of ways. But to show you that this is, in fact, a legitimate scientific experiment, I’m going to do the trick again…”

I need to say “um” less often.

I’ll probably stick to my NFC deck for at least the midterm project, and am really searching for ideas on how to expand the presentation. How can I take full advantage of this technology?

What would you do with a magic deck?