Data Tag Cards

Using conductive ink to invisibly link physical paper with digital data

Conductive ink data tags and bare conductive electrical paint

I ordered a pot of electric paint from Bare Conductive because I was fascinated by the idea that I could just paint my own circuits. Originally, I wanted to use it on business cards to make an LED flash or something.

While I was playing with the viscous liquid, I discovered that conductive ink can be used to simulate fingers on a capacitive touch screen.

Because apparently there's a startup for everything, I then found out about TouchBase who raised $30.000 to produce and sell you conductive ink business cards.

I decided to do my own take on the technology and add a second, digital dimension to my business cards as well.

How it works

On the back of the cards, I painted rectangles on a four by four grid. The rectangles are connected with thin lines of conductive ink. It is important that the circuit touches your hand at some point.

When a person touches the card he connects the circuit to ground. When pressed onto a capacitive touchscreen, the phone recognizes the bigger rectangles as fingers touching the screen.

A selection of hand-painted conductive ink data business cards
I experimented with various ways to arrange the circuit. One goal was to minimize the chance that a ink line would be interpreted as a touch

Pattern Detection

In order to identify individual cards, I am making use of an artificial neural network.

artificial neural networks (ANNs) are computational models inspired by animals' central nervous systems (in particular the brain) that are capable of machine learning and pattern recognition.
Artificial Neural Network on Wikipedia

My experiment is written in Javascript, using the Brain neural network library for pattern detection.
Patterns are not calculated from the touch position on the screen, but from the relations between the individual touches. This way, it doesn't matter where or in which direction the card is places on the screen, which makes for a more robust detection.

A conductive ink data card in detail
Because I painted the patterns by hand, the resolution is fairly low with around 4.000 possible individual patterns. With professional manufacturing, hundreds of thousands of unique patterns would be possible.

Possible Appliances

It's interesting that the ink circuits don't have to be on the papers surface in order to be recognized. The codes could also be printed between two layers of paper, creating an invisible alternative to barcodes or QR codes.

There are less limitations compared to the aforementioned technologies because you don't need a scanner and scanning software. However, it still doesn't feel like a thing that would work on a bigger scale.

It's interesting how my paper cards or any other object equipped with conductive ink data codes get a second, digital dimensions. More information can be associated with a piece of paper than just the words or pictures on its surface.

Also, because the codes can only be read using a smartphone, the cards can also draw data from the device. Using the iPhone sensors like GPS, a piece of paper suddenly gets an exact geolocation. This opens the door for a whole range of calculations and speculations about the objects environment.