Pen-on-Paper Electronics
I spearheaded the Pen-on-Paper Electronics project at the University of Illinois in 2010. Paper has become a popular material for circuit boards because it is low-cost, lightweight, and can be rolled and folded into unique shapes. However, standard printing techniques (like roll-to-roll) are still cumbersome and expensive. What if the circuit fabrication approach was ubiquitous as paper, itself?
drawing circuits
Commercial pens are filled with a custom water and silver particle ink. The ink flows easily from the pen, and dries quickly to create an instant circuit prototype or unique electronic art.
Figure 1
Closeup images of the rollerball pen tip. The ball tip is ~0.96 mm in diameter.
Figures 1, 3, & 4 are adapted from:
A Russo, et. al, "Pen on Paper Flexible Electronics." Advanced Materials 23, (2011).
Figure 3
When printed on standard copy paper, an ink trace can be bent nearly 10,000 times to a radius of 0.5 mm before it fails. Sub-figure c) reveals that the ink fails when the paper wears out.
Figure 4
Early applications of Pen-on-Paper Electronics included electronic art, a 16x25 LED array with individually addressable pixels, and a functional RF antenna.
Pen printing dynamics
If we examine pen writing closely, we can detect a "printing instability" similar to what is found in roll-to-roll techniques. Above a certain speed, the ink meniscus splits into two streams, resulting in an ink pattern with a thin stripe down the middle. For normal writing, this doesn't matter much, but for circuit applications we prefer a single continuous trace.
The threshold speed depends on the viscosity and surface tension of the ink.
Animated gif is adapted from a pending publication
touchpad prototypes
Pen-on-Paper Electronics, combined with accessible programming tools like Arduino, can be used to prototype touch pad displays. This 5-segment pattern has 9 separate active areas.
Animated gif is adapted from a pending publication
Resistive carbon ink
In figure d) carbon ink is used as a resistor in a hand-drawn RC filter (R = 1.23 MOhms). The capacitor is created by drawing a 5mm square of silver ink and overlaying it with adhesive-backed paper and an additional layer of ink (C = 1.57 nF).
By arranging our oscilloscope probes in the top orientation, we achieve a low-pass filter; in the bottom orientation the device acts as a high-pass filter (blue = input; red = output signal).
Figure is adapted from a pending publication.
paperduino
To demonstrate the utility and range of the tool, I printed an Arduino Pro Mini board on paper using the Silhouette SD pen plotter and a Circuit Scribe pen. Once the design files are ready, this project can be constructed in <30 minutes. Full directions are in this Instructable.