Publication: T. D. Ta, F. Okuya, Y. Kawahara, LightTrace: Auto-router for Designing LED Based Applications with Conductive Inkjet Printing”, Proc. of ACM SCF ’17, Article No. 3. DOI: 10.1145/3083157.3083160, Jun. 2017.

Combination of graphic design and printable electronic circuits has brought rich featured elements to the creation of interactive applications. Designers wish to focus on creative and aesthetic aspect while making such circuits. But current technology forces designers to think about complicated electrical behavior of the circuits which is discouraging. Even a simple application as driving a bunch of LEDs with conductive ink also causes troubles unique to conductive inks. Due to relatively higher resistance of conductive ink, it is difficult to come up with a pattern that lights up the LEDs evenly. Wiring a large number of LEDs is not straight-forward and error-prone. Electronic circuit designers often use built-in auto-routers of Computer Aided Design tools to route electronic circuit boards. However, these auto-routers usually assume that resistance of metal pattern is trivial. This is not applicable in case of conductive ink. When we design LED-based applications using traditional bulk metal wiring (copper in PCB), ballast resistors are employed to protect and assure that all LEDs light up. However, when using conductive ink for the same applications, the resistance of the conductive ink can be used and eliminate these ballast resistors. Our proposal, LightTrace, is an LED auto-router in Adobe Illustrator. LightTrace computationally designs conductive patterns, adjusts its resistance to connect LEDs so that all of them will light up evenly in a single layer sheet of paper without any additional resistors. We use the Traveling Salesman Problem algorithm to achieve the shortest and cross-less path through all LEDs, thus reduces the amount of ink needed.

A circuit of multiple LEDs routed by Eagle, and wired on a PCB. Some LEDs get very high current and become hotter which results in changing of emitting light color. Eventually, these overcurrent LEDs will be burnt up.

“AB” text with silver ink circuit routed by existing autoroutes (Eagle). LEDs light up unevenly.
“AB” text with silver ink circuit routed by our autorouter. All LEDs light up uniformly.

Route multiple characters

The circuit is printed with silver nano-particle ink.

Frowning emoji

Smiling Emoji

Summer night fireflies artwork

Night sky artwork