Alternate Fabrication Approaches for Tangible Knobs on Capacitive Commodity Devices Alexandre G. de Siqueira1,2 Brygg Ullmer1,2 Mark Delarosa2,3 gomesde@clemson.edu bullmer@clemson.edu delarosa.mark.j@gmail.com 1Clemson University, Clemson, SC 2 Louisiana State University, Baton Rouge, LA 3 Solano Community College, Fairfield, CA ABSTRACT After decades of research and practice, the tangible interface community still contemplates the question of what tangibles might look and act like as they grow common. This paper discusses some fabrication techniques and commercial exam- ples of a class of tangibles embodied as cylinders, wheels, or knobs that can function with mass-market multi-touch devices. Figure 1. Fabricated and commercially available tangibles. Laser cut We consider laser cut knobs, 3D printed knobs, and support knob (left); 3D printed knob (center), Surface Surface Dial (right). these with several simple applications, as well as trajectories toward more applied uses. We also discuss interoperability Boxes [22]; wired, like Griffin’s PowerMate [21]; and wire- with Microsoft Surface Dials and consider future implications less, like Microsoft Surface Dials [14], Dell Canvas totens of our current work. [4], and many others. This makes the present seem an inter- esting moment to explore synergies between community and ACM Classification Keywords commercial forms. H.5.m Information Interfaces and Presentation (e.g. HCI): While some might aspire for a single standard to emerge, seek- Miscellaneous; H.6.2 User Interfaces: Input/Output Strategies ing possibilities and interoperability between many different variants may be attractive. In resonance with several academic Author Keywords and commercial approaches, we illustrate some platforms that Tangible user interfaces; capacitive touch screens; passive work on commodity multi-touch devices that inter operate knobs; dials; 3D printing; laser cutting; pattern classification with custom and commercially available knobs; and introduce variations on knobs fabricated by laser cutters, 3D printers, INTRODUCTION and variations upon commercial forms. Following the success As the number of publications investigating tangible interfaces of TUIO (www.tuio.org), we explore OSC [23] and TUIO vari- approaches 3000 (per the ACM and IEEE Digital Libraries), ants as a low-level protocol, while hoping to join others in many researchers, practitioners, educators, commercial star- considering what higher level data descriptions and protocols tups, students, and beyond are increasingly contemplating the might look like. question of what tangibles might look and act like as they grow common. Might they be general purpose, special purpose, or BACKGROUND AND RELATED WORK some combination of function? May they most often be built Tangible interfaces represent a subfield of human-computer or bought? May they best be fabricated using laser cutter, interaction (HCI) concerned with approaches for giving physi- 3D printer, by hand, or in some other fashion? We suspect a cal, interactively manipulable form to digital information. The likely answer is “yes, and ...” As illustrated by the activities of TEI, DIY, Maker Spaces, Internet of Things, among others, topic is also referred to as tangible user interfaces (TUIs) [8], momentum on all of these fronts and many more currently in the context of research investigating tangible interaction. exists, and we imagine this is likely to continue. A number of tangible-enabled systems employ dial-like tangi- bles as representations and controls for cyberphysical associa- Regarding specialized forms, perhaps a majority of publica- tions. The use of knobs in computational systems has a long tions to date explore distinctive physical forms. From a gen- history. The electromechanical interfaces of the 1946 ENIAC eral tangibles perspective, cubes, cylinders/knobs/dials/wheels, computer incorporated hundreds of radial input dials [6]. The marbles/spheres, and several other geometrical forms have re- curred as common patterns not only in the tangibles literature, mid-1950s SAGE system [2], Sutherland’s 1960s SketchPad but also going back hundreds or thousands of years, from clay system [17], and many other early graphical interfaces promi- accounting tokens [16] to Froebel’s gifts [5], and far beyond. nently incorporated interaction via mechanical dials. These early uses employed permanently mounted physical dials that Commercial industry has, especially of late, introduced many were either statically mapped to specific digital functions, or mass-market variations upon dials: fixed, like SGI’s Dial reassigned by the GUIs to which they were coupled. Figure 2. a) Detail of the top (left) and bottom (right) of a laser cut knob; Figure 3. (left) 3D printer fabricating knob. (right) Microsoft Dial and and b) the parts that compose a knob. 3D printed knob operating a control interface. Among systems conceived as tangible interfaces, tagged han- for round knobs with a flat top and bottom, indicating the dles offered interchangeable, tracked knob-like elements with affordance of rotation. haptic feedback, often used in audio contexts [10, 11, 15]. Where tagged handles were “labeled” with radial arrays of The knobs’ size is comfortably held by most teenagers and shapes and textures, the wheels of Strata/ICC [19] and tangible adults, while also being suitable and safe for children, with query interfaces [18] labeled tokens with static text and visuals, the possible exception of the very young. Knobs are ~6 cm in and applied these to parametric navigation of diverse datasets. diameter. Where [11, 19, 18] structured knobs interaction around fixed Capacitive sensing requires designing knobs in which some or mechanical constraints, Sensetable and ReacTable allowed all components are conductive. We use acrylic sheets, wood, tangibles to be sensed and graphically mediated through con- and metal shims when fabricating with laser cutters and acry- tinuous manipulation across interactive tabletops [10, 15]. lonitrile butadiene styrene (ABS), or conductive polylactic More recently, research including SLAP widgets [20] and acid (PLA) thermoplastic when 3D printing. FacetStreams [9], have evolved the visual, domain applica- tion, and implementational strategies. In other variations, the In the next sections, we present our laser cut and 3D printed smartwatch-based tokens of [1] employ new commodity plat- knobs, together with associated TUI prototypes. forms toward the realization of active knob-like tokens. Among the most common applications, tangible interfaces Design and engineering considerations have engaged elementary education [12], art and music [10], Fabricating passive knobs requires careful design and engi- and DIY/Maker Movement [13]. Many tangible interfaces neering decisions. To distinguish capacitive objects from have also engaged scientific applications [1]. We aim to bal- finger-touches, spatial [3] or temporal [24] multiplexing is ance our sample applications among these contexts. typically used. The more common of these, and the one we employ, is spatial multiplexing. Here, two or more conduc- DESIGNING THE KNOBS tive, capacitively coupled points are positioned in a distinct Our research group has a long history in developing tangible constellation relative to each other. Different systems employ interfaces. Some of these have involved electro-mechanical different numbers of contact points. This number is associated systems. In recent years, we have also emphasized general- with trade-offs including the physical size, distinguishable IDs, purpose, reproducible approaches allowing multiple knobs to number of concurrent tokens, error-resilience, required physi- be assembled faster and more uniformly than the manually cal pressure, materials and fabrication technologies employed, fabricated ones. and mobile vs. fixtured use. Our present knobs are sensed by commodity, widespread hard- Two other broader technical constraints shape the function- ware platforms that are capable of capacitive sensing, such ality of capacitive tags. First, multi-touch capacitive screens as tablets, laptops, and smart-phones; eliminating the neces- typically incorporate a number of constraints relative to their sity of custom-built or special-purpose hardware. Our design anticipated use and function. For example, most capacitive incorporates constellations of three touch points, sometimes tablets presently support a maximum of ~10 simultaneous using stylus tips, sometimes flat conductive rubber; that may sensed touches, and are presently tuned to sense contacts of be rigid or pliable. The pattern defined by each knob allows sizes comparable to fingertips. Second, any system that relies them to be uniquely identified. Position and direction can also upon electromechanical connections is influenced by a variety be sensed by the underlying software. More recently, we have of properties that govern the quality of electrical contact. A started to explore and integrate commercial variations, such as phenomenon known as switch bounce occurs whenever me- the Microsoft Surface Dial. chanical jitter causes intermittent disconnection of the circuit [2]. This temporary loss of contact is known to cause glitches Shape, Size, Materials and Context in systems that inadequately filter this form of noise. The Our knobs have been designed considering design criteria mapping and filtering employed by capacitive multi-touch de- within [7]: shape, size, materials, and usage context. vices to transform analog field input into 2D events introduces analogous artifacts. This is compounded by several challenges. In terms of shape, the use of cylindrical objects such as dials, First, some present multi-touch capacitive surfaces are glass, knobs, and wheels in computational systems has a long history, which may be scratched by metal. Second, especially if more including in the TUIs realm; This informed our design choice than three conductive tags are utilized, simple geometry and Fabrication of 3D printed knob requires no external tools, and can be printed on-site within an hour. The level of complexity of a 3D printed knob design is limited to that of one’s 3D printer and CAD (Computer Aided Design) skills. In terms of the number of components, our laser cut design Figure 4. (a) Matching Blocks application. (b) Creating scene with the requires the assembly of nine distinct components, while the Collage software (c) Knob used with the VideoPlayer application. 3D printed counterpart (in its simplest form) consists of only two distinct components and four parts in total. Figure 5 shows a comparison between the number of parts required by each mechanics suggests all points may not be in constant contact design and fabrication technology. with the sensing surface. Three different 3D printers were used in the fabrication of LASER CUT KNOBS our knobs: The mono-extruder Lulzbot Taz, the dual-extruder Fig 2 depicts a knob fabricated with a laser cutter. In our ap- Makerbot Replicator 2X, and a Voxel8 machine (www.voxel8. proach, we sandwich a central conductive ring, used to estab- com). With the Lulzbot and Makerbot, we used conductive lish electrical contact with a user’s hand, with non-conductive PLA for the body of knobs. With the Voxel8 knobs were layers. These outer layers support human legibility (the up- fabricated with non-conductive ABS; 3D printed “wires” made per visually-inscribed layer) and computational legibility (the of conductive silver ink coupled the touch of a user to the lower layer). The lower layer structures a constellation of capacitive display. The silver ink also has the capacity of touch points, realized as threaded conductive mesh stylus tips. connecting embedded hardware. Figure 3 shows a knob being The pattern described by these tips is defined by an acrylic 3D printed. For customization, an acrylic ring and a faceplate guide piece that is positioned within the internal circumference were added to the 3D printed knobs. of the metallic ring. The non-conductive layers also serve as SAMPLE APPLICATIONS mechanical fixture plates for connecting the ensemble struc- Several small applications have been developed to demon- ture together. The pieces are held together by three pairs of strate the knobs. All three applications presented here have rivets and screws. been tested on Microsoft Surface tablets, Lenovo laptops with The small size of the pieces employed suggests this design capacitive touch screens, and Dell 27" multi-touch displays. can be replicated with most laser cutters, as well as other fabrication tools (e.g., CNC mills and routers, water jets, etc.) Matching Blocks, Collage, and VideoPlayer from a variety of materials. Figure 5 lists the parts involved. The Matching Blocks application, depicted in Figure 4(a), was inspired by children’s toys that require fitting objects, eg. blocks of wood into corresponding slots. The goal is to 3D PRINTED KNOBS match the geometric figures of knobs with the figures on the While our first-generation approach seemed altogether effec- GUI. Visual and auditory feedback is given in response to the tive, the fabrication and assembly of the multiple components actions of the user. Six distinct knobs are used by application. could be laborious, our design was sometimes heavy, and not Faceplates made of balsa, a type of soft wood, were added for all groups have access to laser cutters. The rise of 3D print- decoration. The knobs’ body is made of acrylic of a variety of ers interested us in their potential as an alternative approach. colors in an attempt to appeal to children’s eyes. 3D printing, also known as additive manufacturing, offers a new platform for creating knobs and tangibles in general. The The Collage application works as a set of stamps, as shown three-dimensional body of a knob is generated by “slicing” the in figure 4(b). Each stamp is represented by a knob. Users virtual model into two-dimensional segments and then printing can stamp the images anywhere on screen, any number of the actual object layer by layer. times. First users "stamp" a background then they add different elements to the scene such as a house, a dog, trees or apples. The wooden knobs used by Collage are slightly lighter than the acrylic ones, requiring users to apply pressure for detection. This turned out to be a feature for our application by emulating more realistically a real rubber stamp. The VideoPlayer, shown in figure 4(c), is a TUI for video playback. Some knobs are containers of video files and others are playback controls. Besides detection and identification, the rotation of knobs controls discrete and continuous vari- ables. We explore a combination of finger touches and knob actions. A video can be moved around by touch, but can only be controlled by using one of the physical knobs. TUIO PROTOCOL TUIO is an open framework that defines a common protocol Figure 5. Comparison between laser cut and 3D printed knobs. Laser cut knobs require nine distinct parts while 3D printed only two. and API for tangible multi-touch surfaces. We use a slightly modified version of the TUIO 2.0 protocol for 2D tokens. Our computer for the SAGE System. IBM Journal of version better suits our needs without any additional parame- Research and Development 1, 1 (1957), 76–83. ters. A typical message is encoded as follows: 3. Rachel Blagojevic, Xiliang Chen, Ryan Tan, Robert /tuios/tok s i x y a p Sheehan, and Beryl Plimmer. 2012. Using tangible Here ‘s’ is a knob id; ‘i’ is the pattern id of the knob; ‘x,y’ drawing tools on a capacitive multi-touch display. In position of the knob on the screen; ‘a’ current angle of a knob, Proc. of the 26th Annual BCS Interaction Specialist and ‘p’ a boolean indicating if a knob is placed on screen. Group Conference on People and Computers. British Computer Society, 315–320. COMMERCIAL KNOBS 4. Dell. 2017. Dell:Canvas. (April 12, 2017). Recent mass-market commercial variations of knobs such as www.cnet.com/products/dell-canvas-27 the Microsoft Surface Dials [14] and Dell Canvas’ totens [4], with their native integration with the Windows 10 operating 5. Friedrich Froebel. 1899. Pedagogics of the Kindergarten. system, motivated us to seek interoperability between these 6. Herman H Goldstine and Adele Goldstine. 1946. The devices and our platforms. electronic numerical integrator and computer (ENIAC). We are interested in integration achieved purely by software, Journal of Mathematical Tables and Other Aids to or by performing small modifications. We have integrated Computation 2, 15 (1946), 97–110. unmodified Microsoft Dials to our applications running on 7. Lars Erik Holmquist, Johan Redström, and Peter Microsoft Surface Studio machines, and slightly modified Di- Ljungstrand. 1999. Token-based access to digital als running on any Windows 10 machine. Our modification information. In International Symposium on Handheld includes adding the pattern of touch points to the Dials. Figure and Ubiquitous Computing. Springer, 234–245. 3 depicts a tablet using a Microsoft Dial as a control knob. 8. H. Ishii and B. Ullmer. 1997. Tangible Bits: Towards CONCLUSION AND FUTURE WORK Seamless Interfaces between People, Bits and Atoms. In We have introduced our work on variations of knobs fabricated Proc. of CHI’97. ACM, 234–241. with laser cutters, 3D printers, and commercial forms. We 9. Hans-Christian Jetter, Jens Gerken, Michael Zöllner, showed prototypes that work on mass-market multi-touch sys- Harald Reiterer, and Natasa Milic-Frayling. 2011. tems, capable of interoperability with custom-made and com- Materializing the query with facet-streams: a hybrid mercial dial devices. We do not perceive any single technology surface for collaborative search on tabletops. In Proc. of as intrinsically better; instead, we see the future populated by CHI’11. ACM, 3013–3022. combinations and hybrids of these and other variations. Cur- rently, our work focuses on passive knobs but we hope to 10. Sergi Jordà, Günter Geiger, Marcos Alonso, and Martin soon integrate active ones; either by fabricating custom ac- Kaltenbrunner. 2007. The reacTable: exploring the tive knobs, integrating and modifying commercial variations, synergy between live music performance and tabletop or integrating knobs and higher level data description proto- tangible interfaces. In Proc. of TEI’07. ACM, 139–146. cols already existing and under development in the tangibles 11. Karon E. MacLean, Scott S. Snibbe, and Golan Levin. research community. 2000. Tagged handles: merging discrete and continuous manual control. In Proc of CHI ’00. ACM, 225–232. We look forward not only to the opportunity of sharing our work but also to prospects for working with other research 12. Paul Marshall. 2007. Do tangible interfaces enhance groups; giving, receiving feedback, forging partnerships and, learning?. In Proc. of TEI’01. ACM, 163–170. in this manner, contribute to the lively tangibles community. 13. David A. Mellis, Sam Jacoby, Leah Buechley, Hannah ACKNOWLEDGMENTS Perner-Wilson, and Jie Qi. 2013. Microcontrollers As Material: Crafting Circuits with Paper, Conductive Ink, This research was partially supported by the National Science Electronic Components, and an "Untoolkit". In Proc. of Foundation under award CNS-1126739 with additional sup- TEI’13. ACM, 83–90. port from Louisiana State University, Clemson University and the Coordination for the Improvement of Higher Education 14. Microsoft. 2017. Surface Dial. (April 12, 2017). www. Personnel (CAPES). We thank our colleagues from the NSF microsoft.com/en-us/surface/accessories/surface-dial REU program at Louisiana State University who provided 15. J. Patten, H. Ishii, J. Hines, and G. Pangaro. 2001. insight that greatly assisted the research. Sensetable: a wireless object tracking platform for tangible user interfaces. In Proc. of the SIGCHI REFERENCES conference on Human factors in computing systems. 1. Ahmed Sabbir Arif, Roozbeh Manshaei, Sean Delong, ACM, 253–260. Brien East, Matthew Kyan, and Ali Mazalek. 2016. Sparse Tangibles: Collaborative exploration of gene 16. D. Schmandt-Besserat. 2007. When Writing Met Art: networks using active tangibles and interactive tabletops. From Symbol to Story. University of Texas Press. In Proc. of TEI’16. ACM, 287–295. 17. Ivan E Sutherland. 1964. Sketchpad: a man-machine 2. MM Astrahan, B Housman, JF Jacobs, RP Mayer, and graphical communication system. In Proc. of the SHARE WH Thomas. 1957. Logical design of the digital design automation workshop. ACM, 6–329. 18. B. Ullmer, H. Ishii, and R.J.K. Jacob. 2003. Tangible query interfaces: physically constrained tokens for manipulating database queries. In Proc. of INTERACT’03. 279–286. 19. Brygg Ullmer, Elizabeth Kim, Axel Kilian, Steve Gray, and Hiroshi Ishii. 2001. Strata/ICC: physical models as computational interfaces. In Proc. of CHI ’01 extended abstracts on Human factors in computing systems. ACM, 373–374. 20. Malte Weiss, Roger Jennings, Ramsin Khoshabeh, Jan Borchers, Julie Wagner, Yvonne Jansen, and James D Hollan. 2009. SLAP widgets: bridging the gap between virtual and physical controls on tabletops. In Proc. of CHI’09 Extended Abstracts on Human Factors in Computing Systems. ACM, 3229–3234. 21. Wikipedia. 2017a. Griffin:PowerMate. (April 12, 2017). https://en.wikipedia.org/wiki/Griffin_PowerMate 22. Wikipedia. 2017b. SGI:Dial Box. (April 12, 2017). https://en.wikipedia.org/wiki/Dial_box 23. Matthew Wright. 2005. Open sound control: an enabling technology for musical networking. Journal of Organized Sound 10, 03 (2005), 193–200. 24. Neng-Hao Yu, Li-Wei Chan, Seng Yong Lau, Sung-Sheng Tsai, I-Chun Hsiao, Dian-Je Tsai, Fang-I Hsiao, Lung-Pan Cheng, Mike Chen, Polly Huang, and others. 2011. TUIC: enabling tangible interaction on capacitive multi-touch displays. In Proc. of CHI’11. ACM, 2995–3004.