Printing Acoustic Interfaces
Instructor: Clemens Wegener
Credits: 6 ECTS, 2 SWS
Capacity: max. 12 students
Location: Marienstrasse 7B, R002
First Meeting: 9th April 2019, 9:15 AM
This course focuses on printing acoustic sensors for the sensing of structure-born sound. Print processes like silver ink-jet and screen printing can be applied to manufacture acoustic sensors. Tapping and sliding gestures on an acoustic surface have a different sound impact, which can be leveraged to design new interaction concepts. The course focuses on developing a concept for acoustic interaction and developing a working prototype with appropriate sensors and signal processing abilities to materialize your concepts.
Knowledge in Hard- and Software would be highly appreciated, but is not a requirement.The needed functional components will be explained throughout the course. In parallel you will develope your own interaction concepts or product prototypes. For buying electronic components, a little budget of 10€ to 20€ is neccessary. Of course you can keep your manufactured works.
Successful completion of the course is dependent on regular attendance, active participation, completion of assignments, delivery of a relevant semester prototype and documentation. Please refer to the Evaluation Rubric for more details.
Here you find learning material in the form of circuit simulations, that lead you to the understanding of amplifiers and other signal conditioning circuits that we use throughout the course. Feel free to experiment with them, they are editable and saved via the encoded URLuniform resource locator – a human readable web address which is looked up by the →DNS and translated into an →IP Address. You cannot destroy them and it is easy to share edited versions. Here is an introduction to the circuit simulator.
To get rid of our big magnets, we build an electro magnet with the help a a sending coil that will build up a magnetic field. When the current though this sending coil changes, it will induce a magnetic field, that we can use to induce a current in the second (receiving) coil. Two coils that share their magnetic flux via the air are called an "air core transformer". Both coils will be printed on paper, but on different sheets, leaving a gap filled with air. If the sheets are close together the second coil induces more current and lesser when it is further away. It is important, that the currents change constantly, because only changing currents can induce magnetic fields. We will use a high frequency changing current (50Khz) on the sending coil, that we will receive on the other coil. When we change the distance between the coils, the actual amplitude (volume) of this high frequency tone increases or decreases. To get the actual volume information of this high frequency tone, we use the half wave rectifier. This circuit is commonly used in radio signal receivers, where the amplitude of the the frequency of a radio station is changing with the actual transmitted sound wave. This is called Amplitude Modulation (AM Radio).
To send the high frequency current, we will use the 555 Timer chip configured as a square wave generator. This circuit has little components and is comparably easy to build. It uses only one capacitor and one resistor to set the frequency of the square wave. You can find the circuit in the link below. Be sure to match the pinout in the circuit according to the figure on the left.
When we change the distance between the coils in our paper built air core transformer, the actual amplitude (volume) of the high frequency tone increases or decreases. To get the actual volume information of this high frequency tone, we use the half wave rectifier. The circuit consists of a diode, a resistor and a capacitor. The diode lets only the positive current travel through it (in the direction implied by the arrow) and blocks the negative current, running against its direction. This leaves us with the positive half of the sending waveform. The final thing we need to do is average this positive half wave to get the average amplitude of this half wave. This averaging is achieved by the capacitor and the resistor. When the capacitor is charged, and there is no voltage on the right side of the diode, a discharge current will flow through the resistor to ground. The amount of discharge current is controlled by the resistor. The bigger the resistance the less discharge current will flow. We need to adapt the value of this resistor to have the capacitor discharge just a little bit, before the next positive half wave arrives at the right side of the diode. Then, if we receive less current in the second coil, the average charge on the capacitor decreases, following the actual acoustic waveform between our two sheets of paper.
Suganuma, Katsuaki: Introduction to Printed Electronics. New York: Springer Science+Business Media, 2014.
Y. Kawahara, S. Hodges, N. Gong, S. Olberding and J. Steimle, "Building Functional Prototypes Using Conductive Inkjet Printing," in IEEE Pervasive Computing, vol. 13, no. 3, pp. 30-38, July-Sept. 2014.
Jones, Randy & Driessen, Peter & Schloss, W & Tzanetakis, George. (2019). A Force-Sensitive Surface for Intimate Control.
Inspiration for your prototpyes: