Interactive knitted shapes

A series of balls was knit on a double-bed flatbed knitting machine that incorporate conductive and resistive yarns to allow them to measure stretch, pressure, scrunch, and touch. LilyPad Arduinos and ATtiny microcontrollers were then connected to these sensors and the sensor data was sent to a computer via wired or wireless connections. Whereas interaction with a normal ball causes effect in the physical environment, interacting with these knit balls allows one to cause effect in the digital realm. To demonstrate this possibility, the sensor data taken from interaction with the knit balls is visualized and sonified. The KnitBalls explore three different types of knit sensors: resistive sensing, capacitive sensing, and resistive and capacitive sensing.

For the resistive ball, a yarn spun from a stainless steel and polyester fiber blend has been used that becomes more conductive when the fibers in the yarn are compressed to make better physical contact between the steel conductors. Compression can be achieved through pressure coming from pushing, squeezing or stretching a fabric knit from the yarn. If the material is only compressed partially between two contacts then the resistance remaining in the rest of the material stands in the way of reading the full range of the sensor.

For capacitive sensing, areas of conductive knitting are used as capacitive antennas. The human body is a conductive grounded object and as such discharges the load on the microcontroller pin connected to the conductive area. The speed of this discharge is what is being sensed and can give information about how well the body is grounded, or how close the body is to the sensing area.

Capacitive resistive sensing combines the two principles: Instead of making the contact area for capacitive sensing from a highly conductive material, one uses a variable resistive material. The readings will not only differ depending on the grounding of the human body, but also on how conductive the sensing area is because of interaction with it. As the resistive yarn becomes more conductive through being interacted with (pressed, squeezed, stretched) the capacitance readings become higher, indicating closer proximity. This method of sensing the resistance of a material through capacitance is not as reliable as resistive sensing, but one of the advantages of this method is that each sensor area only needs one point of contact.

This research was part of the “Connected Textiles” activity funded by the EIT ICT labs. With Hannah Perner Wilson and Nathalie Krüger.