CaressMe is a touch sensing technology that tracks the location and strength of pressure on a 3D mold (or any surface) using capacitive sensing. This technology is created from an Arduino microcontroller, custom software using Processing, and electronics. Two prototypes were created: TouchPad, SenseBox.
The CaressMe touch technology was created for the CaressMe project, which was presented at Siggraph 2010.
About Capacitive Sensing
An RC circuit with stabilizing capacitor.
The Send and Receive pins are connected to analog output and input of the Arduino microcontroller, respectively. When the send pin changes state, it also changes the state of the Receive pin after a delay. This delay is determined by an RC time constant, R*C, where R is the value of the resistor (R3) and C is the value of the capacitor (C3) plus any other capacitance (like the human body) present at the Receive pin. A small capacitor in parallel (C6) helps to stabilize the sensed readings. Therefore, a higher Receive value can indicate closer proximity between human body (hand) and sensor.
CaressMe uses a capSense library (http://www NULL.arduino NULL.cc/playground/Main/CapSense) which toggles a Send pin and waits for the Receive pin to change states.
TouchPad
A 3D mold sits on top of the CaressMe platform. CaressMe mold is created by Melanie Cassidy.
Capacitance sensors placed in triangular formation.
A 3D mold (13 inch x 10 inch, created from plaster) sits on top of a platform that houses 3 capacitance sensors. The sensors are arranged in an equilateral triangle for triangulation.
Just three sensors can track the entire surface of the 3D mold!
The platform is suitable for housing electronics underneath. There are 3 capacitive sensing circuits under the platform, one for each sensor. Placing Arduino and circuits underneath the platform will minimize the electromagnetic interference on the sensors.
The ground plate is a sheet of aluminium foil on the bottom of the platform which is used to reduce noise.
The surface of the platform is a triangular grid which ensures the equilateral sensor arrangement. A ground plate on the bottom of the platform reduces noise, at the cost of reduced touch detection. For more efficient results, the ground plate and Touch sensors are arranged as below.
The Sensors
The physical sensors are made from copper (they can be purchased in sheets from any hobby electronics store) and about 1.5 inches in diameter. At the centre, they are soldered to regular 22 gauge wire. The wires are poked through holes in the platform in an equilateral arrangement.
The sensor head is made from copper. A wire is poke through the centre and soldered.
Please note that copper rusts with prolonged exposure to air. This means that the sensors need to be replaced. Aluminium can also be used but does not support soldering.
SenseBox
What if the 3D mold is a good insulator, too good of an insulator that the sensors cannot penetrate through the mold? The SenseBox explores an alternative sensor design – using the immediate surroundings of the mold to detect touch.
Sensors are arranged on side, back and bottom to sense x, y, and z parameters respectively.
A surrounding box enclosure can be used to detect touch. The mold sits inside of the box and 3 sensors surround it. The side, back and bottom of the box are lined with aluminium foil capacitance sensors. They give the x, y, and z (pressure) coordinates respectively. A lid for the box (not shown) protects the sensors from noise. The Arduino and circuits are meant to go in a separate compartment underneath the main mold compartment.
The Sensors
The physical sensors are made from rectangular sheets of aluminium foil. The size of the foil pieces has been calibrated to the electronics. The side and back sensors extend to the bottom of the platform.
Side: 9 in * 10 in
Back: 9 in * 13 in
Bottom: 10 in * 13 in
A similar box sensor can be found on the Instructables (http://www NULL.instructables NULL.com/id/DIY-3D-Controller/)site.