Detection

Let’s present you the interactive part of Roled’s Cube!

To interact with the cube, the team worked on two different sensors: capacitive presence sensors just around the cube, and a Kinect camera.

The presence sensors use the principle of capacitive detection. It uses the fact that when we put our hand near an electric wire we increase the capacitance of the wire. So, we have linked together two GPIOs (general purpose input/output, or pin) of the micro-controller and we have put a huge resistance between them (around 4 mega-ohms). You can see this circuit on the image just beneath (picture 1, picture credit: http://playground.arduino.cc). We raised one of the GPIO from 0V to 3,3V, and we calculate the time it takes to the second GPIO to switches from 0 to 3,3V. Because this time is equal to R*C (resistance by capacitance of the circuit), and that C increases if we put our hand, a raise in this propagation time signifies that a hand is nearby our sensors. To realize the operation on the two GPIOs, we use ATtiny85, that we have put on very small PCB, on every face of the cube (see picture 2 beneath). These ATtiny communicate with the STM32F405 via a protocol based on I2C.

Picture 1: capacitance captors.

Moreover, the team develop a small application with a Kinect camera: it is now easy to control a point in the cube just with your hand. Look at this feature on the following video!

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