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Rob Hemsleysent in this great hack that he did using the Crayola ColorStudio HD Pen. By swapping our the stock Microchip PIC 16F505 controller with a Attiny 44 (same pinouts) he is now able to make the $30 device operate as he would like. If you are interested in doing some hacking of your own have a look at the code which is available here.
“The Crayola ColorStudio HD pen is $30 stylus device designed for use with the ipad and a custom Crayola colouring application. The intention is that you download the free drawing application which you then unlock and activate by placing your ColorStudio pen on the display. Having already made some custom PCB that use capacitive communication I immediately recognised the familiar sound of a reed relay being turned on and off when using the pen. Knowing that the device contains a relay it becomes clear how the app works, by pulsing this electromechanical component at a constant frequency this is detected by the tablet as a series of touches and distinguished from a standard finger touch.”
Crayola Pen – Hack from Rob Hemsley on Vimeo.