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Accelerometer Based 3D Mouse

Accelerometer Based 3D Mouse

Bernard shows us how to use an use an accelerometer as a mouse. This project uses a MEMS X or Y accelerometer, a PIC microcontroller and a old mouse. He also describes a trick for powering the new mouse with the unused RS232 serial control lines
This project demonstrates the use of a accelerometer as a computer mouse, but first what is an accelerometer? Its a device that can measure acceleration and the pull of gravity. There are multiple ways of doing this, the particular one I’m using works with the capacitive method. Inside the chip is a capacitor with an extra plate in the middle that can move. As you know the closer the objects are together the bigger the capacitance, the circuit inside the chip measures the capacitance difference between the two plates and the middle one. Finally the circuit coverts this in to a analog signal between 0V and 3.3 V. All of this is small enough to fit in to a small SMD chip.

The accelerometer used in this project is MMA6270 manufactured by Freescale Semiconductor. It has two sensors inside the chip, each facing at 90 ° to each other providing the X and Y axis. This is perfect for a mouse. In this case we are using it to detect the angle of the mouse. When the mouse is completely horizontal bough X and Y have 0G applied to them, but when we tilt the mouse the gravitational pull starts to cause force on the axis. But we wanted to move the mouse cursor using this. So we put on a PIC microcontroller, connect all the outputs to the ADCs and send the data over to the PC

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