22-12-2012, 05:11 PM
ACCELEROMETER MOUSE
[attachment=44997]
Abstract
[Many tasks that are performed on the computer require the use of both a keyboard on the
mouse, and many people find it frustrating and awkward to have to switch back and forth
between them. The air mouse can be a great solution for this.] As computers have
evolved from 66MHz to the 3+GHz today, the mouse has remained relatively unchanged.
There have been only two major changes to the mouse since its inception: more buttons,
and interface changes (PS/2, USB, Wireless) but the core interaction method has not
changed. The touch pad mouse and the stick mouse have been designed for a laptop, but
have not gained momentum outside of laptops.[ And most laptop users usually carry a
USB mouse with the laptop as well.]
The accelerometer based mouse can be treated as the new age input device. It is more
natural in its feel and provides the user with better ease of use. The user interface of
applications can be changed to utilize the free hand movement possible with the device.
Introduction
The aim behind the project is to be able to sense the movement of a user’s
hand and use it to control the movement of mouse on screen. For sensing
hand movement, we use an accelerometer. This would give us the
acceleration sensed by the device in each axis. We use this data to find the
change in movement of mouse pointer, which is then transmitted serially to
the host computer using RS 232 communication.
High Level Design
We are using accelerometer to measure the acceleration of a user's hand and integrate that
acceleration into a change in position. The math behind this is very easy - using Verlet
Integration, we would approximate the integral of the acceleration to the second degree.
Verlet integration interpolates between to measured accelerations, using the average
slope between them to derive velocity. This is sometimes called "trapezoidal integraton."
Here are the equations:
x(n)= x(n-1)+ v(n-1)Δt + 1/2αΔt²
But gravity would affect the accelerometers for sure , this acceleration would be added
into the integral, and with no negative acceleration to remove it, the change in position
would grow boundlessly.
Because of this, we decided to construct a tilt mouse instead. While not as
impressive as a position tracking device, the tilt mouse is easy to use and almost as neat
as a position tracking mouse. The math behind this scheme is very easy - measure the
acceleration due to gravity on the mouse, and multiply this by some constant to scale
your output to a desirable level. The Microsoft serial mouse protocol uses an 8-bit twos
complement number scheme to send data to the computer, and the numbers outputted by
the Atmel Mega32's analog-to-digital converter can be conveniently represented in the
same number of bits. However, the numbers outputted by the accelerometer had to be
altered to normalize voltage extremes to -128 and 127 and the accelerometer's neutral
output to 0. In addition to scaling the output, we also used a step filter on the data to
make the mouse easier to use. Our accelerometer was so sensitive that the slightest
motion of one's hand would cause the device to output a nonzero acceleration. To give
the user a more stable region around the zero point, we quantized all outputs below a
certain level to 0, then normalized any outputs out of this cutoff range by the breadth of
the cutoff range. For example, if the cutoff were abs(10), the intersection of all numbers >
-10 and all numbers < 10 defined the cutoff region, and any outputs outside of this range
would be normalized by +10 or -10, depending on whether the output were negative or
positive, respectively.
Hardware Design
We used the MMA7260QT accelerometer from Freescale Semiconductors. It is a low
cost capacitive micromachined accelerometer features signal conditioning, a 1-pole low
pass filter, temperature compensation and g-Select which allows for the selection among
4 sensitivities. Zero-g offset full scale span and filter cut-off are factory set and require no
external devices. Includes a Sleep Mode that makes it ideal for handheld battery powered
electronics.
[attachment=44997]
Abstract
[Many tasks that are performed on the computer require the use of both a keyboard on the
mouse, and many people find it frustrating and awkward to have to switch back and forth
between them. The air mouse can be a great solution for this.] As computers have
evolved from 66MHz to the 3+GHz today, the mouse has remained relatively unchanged.
There have been only two major changes to the mouse since its inception: more buttons,
and interface changes (PS/2, USB, Wireless) but the core interaction method has not
changed. The touch pad mouse and the stick mouse have been designed for a laptop, but
have not gained momentum outside of laptops.[ And most laptop users usually carry a
USB mouse with the laptop as well.]
The accelerometer based mouse can be treated as the new age input device. It is more
natural in its feel and provides the user with better ease of use. The user interface of
applications can be changed to utilize the free hand movement possible with the device.
Introduction
The aim behind the project is to be able to sense the movement of a user’s
hand and use it to control the movement of mouse on screen. For sensing
hand movement, we use an accelerometer. This would give us the
acceleration sensed by the device in each axis. We use this data to find the
change in movement of mouse pointer, which is then transmitted serially to
the host computer using RS 232 communication.
High Level Design
We are using accelerometer to measure the acceleration of a user's hand and integrate that
acceleration into a change in position. The math behind this is very easy - using Verlet
Integration, we would approximate the integral of the acceleration to the second degree.
Verlet integration interpolates between to measured accelerations, using the average
slope between them to derive velocity. This is sometimes called "trapezoidal integraton."
Here are the equations:
x(n)= x(n-1)+ v(n-1)Δt + 1/2αΔt²
But gravity would affect the accelerometers for sure , this acceleration would be added
into the integral, and with no negative acceleration to remove it, the change in position
would grow boundlessly.
Because of this, we decided to construct a tilt mouse instead. While not as
impressive as a position tracking device, the tilt mouse is easy to use and almost as neat
as a position tracking mouse. The math behind this scheme is very easy - measure the
acceleration due to gravity on the mouse, and multiply this by some constant to scale
your output to a desirable level. The Microsoft serial mouse protocol uses an 8-bit twos
complement number scheme to send data to the computer, and the numbers outputted by
the Atmel Mega32's analog-to-digital converter can be conveniently represented in the
same number of bits. However, the numbers outputted by the accelerometer had to be
altered to normalize voltage extremes to -128 and 127 and the accelerometer's neutral
output to 0. In addition to scaling the output, we also used a step filter on the data to
make the mouse easier to use. Our accelerometer was so sensitive that the slightest
motion of one's hand would cause the device to output a nonzero acceleration. To give
the user a more stable region around the zero point, we quantized all outputs below a
certain level to 0, then normalized any outputs out of this cutoff range by the breadth of
the cutoff range. For example, if the cutoff were abs(10), the intersection of all numbers >
-10 and all numbers < 10 defined the cutoff region, and any outputs outside of this range
would be normalized by +10 or -10, depending on whether the output were negative or
positive, respectively.
Hardware Design
We used the MMA7260QT accelerometer from Freescale Semiconductors. It is a low
cost capacitive micromachined accelerometer features signal conditioning, a 1-pole low
pass filter, temperature compensation and g-Select which allows for the selection among
4 sensitivities. Zero-g offset full scale span and filter cut-off are factory set and require no
external devices. Includes a Sleep Mode that makes it ideal for handheld battery powered
electronics.