Puff The Magic Mouse

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PuffThe Magic Mouse
BME 264 Medical Devices Dr. Patrick Wolf
April 22,

• Arthur Wood
• Jeff Keeney

2004
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Background and Objective

• Computers are ubiquitous in modern society
• Interface can be difficult for people with
  disabilities
• Keyboard and mouse require high level of
  dexterity
• - Objective create an interface that does not
  require complex movement of arms or hands

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Could use voicebut why bother?

• - Voice II Interface is very slow time between
  successive inputs 1 second
• - Accurate recognition depends on distance from
  microphone, ambient noise
• - Parts and software very expensive Voice II
  kit cost 50.00, voice recognition software can
  cost several hundred dollars
• - Parts break randomly, online documentation is
  often completely useless!

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Pressure Transducer Interface

• - Interface consists of mpx5100GP pressure
  transducer, surgical tubing, and straw
• - Inexpensive, parts easily replaced
• - PIC polls input pin for voltage jump
• - Looks for various combinations of long and
  short puffs

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Input Circuit and Block Diagram
Data
Pressure Input (Puff)
PIC
PC
mpx5100GP
Clock
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Software/Interface description

• - PIC polls input pin for high voltage using bit
  test
• - Program calls a delay function
• - Within the delay function are an additional
  series of bit tests and delays
• - Depending on when the bit tests within the
  first delay find a high voltage, puff is treated
  as short or long

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Puff Command Summary
Clock Mode Cycles Through Clock Positions 1 - 8
Grid Mode Cycles Through Locations 1 - 9
L
S
S
S

• Still Cursor

S Short Puff L Long Puff
S
Move
L,
S
Returns After Command
Click Mode Mouse Vibrates as indicator
Any Input
S
S,L
L
S,S
Single
Drag
Right
Double
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PS/2 Physical Interface
6-pin Mini-DIN (PS/2) Pin 1 Data Pin 2 Not
Implemented Pin 3 Ground Pin 4 Vcc (5V) Pin
5 Clock Pin 6 Not Implemented
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PS/2 Electrical Interface
PS/2 Electrical Interface
Data and Clock lines are both connected directly
from the computer to the PIC Both lines are
normally held at 5V, but either can be pulled
low by the computer Clock cycling always
performed by mouse
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PS/2 Communication Interface
Computer to Mouse

• Data high, Clock high Idle state.
• Data high, Clock low Communication
  Inhibited.
• Data low, Clock high Host Request-to-Send

Mouse to Computer

• Mouse-to-Computer The Data line changes state
  when Clock is high and that data is valid when
  Clock is low.
• Computer-to-Mouse Data line changes state when
  Clock is low, with exception of ACK

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PS/2 Movement Data Packet
L,R,0 Left, Right, Middle ButtonsXS,YS Sign
Bit of X and YXY,YY Overflow bit for X and
YX0-X7 Movement in X DirectionY0-Y7
Movement in Y Direction
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PS/2 Command Data Packet

• - Commands are sent by computer to mouse and
  consist of 2 bytes
• - Commands sent using request to send protocol
  and are largely used for handshaking and
  initialization
• After request to send, data is clocked in by
  mouse
• Using the PIC to control the clock allows for
  free transmission of data between device and host

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Acknowledgements

• - Dr. Patrick Wolf for taking the time to
  organize and teach the course
• - Michael Rizk for his infinite patience (even
  until 130am the night before) and for having the
  magic touch
• - Sensory Inc. for making a non-functional and
  poorly documented product that caused us to
  abandon our original scheme 12 hours before the
  deadline and devise a more efficient interface

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Any Questions?