Msg: 7053 *Conference*

04-03-97 16:25:16

From: RON WIESEN

To : TOM UPTON

Subj: REPLY TO MSG #7048 (NAYBOR.BA)

What Comet means is there's only one input line from the Wand port.  For mouse
movement, 2-axis input is needed - if there are mouse "buttons" then they are
additional input requirements.  Considering 2-axis motion input, and ignoring
"buttons", there's a conventional solution and a comprimised unconventional
solution.

You're interrupted light beam is closer to the unconventional solution Tom.
First, the conventional solution: use the Wand input as one axis and SOME OTHER
INPUT for the second axis. The Cassette port has an input - bet you're not
using a cassette recorder. So the cable "tail of the mouse" splits to two
connectors (Wand and Cassette) - no biggie.

For unconventional solutions that have only PHYSICAL INPUT PORT, modulation can
multiplex more than one signal onto one physical input. The Cassette port in
fact demodulates to two signals (1 and 0), but they are mutually exclusive so
it's just commutation. You prefer (need?) simultaneous demodulation to two
signals.  Modems above 600 Baud do this.  For example, at 2400 bits per second
transmission rate the "carrier" changes at only 600 Baud and each change
represents one of 4 possible "bit pairs". So in one second of time, 600 changes
of the carrier expresses 2400 bits of transmission.  The 300 bit per second
transmission of the Modem in the Model 100 isn't like this - it's carrier
changes at 300 Baud but each change expresses just "one bit" so transmission
rate is 300 bit per second.

Here's an unconventional solution using the Wand port.  The Wand port supplies
+5 volt continuously at a modest power - enough power for a "mouse modulator"
circuit.  Make a circuit that multiplexes the forward/backward and left/right
positional information onto the Wand input port.  There's a comprimise because
no circuitry is changed inside the Model 100 - a software driver discriminates
the signal of the Wand input port to derive "TWO SIMULTANEOUS AXIS POSITIONS"
of the mouse.  There's several ways to do it - here's one.

Left/Right presents 1 of 3 possible states: motion left, no motion, or motion
right.  Likewise Forward/Backward has 3 states: motion forward, no motion, or
motion backward.  The circuit has a 3-frequency oscillator controlled by
Left/Right state, which feeds a 3-mode octave generator controlled by
Forward/Backward state.  The circuit produces 1 of 9 frequencies which the
software samples and discriminates.  For simple electronics, the modes of the
octave generator are:

1.  half frequency 2.  same frequency (it passes through unaltered) 3.  double
frequency

For easy discrimination by the software, choose the 3 frequencies of the
oscillator so they:

o   all lay within the same octave scale (highest/lowest is less than 2) o
avoid "paired" relationships of equal difference

I'll leave the choice of 3 frequencies (f1, f2, and f3) for you to investigate.
Choose them for easy discrimination among the 9 results.  The results are:

f1/2  Left & Forward f1    Left f1*2  Left & Backward f2/2  Forward f2    no
motion f2*2  Backward f3/2  Right & Forward f3    Right f3*2  Right & Backward