THEORY OF OPERATION
For the following discussion, reference the lower
PC
board assembly schematic. Since
both
X
and
Y
circuit operation is identical, refer to the
X
circuit for this description.
The CX53 Trakball is
a
2-channel
D
to
A
converter which translates optically coupled
clocks into analog currents. The current sources or sinks into the two paddle line
inputs used for X-Y control in the 5200. Figure 7-3 is
a
function block diagram to
illustrate the following information.
When the cue ball is spun, the two roller shafts rotate.
Each shaft has
a
slotted
encoding wheel
at
one end which interrupts the two light sources in the optocoupler
for that channel. This produces
a
pair of alternating voltage wave forms from the
photo-transistors in the optocoupler (U2).
Comparator
A1
straightens the signals from
U1
into
5V
square waves and feeds them
to
A2
and A5.
These two clock waveforms are approximately 900 out of phase. This
allows correct direction sensing, depending upon which clock leads the other.
A2
senses which leading edge of the two clocks is coming first, thus determining
direction.
A5
combines the two clocks into one with doubled frequency, thus
increasing resolution. This clock is in turn fed into
A3
which sets the clock's pulse
width
at
a
constant duration while still allowing the frequency to vary with speed.
The
Q
and
Q
outputs from A2 are used to gate the fixed-width pulses from
A3
with the
directional clockgates
(Ah).
This produces alternating outputs depending upon
direction (Left or Right). The current integrator networks on the outputs of
A4A
&C
and
A5BK
then link these gated clocks to the analog input of the 5200 main console.
TP9
dr
TPlO each should have
a
ramp waveform approximately 3 volts in amplitude.
This
ramp waveform is generated in the
main
circuitry of the 5200 and is controlled by
increases or decreases
in
current caused by the Trakball circuit. When the ball is
stationary, the ramp will remain
at
approximately 3V. When the ball
is
spun in the
"right" or "down" direction an inverted clock siphons current off the corresponding
ramp with a net reduction in the slope of the ramp (-600mV max.
@
C7
and
C8).
When
the ball is spun in the "left" or "up" direction
a
positive clock causes positive current
integration, with
a
net increase
in
the slope of the ramp (+900mV max.
@C7
and C8).
The clear line (used for calibration) is held
HIGH
for normal operation. During
initialization the console pulls it
LOW.
This prevents any ball-generated clocks
coming from
A3,
and allows the
static
output level to
be
read and used
as
a
reference
reading
in
determining velocity change.
CX5200
Field Service Manual
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