sf
m
cos
o
o
r
y
After
the
signals
are
ampli ed
in
an
A
GC
ampli er using
the
demo
dulated
sum
as
a
reference
and
brough
t
to
baseband
b
y
the
demo
dulator
this
computation
is
done
using
t
w
o
simple
opamp
circuits
that
are
then
fed
in
to
a
m
ultiplier
circuit
con gured
as
a
divider
The
phototransistors
are
used
to
trigger
a
ramp
circuit
used
as
an
analog
timing
reference
for
in
terp
olating
the
mirror
angle
b
et
w
een
the
start
and
stop
pulses
The
ramp
is
built
out
of
a
phase lo
c
k
ed lo
op
lo
c
k
ed
to
the
motor
sp
eed
This
allo
ws
the
unit
to
main
tain
a
con
tin
uous
measuremen
t
of
angle
indep
enden
t
of
a
v
erage
motor
sp
eed
The
ramp
signal
along
with
the
range
signal
is
sen
t
to
the
micro
con
troller
b
oard
An
image
of
the
circuit
b
oards
app
ears
in
Fig
Data
Acquisition
and
Analysis
A
data
acquisition
b
oard
based
around
the
Motorola
HC
micro
con
troller
is
used
to
in
terface
the
range nder
to
the
host
computer
It
p
erforms
limited
data
analysis
and
reduction
Figure
sho
ws
this
system
in
op
eration
trac
king
a
hand
across
a
scanned
tabletop
Ho
w
ev
er
this
system
w
as
nev
er
used
with
a
more
sophisticated
program
as
it
didn t
pro
vide
enough
range
for
the
in
tended
application
The
use
able
range
w
as
less
than
one
meter
The
asymptotic
fallo
with
r
see
eq
sev
erely
limited
the
dynamic
range
of
the
system
This
opted
for
dev
eloping
the
phase measuremen
t
device
Con
tin
uous
W
a
v
e
Phase
A
con
tin
uous w
a
v
e
CW
phase measuring
range nder
w
as
constructed SP
Tw
o
v
ersions
w
ere
built
a
protot
yp
e
and
more
robust
v
ersion
for
public
installations
F
or
the
purp
ose
of
the
design
w
e
shall
describ
e
the
second
b
etter p
erfected
v
ersion
The
circuits
w
ere
similar
in
b
oth
cases
The
ma
jor
c
hanges
w
ere
mostly
in
data
acqui
sition
and
soft
w
are
Both
devices
w
ere
displa
y
ed
in
ternally
at
the
Media
Lab
The
second
device
w
as
sho
wn
with
a
public
installation
at
SIGGRAPH
SRP
The