The timing
functions
available
take
some
explaining
to
understand
how
they
differ from
each
other. Let
us take
a function
-by-
function
look
at them.
In function
1,
the
stopwatch
is
used
as
a start/stop
elapsed
time
indicator.
It
can
be used
to
time
any
one
or more
events,
displaying
the
time
it takes
for
each
successive
event
to
complete
while
counting
the
total
elapsed time
of
all events
separately.
Only the
par-
ticular
event
being
timed
is normally
displayed.
Then
you
press
a button
to
display
the total
elapsed,
excluding
any times
out or
delays
between
events.
This
mode is
excellent
for
tim-
ing periods
in
basketball
games.
In
function
2,
the
stopwatch
be-
comes
a
sequential
timer. This
lets
you
time
each part
of a given
continuous
event,
such
as separate
lap
times in
an
auto
race
or the
times
between hand
-
offs
in
relay
footraces.
Meanwhile,
the
stopwatch
times
the
period
of the
overall
event.
Function
3 is for
total
activity
timing.
This
function
is
similar to
the first,
dis-
playing
the
elapsed
time
fora
series
of
events,
minus
times
out
between
events.
Where
it
differs
is that,
with the
press
of a
button, you
can
also
display
total
elapsed
time,
including
the
times
out.
In
function
4,
the
stopwatch
oper-
ates in
a
split mode.
The
display
gives
the
cumulative
time
to
each "split"
point in
an event
while
timing
the
overall
event
separately.
Setting
the
function
switch
to posi-
tion
5
sets the
stopwatch
up as
a stop/
start activity
timer.
In
this mode,
the
stopwatch gives
separate
times for
each
event
as well
as the
total time
of
all events.
Functions
6 and 7
are unique.
They
let
you
count up to
or down
from
a
preprogrammed
time,
respectively,
over a
9
hour,
59
minute,
59.99
second
range.
To
operate
in these
modes,
the
display
must
be set to the reference
time
by first
operating the
RESET
switch to display
all
zeros.
Then the
function
switch
is
set to
each of posi-
tions 1 through
5 and simultaneously
with
the pressing
of the
S/S (start/stop)
and
F/S (final stop)
switches located
on
the left
and right
of the case.
Once the
reference
time is
established
on the
display,
you
switch
back to
function
6
to
operate the
RESET /(LOAD)
switch to
program
the internal
counter.
After
loading
the
program,
you
either
stay
in function
6 to
count up
from
zero
to the reference
time
or
switch to function
7 to
count
down
from
the
reference
time to
zero
by
pressing
the
S/S switch. When
the
stopwatch
completes
the
counting
cycle,
all counting
stops. If
a signalling
device is
plugged into
the
alarm jack
at the top
of the
case, an
alarm will
sound at the
termination
of the
count.
(The
kit's
assembly manual
provides
full
details
for
connecting
various
types
of alarm
devices.)
There
are two more
jacks
on
the
top
of
the
case. One is for plugging
in the
battery
charger /eliminator,
and the
other is
for operating
the
start/stop
function
remotely
(either
manually
or
by automatic
trip devices). The
start/
stop jack is
wired in parallel
with the
S/S switch.
Two
PMOS
LSI
chips are
used in-
side the
stopwatch for
all counting
operations.
A quartz
crystal provides
an accurate,
stable time
-base refer-
ence.
About
the
Kit.
The
stopwatch ranks
as a
one -evening kit
project for
the
experienced
kit
builder. Even
a new-
comer
can assemble
and
start using
the
stopwatch in little more
than
seven
or eight
hours.
This
is
possible
be-
cause
all of the
complex circuits
are
contained
in the
two counter IC's.
There
are very few
discrete
compo-
nents
to
be wired to
the two
screened,
double
-sided printed-
circuit
boards.
The
LED
displays
come in
lensed
DIP
cases,
and they
and the IC's
plug
into
sockets.
This
eliminates
the
pos-
sibility
of heat
damage
during
solder-
ing
and makes it
easy to troubleshoot
and replace
defective
components
should
the need
arise.
There
are no
critical
steps to
per-
form
during
assembly.
However,
be-
cause the
LSI
chips
are MOS
devices,
safe
-handling
precautions
must
be
exercised
(see
assembly
manual).
User
Comment.
Heath
claims
an
accuracy
of ±0.006%
when the
stop-
watch is
adjusted
without
instruments
and
better than
-*0.003%
with instru-
ments.
We
tried
both ways
and
ob-
tained
better than ±0.003%
in
both
cases. Just
as
important,
the long-
and
short-term
stabilities
were
excellent.
We used
a 15- minute
short -term test
and
observed no
significant
drift. At
the
end
of a
25
-hour (long -term)
test,
operating the
stopwatch
on the bat-
tery
charger /eliminator,
we
observed
a
difference
of
4.31
seconds when
corn -
pared
against
a
WWV
calibrated
timer.
These
results
were
obtained with
the
stopwatch
aligned without
in-
struments.
After
aligning
with instru-
ments
and repeating
the
25
-hour test,
there
was
a discrepancy
of less than
1
second
between
the
stopwatch
and
reference
timer,
which
in
all
likelihood
was
due to reaction
time
lag
when
both were
started
and
stopped.
This
is
a very
easy
stopwatch
to use
and
operate.
With the
S/S and
F/S but-
tons
located
on either
side of the
dis-
play, it
is not limited
to
either right-
or
left-
handed
operation. Also,
the
grasp
is
comfortable.
A nice final
touch is the
sun shield,
especially
useful when
reading
the LED
display
under high
ambient lighting
conditions.
CIRCLE NO. 90 ON FREE INFORMATION
CARD
TRI -STAR
"TIGER SST"
CD
IGNITION
SYSTEM
Capacitive
-discharge kit
system
for autos.
MANY
different
circuits
have
been
designed
to
increase
the
per-
formance
of automotive
engines by
upgrading
the ignition
system.
One of
these
is the
capacitive-
discharge sys-
tern (CDI)
which
boosts
the voltage
applied
to the primary
of
the ignition
coil.
The
Tri -Star "Tiger
SST"
is
such
a
CDI circuit. It is triggered
by the exist-
ing
breaker points
and
is
fully compat-
ible
with
stock as well as "breaker -
less" ignition
systems.
78
The
Tiger
SST is
available tactory-
wired for $42.95
and in
Simpli -Kit form
for $31.95.
General Description. The ignition
system utilizes
a two -transistor multi -
vibrator
whose
operating frequency
is
set at about
8000
Hz.
This frequency is
high
enough to prevent
the
syn-
chronization problems
that
plagued
earlier
CDI system
designs.
The multivibrator
converts the 12-
volt vehicle
electrical
system
potential
to
a square
-wave ac
signal. A trans-
former
then
steps up this
signal
and
passes it to
a
full -wave
rectifier
-diode
bridge to
convert it to
pulsating
dc.
Following
the
bridge
is
a 2.2 -µF
stor-
age capacitor that
begins to
charge up
from the
bridge's
output signal.
A
signal
from
the vehicle's
breaker
points
triggers an
SCR
in the
CDI sys-
tern. This
permits
the
storage
capacitor to discharge
its
stored
400
POPULAR ELECTRONICS
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