Specifications
CIRCUIT IDEAS
lector and emitter of the in-built transis-
tor) is connected to the two terminals of
the ‘=’ (of Casio FX-82LB used during actu-
al testing at EFY) button’s keypad tracks,
with collector connected to the more posi-
tive terminal than the emitter. Thus, once
every second the ‘=’ button is activated.
To operate the calculator in stopwatch
mode, switch on the calculator and press
the keys in the following sequences:
(a) For seconds mode: [1][+][+]
(b) For minutes mode: [6][0][1/x][+][+]
(c) For hours mode: [3][6][0][0][1/x][+][+]
Note: The invoking of function (1/x)
in different calculators may require press-
ing of a function key marked ‘INV’ or
‘SHIFT’ or ‘2ndF’, etc. Hence, use the ap-
propriate key in your calculator for 1/x
operation.
For accurate starting, press the ‘0’ key
to reset the count immediately after press-
ing the start switch. (However, if you de-
sire upcounting from a number other than
‘0’ second/minute/hour in respective modes,
you may do so by keying that number im-
mediately after pressing start switch.) The
final reading can be taken by pressing the
stop switch. The fractional portion of the
results obtained during minutes mode and
hours mode can be converted to sexagesi-
mal notation (i.e. degree, minute, second)
by invoking ‘
° ' '' ’ key. For example, a di-
splay of 5.87 in hour mode will get conver-
ted to 5, 52,12 (5 hrs, 52 min., and 12 sec.)
when one invokes ‘
° ' '' ’ function key.
For downcounting in seconds, min-
utes, or hours mode, the procedure as out-
lined in the preceding paragraphs is to be
followed except that keys [-][-] should be
depressed in place of [+][+].
Pause/hold can be achieved by press-
ing the ‘=’ key continuously, or pressing
switch S2. Intermediate time can be stored
by pressing the ‘Min’ key. This reading
can be retrieved by pressing the ‘MR’ key,
after the stop switch has been pressed.
This circuit can easily be installed in-
side the calculator. There is a vacant space
of 60x22x6 mm inside the Casio FX-82B
calculator. By using a chip LED, the size
restriction for installing the LED can be
overcome. It can be placed near the LCD
display to provide indication of the func-
tioning of the stopwatch. The whole cir-
cuit can be assembled on a 55x20 mm
PCB. The start/stop tactile switches can
also be installed inside, with their operat-
ing lever popping out through a cutout
above the keypad.
You may find certain keypad buttons
such as ‘hyp’ which you may never re-
quire to use. Two such buttons can be
removed to create place for ‘start’ and ‘stop’
switches, if required. By this arrangement,
you can start or stop the clock, without
affecting its working.
vides precision DC voltages from 0 to 10
volts, in steps of 0.01V, can be easily and
economically built using a circular volt-
age divider. In this simple divider arrange-
ment, the points across which the output
is taken remain fixed, while the voltage
source is moved from one pair of points
to another.
As shown in the diagram, a total of
31 resistors are required to provide
settability to within 0.01V. There are a
total of three such dials. Each dial has
ten resistors, except the last one (dial III),
which contains eleven resistors. Dial 1
has ten resistors, having a value of 1 kilo-
ohm each. It is marked from 0 to 9 volts
RUPANJANA
RATHINDRA NATH BISWAS
I
n a conventional voltage-divider set-
up, the fixed voltage is applied across
the entire network and the output
is taken from across a selectable tap. Al-
though this approach provides precision
voltage out-
put, it in-
volves com-
plex switch-
ing and un-
usually
large num-
ber of resis-
tors. Thus, it
is not eco-
nomical, as
precision re-
sistors are
quite expen-
sive.
A bridge
that pro-
DIAL A VOLTAGE
114