Specifications

CIRCUIT IDEAS
T
he latch-up alarm described here
is based on single IC NE555,
configured as an astable
multivibrator. The timing components are
selected such that the oscillation fre-
quency of the multivibrator lies within
the audio range. Instead of a flip-flop
stage, an opto-coupler (MCT2E) is used
for latching of the alarm.
Under normal condition, pin 4 of IC1
is pulled to ground via resistor R2, and
its output at pin 3 is held ‘low’. When
switch S1 is pressed momentarily, tran-
sistor T1 conducts to bring reset pin 4 of
555 to logic ‘high’. As a result, IC1 is
activated and the alarm starts to sound.
LATCH-UP ALARM
USING OPTO-COUPLER
PRADEEP G.
S.C. DWIVEDI
Simultaneously, the LED inside opto-
coupler glows and the phototransistor
conducts. As a result, trigger transistor
T1 gets base bias via phototransistor and
resistor R6. The alarm sounds
continuously until reset switch S2 is
pressed. When switch S2 is pressed, tran-
sistor T1 is switched ‘off’ to bring pin 4
of IC1 to logic ‘low’ and the alarm
is disabled.
S.C. DWIVEDI
T
he UM5506B is a highly integrated
voice processor CMOS IC with in-
built ADM (adaptive delta modu-
lation) capability. The chip integrates an
analogue comparator, a 10-bit D/A con-
verter, a low-pass filter, an op-amp, and
a 96-kilobit static RAM. It has an on-chip
amplifier for sound recording and direct
speaker driving capability.
Although 28 pins/pads are shown
in the figure, its COB version mounted
on a PCB, as tested at EFY Lab, had only
16 lines coming out of the COB. These
lines, after proper identification, have
been indicated with asterisk (*) marks in
Fig. 2. Very few external components are
needed for its use in applications such as
greeting cards or toys. The tested PCB
measured 3 cm x 5.25 cm and required
only 3-volt supply for operation.
The IC, along with external compo-
nents, as shown in Fig. 2, can be used for
recording of sound for a recording length
of 6 seconds. During record mode, the
voice signals picked up by the condenser
mic are converted into digital signals us-
ing ADM algorithm and stored in its in-
ternal SRAM. During play mode, the digi-
tal data is converted back into analogue
signals and played back through the
speaker. For understanding the operation,
the functions of switches S1 through S4
and their corresponding pins is described
below.
S1(RECL). Pressing (grounding) this
pin ends the power-down mode and ini-
tiates a record cycle. Recording continues
as long as this pin is held ‘low’, provided
memory is not completely filled. If
memory is full or the pin is ‘high’, it en-
ters the power-down mode.
MINI VOICE-PROCESSOR
(BASED ON UMC APPLICATION NOTE AND
DATA SHEET FOR IC UM5506B)
69