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Disguise your voice
to sound like Darth
Vader from “Star
Wars” or a Cylon
from “Star Trek”.
With the added
menace of a new
strange-sounding
voice, you too can
travel the galaxy
for profit and
entertainment.
By JOHN CLARKE
e
c
i
o
V
r
e
d
Va
T
HE DARTH VADER and Cylon
characters have always had
great appeal, probably because
of their distinctive metallic voice
styles. This simple project lets you
imitate the dastardly Darth and other
diabolical characters from the nether
regions of the galaxy. All you do is
switch it on, speak into a small electret
microphone and adjust a single pot to
get the effect you want.
Now it’s quite possible that some
people might not see the need for
building such a handy space-war accessory as this. To others, the reasons
will be self-evident – after all, why
should you be forced to stick with your
own everyday boring voice?
As can be seen from the photos,
22 Silicon Chip
the Vader Voice is housed in a small
plastic case. The controls include an
effects rate adjustment (which varies
the type of sound), a volume control
to set the output level from the loudspeaker and an on/off switch. The
loudspeaker is mounted inside the
case while the microphone is located
in a small film canister connected via
a length of shielded cable.
How it works
Fig.1 shows the block diagram for
the Vader Voice. The action starts on
the lefthand side, where an electret
microphone feeds signal to an op amp
stage (IC1a) which has a gain of about
15. A chopper circuit (ie, CMOS switch
IC2) then switches the signal on and
off at a rate determined by oscillator
stage IC3 and potentiometer VR1.
The output from the chopper stage is
fed to a 3kHz low-pass filter based on
IC1b. This stage removes the residual
signals produced by the switching
action in IC2. Finally, IC4 feeds the
processed signal to power amplifier
stage IC4 via volume control VR2.
Fig.2 illustrates how the circuit
produces the sound ef
fects. Waveform A is the audio signal from the
microphone after passing through
amplifier IC1a, while waveform B is
the square wave output from the oscillator. Waveform C shows the audio
signal after it has been “chopped” at
the oscillator frequency.
The bottom waveform at D shows
the corresponding output from the
low-pass filter (IC1b). Note that this
waveform is quite different in appearance to the original waveform shown
at A and it sounds correspondingly
different too.
Refer now to Fig.3 for the complete
circuit. Apart from the microphone
and loudspeaker, it uses four lowcost ICs plus a few resistors and
capacitors.
The electret microphone requires
a bias in order to function. This is
supplied via a 10kΩ resistor which is
decoupled from the supply rail via a
1kΩ resistor and 33µF capacitor. This
decoupling arrangement is necessary
to prevent supply line fluc
tuations
caused by the power amplifier stage
from modulating the microphone and
causing positive feedback.
The signal from the electret microphone is fed via a .0033µF capacitor
to pin 3 of op amp IC1a. This stage is
connected as a non-inverting amplifier
with a gain of about 15, as set by the
470kΩ feedback resistor and the 33kΩ
resistor on pin 2 (ie, Gain = 1 + 470/33
= 15.2).
IC1a is biased at half the supply
voltage via two 220kΩ resistors and the
associated 470kΩ resistor connected to
pin 10. A 10µF electrolytic capacitor
decouples the half-supply voltage,
which is also used to bias pins 2 & 1
of IC2 and pin 5 of op amp IC1b. As
a result of this bias arrangement, the
output from IC1a swings above and
below +4.5V.
AMPLIFIER
x15.5
MICROPHONE
IC1a
3kHz LOW
PASS FILTER
IC1b
CHOPPER
IC2
A
C
POWER
AMPLIFIER
D
VOLUME
VR2
IC4
B
EFFECT
RATE
VR1
LOUDSPEAKER
OSCILLATOR
IC3
Fig.1 (above): block diagram of the
Vader Voice. The signal from the
microphone is amplified in IC1a and
“chopped” in IC2 at a rate set by
oscillator IC3. The resulting signal is
ten filtered in IC1b and fed to audio
amplifier stage IC4.
A
B
Fig.2 (right): this diagram shows
the effect on the input waveform at
various points in the circuit. Note
that the output waveform (D) is quite
different to the input waveform (A).
The oscillator stage is formed by IC3
which is a 7555 CMOS timer. This stage
generates a square wave output with
a frequency in the range from 1.3kHz
to 14kHz, depending on the setting of
VR1. Let’s see how it works.
At switch on, the 0.1µF timing
capacitor is initially dis
c harged
and the output at pin 3 is high. The
0.1µF capacitor then charges via the
1kΩ resistor and VR1 until it reaches
2/ Vcc (ie, 2/ the supply voltage).
3
3
When it does, pin 3 switches low
C
D
and the timing capacitor discharges
via the 1kΩ resistor and VR1 until it
reaches 1/3Vcc. This switches pin 3
high again and so the process is repeated indefinitely while ever power
is applied.
Fig.3 (below): the final circuit uses
7555 timer IC3 to drive CMOS switch
IC2 and this stage in turn chops the
audio waveform from IC1a. IC1b is
the 3kHz low-pass filter stage and this
drives IC4 via volume control VR2.
S1
1k
33
10k
0.1
220k
.0033
470k
MIC
220k
8
3
10
16VW
33k
2
IC1a
LM358
9V
IC2
4066
1
.0068
14
2
13
470k
470k
1
7
10k
.012
22k
10k
.01
.001
10k
6
5
4
470k
7
IC1b
VOLUME
VR2
10k LOG
RATE
VR1
10k LIN
+9V
4
1k
6
8
3
6
5
IC4
2 LM386
4 .047
100
16VW
8W
10
0.1
3
IC3
7555
2
100
16VW
0.18
1
VADER VOICE
0.1
September 1995 23
1
100uF
33k
470k
220k
220k
IC2
4066
.01
.012
C
❏
❏
❏
❏
❏
❏
❏
❏
❏
9V
BATTERY
AND CLIP
1 .0033
.047
TABLE 2: CAPACITOR CODES
10uF
IC1
LM358
0.1
IC3
7555
0.1
0.1
1
D
.0068
470k
A
470k
B
1k
100uF
S1
10k
IEC Code
180n
100n
47n
12n
10n
6n8
3n3
1n0
EIA Code
184
104
473
123
103
682
332
102
10k
0.18
1
1k
22k
10k
470k
10
IC4
LM386
10k
Value
0.18µF
0.1µF
.047µF
.012µF
.01µF
.0068µF
.0033µF
.001µF
.001
33uF
C
the output each time the potentiometer
was operated.
Following VR2, the signal is coupled to pin 3 of IC4, an LM386 audio
amplifier which is capable of driving
an 8Ω loudspeaker at an output power of up to 1W. Its output appears at
pin 5 and drives the loudspeaker via
a 100µF capacitor which rolls off the
response below about 200Hz. In addition, a Zobel network consisting of
a .047µF capacitor and a 10Ω resistor
is connected across the output of IC4
to prevent high frequency instability.
Power for the circuit comes from a
9V battery and is applied via on/off
switch S1. A 100µF electrolytic capac
itor provides supply line decoupling,
to minimise variations due to the peak
currents through the LM386 audio
amplifier.
D
VR2
A
B
SPEAKER
VR1
MICROPHONE
Fig.4: install the parts on the PC board and complete the wiring as shown in
this diagram. Note that shielded cable is used for the connections to volume
control VR2 and to the electret microphone.
The square wave output at pin 3 of
IC3 toggles CMOS analog switch IC2 on
and off. When pin 3 of IC3 is high, the
CMOS switch is closed. Conversely,
when pin 3 is low, the CMOS switch
is open. As a result, the signal from
IC1a is gated at the oscillator frequency
before it is fed to IC1b.
IC1b and its associated resistors
and capacitors form the third order
Construction
low-pass filter. This rolls off the signal above 3kHz at 60dB per decade
(ie, 20dB/octave). This means that
at 30kHz the signal is attenuated by
60dB.
The filtered signal appears at pin 7
of IC1b and is AC-coupled via a 0.18µF
capacitor to volume control VR2. This
AC coupling prevents DC from flowing
in VR2, which would cause noise in
A PC board coded 08310951 carries
most of the parts for the prototype.
This board was housed in a plastic case
measuring 130 x 67 x 43mm, while a
self-adhesive label was designed for
the front panel.
Fig.4 shows the wiring details. Start
the PC board assembly by installing PC
stakes at all external wiring points and
at the S1 position. This done, install
TABLE 1: RESISTOR COLOUR CODES
❏
❏
❏
❏
❏
❏
❏
❏
No.
4
2
1
1
4
2
1
24 Silicon Chip
Value
470kΩ
220kΩ
33kΩ
22kΩ
10kΩ
1kΩ
10Ω
4-Band Code (1%)
yellow violet yellow brown
red red yellow brown
orange orange orange brown
red red orange brown
brown black orange brown
brown black red brown
brown black black brown
5-Band Code (1%)
yellow violet black orange brown
red red black orange brown
orange orange black red brown
red red black red brown
brown black black red brown
brown black black brown brown
brown black black gold brown
PARTS LIST
1 PC board, code 08310951, 82
x 62mm
1 plastic case, 130 x 67 x 43mm
1 front panel label, 62 x 212mm
2 knobs
1 SPDT toggle switch (S1)
1 57mm diameter 8-ohm
loudspeaker
1 9V battery clip
1 9V battery
12 PC stakes
1 electret microphone insert
1 16mm 10kΩ linear pot (VR1)
1 16mm 10kΩ log pot (VR2)
1 800mm-length of shielded
cable
1 80mm-length of twin speaker
wire
1 200mm-length of hookup wire
1 20mm-length of 0.8mm tinned
copper wire
Semiconductors
1 LM358N dual op amp (IC1)
1 4066B quad analog switch
(IC2)
1 7555 CMOS timer (IC3)
1 LM386N audio amplifier (IC4)
The PC board was secured by clipping it into slots that run along either side of
the case, while the loudspeaker was fastened to the lid using contact adhesive.
Make sure that the battery clip is correctly wired to the board.
the wire link adjacent to IC2, then
install the resistors and capacitors.
Tables 1 & 2 show the resistor and
capacitors codes but it is also a good
idea to check the resistor values using
a multimeter, as some colours can be
difficult to read.
Take care to ensure that the four
electrolytic capacitors are correctly
oriented. In particular, note that the
two 100µF capacitors are oriented in
opposite directions.
The three ICs can now be installed,
again taking care to ensure that they
are all correctly oriented. It is quite
easy to identify pin 1 of an IC, as it is
always adjacent to a dot or notch in
one end of the IC’s body (see Fig.4). Be
careful not to get the 8-pin ICs mixed
up and don’t use a conventional 555
timer for IC3. It must be a CMOS 7555
type to ensure low battery drain.
Switch S1 is mounted on top of the
PC stakes, to give it sufficient height
to later protrude through the front
panel. When the PC board has been
completed, it can be clipped into the
case as shown in the photo.
Next, affix the adhesive label to the
lid of the case and use it as a template
for drilling the holes. You will have to
drill holes for the Volume and Effect
pots, the Power switch and the loudspeaker grille. A small hole is also
required in one end of the case for the
microphone lead.
Take care when mounting the two
pots on the lid. VR1 (Effects) is a 10kΩ
linear type, while VR2 (Volume) is
a 10kΩ log type. The loudspeaker is
mounted using contact adhesive.
Once everything is in position, the
wiring can be completed as shown in
Fig.4. Light-duty figure-8 cable is used
Capacitors
2 100µF 16VW PC electrolytic
1 33µF 16VW PC electrolytic
1 10µF 16VW PC electrolytic
1 0.18µF MKT polyester
3 0.1µF MKT polyester
1 .047µF MKT polyester
1 .012µF MKT polyester
1 .01µF MKT polyester
1 .0068µF MKT polyester
1 .0033µF MKT polyester
1 .001µF MKT polyester
Resistors (0.25W, 1%)
4 470kΩ
4 10kΩ
2 220kΩ
2 1kΩ
1 33kΩ
1 10Ω
1 22kΩ
Miscellaneous
Plastic 35mm film canister, epoxy
resin, solder
for the loudspeaker connections and
for wiring the Effects pot, while shielded cable must be used for the Volume
control wiring. The battery clip can
also be wired in at this stage –be sure
to connect the red lead to the positive
terminal on the PC board.
Shielded cable must also be used
September 1995 25
Fig.5: this is the
full-size etching
pattern for the
PC board. Check
your board
carefully before
installing any
parts.
for the microphone lead. Use a length
of about 600mm and feed it through
the end of the case before soldering
it to the PC board terminals. The
microphone itself can be mounted in
a plastic film canister or some other
similar plastic container.
In the prototype, the microphone
was mounted through a hole drilled in
the cap of the film canister and secured
with a dab of epoxy. The lead passes
through a second hole drilled in the
bottom of the canister.
Finally, the battery can be clipped
into position and the lid attached.
Testing
To test the project, simply switch
it on, wind the volume control up
and speak into the microphone. You
should immediately be rewarded with
a metallic sounding voice. Adjust the
Effects pot (VR1) until you obtain the
sound you want. All you need now is
a helmet, a black cloak, a breathing
mask and a light stick to terrorise the
galaxy, or just the immediate neighbourhood.
If Darth doesn’t do his stuff, first
check that each com
ponent is in
its correct location and that all polarised parts are correctly oriented.
You should also carefully check the
underside of the PC board for solder
bridges or missed (or bad) solder
connections.
Next, check for +9V on pin 8 of IC1,
pin 14 of IC2, pins 4 & 8 of IC3 and pin
6 of IC4. Pins 2 & 5 of IC1 should be
at +4.5V, as should pins 1 & 2 of IC2.
Check the relevant circuit components
carefully if you do encounter any incorrect voltages.
If all you get is your normal amplified voice, check that oscillator IC3
is working correctly. It should have
an average voltage of 4.5V at pin 3,
as measured on a multimeter. If you
don’t get any sound at all, try bridging
pins 2 & 1 on IC2. This will tell you
whether or not CMOS switch IC2 is
functioning, or whether the fault lies
elsewhere in the circuit.
SC
ANOTHER GREAT DEAL FROM MACSERVICE
100MHz Tektronix 465M Oscilloscope
2-Channel, Delayed Timebase
VERTICAL SYSTEM
Bandwidth & Rise Time: DC to 100MHz (-3dB) and 3.5ns or
less for DC coupling and -15°C to +55°C.
Bandwidth Limit Mode: Bandwidth limited to 20MHz.
Deflection Factor: 5mV/div to 5V/div in 10 steps (1-2-5 sequence). DC accuracy: ±2% 0-40°C; ±3% -15-0°C, 40-55°C.
Uncalibrated, continuously variable between settings, and to
at least 12.5V/div.
Common-Mode Rejection Ratio: 25:1 to 10MHz; 10:1 from
10-50MHz, 6cm sinewave. (ADD Mode with Ch 2 inverted.)
Display Modes: Ch 1, Ch 2 (normal or inverted), alternate,
chopped (250kHz rate), added, X-Y.
Input R and C: 1MΩ ±2%; approx 20pF.
Max Input Voltage: DC or AC coupled ±250VDC + peak AC at
50kHz, derated above 50KHz.
HORIZONTAL DEFLECTION
Timebase A: 0.5s/div to 0.05µs/div in 22 steps (1-2-5
sequence). X10 mag extends fastest sweep rate to 5ns/div.
Timebase B: 50ms/div to 0.05µs/div in 19 steps (1-2-5 sequence). X10 mag extends maximum sweep rate to 5ns/div.
Horizontal Display Modes: A, A Intensified by B, B delayed
by A, and mixed.
CALIBRATED SWEEP DELAY
Calibrated Delay Time: Continuous from 0.1µs to at least 5s
after the start of the delaying A sweep.
Differential Time Measurement Accuracy: for measurements
of two or more major dial divisions: +15°C to +35°C 1% + 0.1%
of full scale; 0°C to +55°C additional 1% allowed.
TRIGGERING A & B
A Trigger Modes: Normal Sweep is triggered by an internal
vertical amplifier signal, external signal, or internal power line
signal. A bright baseline is provided only in presence of trigger
signal. Automatic: a bright baseline is displayed in the absence
of input signals. Triggering is the same as normal-mode above
40Hz. Single (main time base only). The sweep occurs once
with the same triggering as normal. The capability to re-arm
the sweep and illuminate the reset lamp is provided. The sweep
activates when the next trigger is applied for rearming.
A Trigger Holdoff: Increases A sweep holdoff time to at least
10X the TIME/DIV settings, except at 0.2s and 0.5s.
Trigger View: View external and internal trigger signals; Ext
X1, 100mV/div, Ext -: 10, 1V/div.
Level and Slope: Internal, permits triggering at any point on
the positive or negative slopes of the displayed waveform.
External, permits continuously variable triggering on any level
between +1.0V and -1.0V on either slope of the trigger signal.
A Sources: Ch 1, Ch 2, NORM (all display modes triggered by
the combined waveforms from Ch 1 and 2), LINE, EXT, EXT
:-10. B Sources: B starts after delay time; Ch 1, Ch 2, NORM,
EXT, EXT :-10.
Optional cover for
CRT screen – $35
through the vertical system. Continuously variable between
steps and to at least 12.5V/div.
X Axis Bandwidth: DC to at least 4MHz; Y Axis Bandwidth:
DC to 100MHz; X-Y Phase: Less than 3° from DC to 50kHz.
DISPLAY
CRT: 5-inch, rectangular tube; 8 x 10cm display; P31 phosphor. Graticule: Internal, non-parallax; illuminated. 8 x 10cm
markings with horizontal and vertical centerlines further marked
in 0.2cm increments. 10% and 90%
for rise time measurements.
Australia’s Largest Remarketer of markings
Graticule Illumination: variable. Beam
Test & Measurement Equipment
Finder: Limits the display to within the
graticule area and provides a visible
9500; Fax: (03) 9562 9590
display when pushed.
X-Y OPERATION
Sensitivity: 5mV/div to 5V/div in 10 steps (1-2-5 sequence)
MACSERVICE PTY LTD
20 Fulton Street, Oakleigh Sth, Vic., 3167. Tel: (03) 9562
**Illustrations are representative only. Products listed are refurbished unless otherwise stated.
26 Silicon Chip
$900
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