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Project by Phil Prosser
The Styloclone
musical instrument
This reinvention and homage to a musical classic is an excellent project for
starters. It’s also lots of fun for the musically inclined, especially those interested
in old-school instruments. The whole project fits on one easy-to-build circuit board
that can be mounted in a case or built as a free-standing project!
T
his project is simple enough to be
ideal for people learning electronics,
but useful enough to be fun for all ages.
A Stylophone is a very simple musical
instrument that can play a single note
at a time, driven by a stylus (or pen).
A unique feature of a Stylophone is
that it uses tracks on the PCB to form
the instrument’s keys.
The original Dubreq Stylophone was
released in 1968. While it has never
become as popular as, say, the electric guitar, it definitely made a mark
on popular music! Notable uses of a
Stylophone are at the start of David
Bowie’s “Space Oddity” and throughout the Tornados’ instrumental, “Telstar”. So, while simple, the distinctive
sound of this instrument has a real
place in music.
The name “Styloclone” indicates
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it is not a real Stylophone; it is more
an homage to the original instrument,
drawing inspiration from it. Our
version draws a lot from the 1970s
design of the Stylophone, and keeps
the essentials such as the PCB tracks
forming the keyboard.
As an engineer, my immediate reaction to this project was to ‘gold plate’
it, allowing it to do things that no sensible person would want. However,
that would miss the essence of the
Stylophone.
We could have based it on a microcontroller, allowing all manner of
clever stuff, including fancy waveforms and effects. Alternatively, we
could ‘keep the purity’, as local Sydney musician Blair “Moog” Joscelyne
would say (www.blairjoscelyne.com).
[He is talented – Editor]
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Ultimately, we decided to use the
KISS principle (“keep it simple, stupid”) and, if people enjoy the oldschool goodness of our take on a Stylophone, we could develop a new-
fangled version later. Our Styloclone
comprises a PCB, a stylus and an
optional case, as shown in the photos.
The original Sylophone circuit has
two main parts. The first is a simple
oscillator in which the stylus changes
the RC time constant to play the
notes. The secondary vibrato oscillator causes the note frequency to vary
slightly but rapidly, making the sound
more interesting. You may recognise
the concept of vibrato as it is applied
to many instruments, including the
human voice.
Early Stylophones used a unijunction transistor for the note oscillator
August 2024 27
Fig.1: the Styloclone circuit uses just two ICs and one transistor. IC1 is the main oscillator that produces a note when
the stylus wired to CON3 touches one of the keypads, shorting a point in the resistor string to ground. The vibrato
oscillator is based on transistor Q1; it varies the voltage at pin 5 of IC1, modulating the frequency at around 7Hz. VR1
is for calibration, VR2 for tuning and VR3 for volume control.
but those are rare these days. Later
versions used a 555 timer IC, which
remains super common today, so we
have also used one.
The original approach is a masterclass in squeezing as much as possible
from the minimum number of parts.
We kept the essence and added a few
new parts to make a modern, buildable
project. That includes a simple output
amplifier, allowing us to use a standard
8W speaker. The original circuit used
a high-impedance speaker, which is
now difficult to obtain.
We are using an LM386 amplifier, which is hardly dragging the
28
Silicon Chip
Stylophone into the 21st century, as
that part has been around since the
mid-1970s. The LM386 itself has some
fame in the musical domain as a very
common IC in guitar practice amplifiers and distortion boxes, so it is a
fitting choice.
You can hear some audio clips of the
prototype Styloclone at siliconchip.
au/Shop/6/432 but remember that I am
more of an engineer than a musician,
so don’t expect the Brandenburg Symphony! Still, they should give you an
idea of the tone it produces if built as
described here. It’s possible to make
some simple modifications to change
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the tone, some of which will be mentioned later.
Circuit details
The resulting circuit is shown in
Fig.1. There are two oscillators, one
for vibrato and the second to generate the notes. The vibrato oscillator is
built around BC549 transistor Q1, with
100nF capacitors and 68kW resistors
forming a feedback network. The result
is a very simple phase-shift oscillator.
Early Stylophones used a 10MW
pull-up resistor on the base of Q1 to
bias this amplifier, which is effective
but subject to significant variation. We
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Scopes 1 & 2: the left scope shows the 1µF capacitor being charged and discharged by the 555 timer (cyan) and the output
voltage being delivered to the speaker for a 440Hz A note (yellow). The control voltage (mauve) is about 5.3VDC in this
case, although there is about 50mV AC superimposed on it from the output. The right scope shows the same signals as in
Scope 1 but with a faster timebase and with vibrato enabled, visible as a periodic shifting of the waveform.
have used a slightly more complex
arrangement that ensures a defined
setpoint for the vibrato oscillator. It
should work for any high-gain NPN
transistor similar to the BC549.
The vibrato can be switched on and
off using S2, which shorts the collector
of Q1 to ground. This is a brutal but
effective way of stopping this oscillator. We will discuss how the vibrato
works as we describe the main oscillator.
The main oscillator in the original
Stylophone used a programmable unijunction transistor in the main oscillator, although early updates replaced
that with the NE555 timer IC, which
came out in about 1972.
The 555 is set up as an astable
multi-vibrator, which is a fancy way of
saying that it oscillates continuously.
For now, let’s look at it with the vibrato
switched off and the tuning potentiometer at its midpoint. Note that the 555
will work just fine without the tuning
potentiometer but without the ability
to adjust the tuning.
In this case, with the pen not touching any of the keyboard pads, both
the trigger and threshold inputs are
pulled to ground via trimpot VR1 and
the long string of series resistors that
ultimately connects to 0V. Referring to
Fig.2, the output of Comparator C goes
low, while Comparator T’s goes high.
The RS flip-flop is reset, so OUT goes
low. The output buffer inverts this, so
the 555 output goes high.
It remains in this state while no note
is selected. When the stylus touches
the keyboard, it connects the 555 output to part of the resistor string that
defines each note. The 1µF timing
capacitor charges via these resistors,
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with the charge rate determined by
the resistance in the string (ie, the
note selected).
It continues to charge until the voltage on the Threshold pin exceeds the
Control voltage and the Comparator C
output goes high. The RS flip-flop is
reset, and the OUT pin goes high, so
the 555 output pin goes low. The 1µF
capacitor starts to discharge via the
resistor string.
Once the voltage goes below the
Comparator T positive input reference
voltage, the Comparator T output goes
high again, setting the RS flip flop. This
drives the output high, and the whole
process repeats. The resulting oscillation is demonstrated in Scope 1.
There are a few tweaks to the operation of the 555 IC in a Stylophone. The
first is that the control voltage (CV) pin
is connected to the wiper of a potentiometer. This varies the control voltage, which changes the voltage over
which the 1µF capacitor must charge
over the oscillation cycle, allowing the
Styloclone to be tuned.
We have selected resistors for each
note that are in tune with middle A at
440Hz, as long as the 1µF capacitor is
reasonably accurate. The tuning works
well, but this is a very simple circuit,
so if you set the tuning pot very high
or low, you will find the octave is a
bit off. We have selected values for
the keyboard resistor string that give
very close to in-tune notes.
The second tweak is that the vibrato
oscillator is capacitively coupled to
the 555’s control voltage input. This
adds an AC component to the control
voltage and modulates the charge/
Fig.2: the 555 timer generates two reference voltages at 1/3 and 2/3 of its
supply voltage, which are fed to the inputs of two comparators. The outputs
of those comparators control a flip-flop, which in turn controls the output
voltage. The discharge transistor switches on when the output is low.
Australia's electronics magazine
August 2024 29
The desktop
version of our
Styloclone doesn’t need a
case, keeping it simple and pure! It
uses four standoffs in the corners for feet.
discharge range required for the 1µF
capacitor, as seen in Scope 2.
Tuning calculations
Getting the notes right took a lot
of work. The standard formula for
oscillation frequency for a 555 timer
is f = 1.44 ÷ (C × [Ra + 2 × Rb]). With
the tweaks to the circuit, such as not
using the discharge circuit, we found
we needed to use f = 0.5823 ÷ (R × C).
This is because we are not charging
from Vcc and discharging to ground
but instead using the 555 output as
the charge/discharge source.
Even then, there was non-linearity
across the scale; we were able to use
this formula to get close to the right
resistances, but then we had to handtune the values.
We were conscious that this might
introduce variation in behaviour for
chips from different suppliers, which
may have differing high and low output voltages. To test this theory, we
drove around town and bought five
different chips from various suppliers and batches. We verified that the
resistances we chose worked for all
of these with only minor variations.
The fact that Stylophones have
been made this way for years should
have told us that we were jumping at
shadows.
30
Silicon Chip
Our choice of a 1µF timing capacitor
in the oscillator defined the resistances
required for each note. Some rather
odd resistances are required. Table 1
shows each note’s ‘ideal’ frequencies
and incremental resistances. Because
the resistance is in a string, we have
worked out the best-fit values from the
E24 resistance range.
As expected, there are minor errors.
While these errors are not huge, they
indicate there is no benefit in being
overly anxious about achieving the
exact modelled resistances. So, you
can use 1% E24 resistors of the specified values; there is no need for more
precision than that.
We considered having one potentiometer per note, but even the cheapest trimpots would have cost more
than 10 times that of simple resistors.
It would have also made tuning very
complicated!
If you choose to fine-tune your Styloclone by varying the resistor values,
remember to set the tuning control
to your ‘zero point’ and keep it there
while you select new resistors. You
must start with the highest note and
then work down the scale. All the tuning resistors add up, so if you go back
and change a higher note, you need to
retune all the lower notes.
We have lined all these resistors
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up alongside each note on the board.
Make sure you check each value as you
go and don’t put any in the wrong spot,
or the tuning will end up all wonky.
The original Sytlophone used a
high-impedance speaker. We have
added an amplifier and optional line
output in case you want to record a hit
song with your Styloclone. The circuit
around the LM386 is bog standard,
and the only part warranting comment is the 1µF capacitor from its
pin 3 to ground that rolls off the
high-frequency response.
The resulting filter has
a pretty brutal corner frequency of around 190Hz.
The resistance of the RC circuit is
formed by the 1kW resistor in parallel
with the 4.7kW resistor from the volume control plus the volume control’s
resistance. This filter tones down the
harshness of the square wave output
a lot. If you want a brighter sound,
reducing this 1µF capacitor will give
you that.
We have used a simple 57mm
speaker for this device; they are cheap
and rugged. This speaker can produce
plenty of output, but if more sound
is required, you can certainly plug it
into your Marshall Stack via the mono
3.5mm jack.
The stylus
We have used yet another Biro (ballpoint pen) case as the stylus handle in
this project. This seems to be something of a tradition in the making!
As the tip, we used a 4mm Posidriv
machine screw (Altronics H3310; Phillips head would also be fine), to which
we soldered the stylus lead. We then
glued it into the tip of that obligatory
Biro case using Araldite epoxy – see
the photo below.
You might find another way of
doing this. For example, you could
simply place a small diameter heatshrink tubing around a stiff piece of
wire and bend the end back so it isn’t
sharp. However, if you use an alternative approach, ensure that the player
is insulated from the stylus tip, as
The stylus is made from a Biro
(ballpoint pen) case, an M4
machine screw and siliconeinsulated wire soldered to the end
of the screw.
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otherwise, skin resistance and body
capacitance could interfere with its
operation.
Our goal was to make a conductive stylus tip that did not have sharp
edges that would scratch and wear the
PCB ‘keys’.
For the stylus wire, we used
super-flexible silicone-insulated wire
on the assumption that the lead will
be waved around a lot. We don’t
want the lead breaking! The Altronics W2400-W2407 wire (the last digit
determines the colour) has 95 strands
with silicone insulation and is made
for this sort of application (well, meter
leads etc).
The large number of thin wires in
the wire will make this very tolerant
of flexing and maximises the fatigue
life. The length of the stylus lead can
be tweaked, but 600mm feels about
right to us.
To attach the wire to the screw, we
held the screw in a vise, applied flux
to end top of the screw and tinned it.
We then soldered the flexible wire to
the end of the screw.
We have included two 4mm holes
in the PCB to secure the stylus lead
using a zip/cable tie in front of the
stylus connector. This allows you to
run the stylus lead through a simple
hole you drill in the side of the case
without the risk of it being pulled too
hard and damaged. We recommend
you select a side to suit your right- or
left-handed preference.
perhaps mount it onto a piece of timber or other board.
You need to decide which version
you want to build before starting construction since the circuits are identical but the board layouts are quite
different.
Case preparation
For the case-mounting version, we
have put in some effort so that mounting the board is easy. The hardest part
is neatly cutting the rectangular hole
in the case to access the keys. We’ll
describe how to prepare the case before
assembling the PCB, as it might be
easier to do it first. You can skip this
section if you are building the version
without the case.
The best approach to cutting the
large hole is to mark its outline on
the case, then drill 6mm holes in each
corner 3mm inside the actual corner
junction, so the edges of the holes align
with the cutout. Next, use a hand saw
or rotary tool to cut just inside the
lines. You can then file the hole to size.
ABS plastic works very easily and
does not clog files too severely, so tidying up the hole is a lot easier than you
might expect. The drawing for the front
panel cutout and drilling is in Fig.3.
I used a really sharp knife and ruler
to score each line, but you have to be
very careful not to slip and cut your
fingers while doing that! If you cut like
this repeatedly, you can actually go all
the way through the plastic.
If you decide to do that, we suggest
you wear chainmail (mesh) gloves.
We are not making this up; chefs use
them to avoid cutting their fingers.
They are readily available, not too
expensive, and surprisingly flexible.
Search for “cut-resistant gloves” or
“chef’s gloves” to find them.
The remainder of the case preparation is drilling the speaker holes on
the top panel, plus the switch and
potentiometer holes in the rear panel.
We found it kind of fiddly to get
the measurements right for the rear
panel, which is at an angle to the front
panel and has rounded edges. So be
Table 1 – Styloclone note ideal frequencies, resistors & actual frequencies
Note
Ideal
Resistor Running total Measured
Error
Error (%)
B
493.9Hz
68Ω
1179Ω
493Hz
-0.9Hz -0.3 to -0.1
A♯
466.2Hz
68Ω
1247Ω
466Hz
-0.2Hz -0.2 to +0.1
A
440.0Hz
75Ω
1322Ω
440Hz
0.0Hz
-0.1 to +0.1
G♯
415.3Hz
82Ω
1404Ω
416Hz
0.7Hz
+0.0 to +0.3
G
392.0Hz
82Ω
1486Ω
394Hz
2.0Hz
+0.4 to +0.6
F♯
370.0Hz
91Ω
1577Ω
371Hz
1.0Hz
+0.1 to +0.4
Case options
F
349.2Hz
91Ω
1668Ω
351Hz
1.8Hz
+0.4 to +0.7
We have produced two slightly different PCB designs. The first, coded
23106241, fits into an Altronics H0400
case sloped instrument case and
allows you to mount the board to the
front panel using the inbuilt mounting
holes. It gives a neat finish and delivers a neatly packaged product.
The way this board mounts requires
all the components to be placed on the
back of the board, with the ‘keys’ on
the front of the board so they can be
presented to the user through a large
rectangular hole in the case.
However, we recognise that the case
costs more than all the electronic components, and it isn’t strictly required.
So the other PCB option, coded
23106242, has all the components on
the top side of a rectangular board,
with holes in the corners to use 10mm
Nylon standoffs as feet. This way, you
can set it on a flat surface to play it or
E
329.6Hz
100Ω
1768Ω
332Hz
2.4Hz
+0.6 to +0.9
D♯
311.1Hz
120Ω
1888Ω
312Hz
0.9Hz
+0.1 to +0.5
D
293.7Hz
120Ω
2008Ω
294Hz
0.3Hz
-0.1 to +0.3
C♯
277.2Hz
120Ω
2128Ω
278Hz
0.8Hz
+0.1 to +0.5
C
261.6Hz
120Ω
2248Ω
264Hz
2.4Hz
+0.7 to +1.1
B
246.9Hz
130Ω
2378Ω
251Hz
4.1Hz
+1.5 to +1.9
A♯
233.1Hz
150Ω
2528Ω
236Hz
2.9Hz
+1.0 to +1.5
A
220.0Hz
150Ω
2678Ω
223Hz
3.0Hz
+1.1 to +1.6
G♯
207.7Hz
180Ω
2858Ω
210Hz
2.3Hz
+0.9 to +1.3
G
196.0Hz
180Ω
3038Ω
198Hz
2.0Hz
+0.8 to +1.3
F♯
185.0Hz
200Ω
3238Ω
186Hz
1.0Hz
+0.3 to +0.8
F
174.6Hz
200Ω
3438Ω
175Hz
0.4Hz
-0.1 to +0.5
E
164.8Hz
200Ω
3638Ω
164Hz
-0.8Hz -0.8 to -0.2
D♯
155.6Hz
200Ω
3838Ω
155Hz
-0.6Hz -0.7 to -0.1
D
146.8Hz
220Ω
4058Ω
147Hz
0.2Hz
-0.2 to +0.5
C♯
138.6Hz
220Ω
4278Ω
139Hz
0.4Hz
-0.1 to +0.6
C
130.8Hz
240Ω
4518Ω
131Hz
The Error column has an uncertainty of ±0.5Hz.
0.2Hz
-0.2 to +0.5
siliconchip.com.au
August 2024 31
cautious with this; perhaps start with
smaller holes than required and be
prepared to file them to a final size.
Fig.4 shows the drilling details for
the rear panel.
Regarding labelling, we were on a
roll with the retro feel of this project
and had just purchased a 3D printer
for the young enthusiast. So we got out
the 3D modelling software and made a
cool label for the project. We reckon it
looks pretty good. The STL file is available from siliconchip.au/Shop/11/434
Note that it needs to be printed at
a 5% scale, a simple selection in the
Cura slicer program.
You could probably use super glue
to attach the PLA 3D-printed parts
to the ABS plastic case, but we read
that you can melt ABS plastic in acetone to make “ABS glue”. We picked
up some of the swarf from drilling
the front panel, put it in a teaspoon
of acetone and mixed until we had a
thick, sticky liquid.
We dabbed it onto the back of the
PLA labelling and carefully placed it
on the front panel, where it stuck perfectly. Get it in the right spot when
you put it down and do not move it.
PCB assembly
Building the Styloclone electronics
is pretty straightforward. All parts are
through-hole types, and we have used
larger pads where possible to facilitate
soldering.
First, check that you have the correct
PCB, either the one coded 23106241
that measures 179 × 123mm for the
case-mounting version or the standalone board that’s coded 23106242
and measures 207 × 124.5mm. Figs.5
& 6 are the PCB overlay diagrams for
the two versions that show where all
the components go.
The best place to start is with the
resistors. We have had to use several
E24 resistors with less-familiar values
like 91W, 200W etc. These are used to
get the tuning right for each note, so
you really need the specified parts.
Altronics and Jaycar stock these E24
values, and the larger online suppliers like Mouser, DigiKey, RS and element14 have them too.
When fitting these, we recommend
measuring each part’s resistance as
you go since the colour codes can be
tricky to read sometimes. If you get a
part in the wrong spot, you will find
that some of the notes are out of tune.
Once all the resistors are in place, add
1N5819 schottky diode D1 (taking care
to match its orientation to the overlay)
and the 200W trimpot.
At this point, it is convenient to
mount the 555 and LM386 ICs. Do this
before the capacitors, as it will give
Fig.3: cutting the large rectangular hole is the fiddliest part of the project. We used a Dremel cutting tool and file for ours.
The easiest way is to mark and drill the corner holes for the cutout from the inside, then do the remainder of cutting and
drilling from the outside. If you need an inside template, you can print this out mirrored. Regardless, double-check which
side you drill the speaker holes on. All dimensions in this diagram are in millimetres.
32
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
Shown at left is a view of the case-mounting version inside the case, from
the underside, where the components live. The keyboard is accessible through
a cutout on the other side. The finished Styloclone is shown above in its case.
This version in a box gives much richer sound than the free standing version.
you more room to get them in place.
The 555 and LM386 look the same, so
you will need to check the part numbers and ensure they are both the right
way around. The dot or indent on the
chips goes to the top of the board, and
the PCB silkscreen has dots in nearby
positions to help you.
It is then time to install the capacitors. Make sure you use film capacitors for values up to 1µF; either MKT
or greencaps will work fine, although
greencaps may need their leads bent to
fit the pads. Do not use ceramic capacitors, as they have a huge temperature
coefficient and large values can even
be microphonic.
The 1µF capacitor on pin 2 of the
555 is particularly critical; it must
be close to 1µF, so use a part with a
decent tolerance (5% if possible; failing that, 10%).
After that, you can add the electrolytic capacitors. Make sure each one
is the right way around, with the longer positive lead on the side with the
+ symbol. The stripe on the can indicates the negative side, so it should be
opposite the + symbol in each case. To
make this process easier, all capacitors
are orientated in the same direction.
Next come the two 5mm screw terminals and the battery clip. We like
to make connections to offboard components using terminals as it makes it
easy to service, but you could simply
solder flying leads to the board if that
suits you. Put a dab of neutral-cure
silicone sealant under the battery clip
before you solder it to the board, as
that will keep it secure when the Styloclone is in use.
We have added two 4mm holes on
either side of the battery, allowing you
to ‘zip tie’ it to the board so it can’t
come out during transport.
Now fit the two switches. We have
used PCB-mounting switches from
Altronics. Similar switches are available from Mouser and other larger
suppliers; you could run flying leads
from the PCB pads to panel-mounted
switches in a pinch.
Two similar but not identical
types of potentiometers are used: a
5kW linear type for the tuning control and a 5kW logarithmic type for
the volume control. Both are standard 16mm-size devices. The volume
pot will be labelled A5K, where A
Fig.4: the drilling details for the Styloclone’s rear panel. This is the top of the case; the front panel is at the bottom in this
drawing. All measurements are referenced to the top of the fixing post on the left.
siliconchip.com.au
Australia's electronics magazine
August 2024 33
MINI SPEAKER
E
A#
G#
F
G
D2#
C2#
B
A
C2
G2#
F2#
D2
E2
3.3kW
D
C
F#
D#
C#
TUNE
F2
G2
A2#
A2
B2
VOLUME
VR3 5kW log.
+
1kW
10kW
100nF
REAR OF
MINI SPEAKER
100nF
68kW
100nF
68kW
100nF
4.7kW
Q1
BC549
+
100mF
FINE
CON2
TUNE
SPEAKER
240W
220W
220W
200W
200W
200W
200W
180W
270kW
180W
130W
STYLUS
TP2
100W
91 W
91W
82W
82 W
75 W
68W
68W
100nF
1kW
100nF TP1
VR1
200W
CON3
120W
+
2.7W
TO STYLUS
470mF
120W
+
220mF
1m F
120W
100nF
IC1
555
120W
IC2
LM386N
1kW
5819
D1
150W
BAT1
9V BATTERY
HOLDER
VR2
5kW
lin.
4.7kW
1kW
120kW
47kW
10 m F
4.7kW
100nF
1mF
S2
150W
S1
CON1
VIBRATO
POWER
OUTPUT
FRONT OF BOARD
C
B2
UNDERSIDE OF BOARD (TRUNCATED)
34
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
Fig.5: here is where to fit all the components for the case-mounting version of
the Styloclone. In this version, all parts mount on the bottom while the ‘keys’
are on the top. Take care with the orientations of the diode, ICs and electrolytic
capacitors and make sure you don’t mix up all the different-value resistors!
240W
C
C#
D#
E
MINI SPEAKER
200W
200W
F#
200W
270kW
200W
F
3.3kW
180W
4.7kW
150W
+
A#
B
150W
GND
1kW
100nF
130W
FINE
TUNE
120W
120W
VR1
200W
VOLUME
100nF
CON3
STYLUS
1mF
IC1
555
100nF
E2
120W
100W
TP1
OUTPUT
1m F
IC2
LM386N
220mF
VR3
5kW
log.
+
470mF
1kW
D2#
10mF
100nF
120W
D2
S2
VIBRATO
68kW
C2
C2#
100nF
68kW
VR2
5kW
lin.
1kW
A
Q1 100nF
BC549
4.7kW
47kW
100mF
120kW
SPEAKER
4.7kW
180W
1kW
G#
TUNING
10kW
G
+
100nF
CON1
91W
F2
82W
G2
G2#
82W
100nF
BAT1
TP2
9V BATTERY HOLDER
+
75W
A2
D1
A2#
5819
68 W
POWER
68W
S1
►
B2
91W
–
F2#
2.7W
►
siliconchip.com.au
220W
D
Testing your Styloclone
Once all the parts are in, insert a
fresh battery and measure the voltage
across it. It should be near 9V. If the
voltage is low, look for parts getting
hot; if none are, pull the battery out
and check that it is fresh.
With the voltage rail all good, set the
volume and tuning controls to midrange and touch the stylus to one of
the key pads. You should hear a tone.
Run up and down the keys and you
should get a reasonable set of notes.
If you get nothing:
220W
+
indicates “Audio Taper”, while the
tuning pot is linear and will be labelled
“B5K”. Do not get these mixed up.
If you intend to plug the Styloclone
into an amplifier or recorder, mount
the 3.5mm socket now. If you will
never use it, you can save yourself a
bit of money and leave it off.
We used a thin bead of neutral-cure
silicone sealant around the hole in
the PCB to attach the speaker. After
applying the sealant, gently push the
speaker into place. An alternative is
to use 5-minute Araldite (or another
epoxy glue), which works a treat and
is pretty permanent. The speaker must
go in so that the cone is visible from
the same side as the tin-plated ‘keys’.
If building the board designed to
mount in the case, the speaker will
be inserted from the opposite side of
the board to the majority of the components, so the magnet comes through
to the same side as the components
and the cone can present through the
front panel.
If you are building the standalone
board, the speaker is inserted from
the same side as the components, and
the magnet will be on the underside
of the board.
Once you glue the speaker in, take
a break and ensure your glue cures.
Once that silicone cures, the speaker
will never fall out, but until then, it
will fall out and make a mess of everything near it. Don’t ask me how I know!
Solder wires to the speaker terminal and screw them into the speaker
header; it doesn’t matter which way
around they go. Also connect a wire
to the stylus connector for testing.
Depending on whether you are left- or
right-handed, drill a 3mm hole for your
stylus wire to go through in one side
of the case. This should be on the top
half of the case, about halfway down
the length.
Fig.6: for the standalone (non-case) version of the Stylophone, all parts mount
on the top side, which also has the keyboard. All the same parts are used in
both versions. Again, watch the orientations of the diode, ICs and electrolytic
capacitors and make sure you don’t mix up all the different-value resistors.
Australia's electronics magazine
August 2024 35
T Check the voltage on pin 8 of IC1,
the 555 timer. It should be more than
8V. If not, then something is wrong
with the power supply. Is it on? Is
diode D1 the right way around?
T Is IC1 indeed a 555 and is it the
right way around?
T Check that pin 5 of IC1 is between
4V and 6V. The tuning pot sets this, so
try adjusting that. It does not need to
be exact, but it should not be pegged
to one of the rails.
T Check for an AC voltage on pin
3 of IC1. This will be a square wave.
T If there is a voltage there, trace
through the 10µF capacitor to the
clockwise terminal of volume control
VR3, then to its wiper and on to pin
3 of IC2, the LM386. Try turning the
volume up if you lose the signal at the
wiper of VR3.
T Check pin 6 of IC2 for 8-9V DC.
If this is not present, track back to the
battery again.
T Check pin 5 of IC2 for an AC voltage. If this is present, is the output
capacitor the right way around, and
is the speaker wired up properly? Are
its terminals shorted?
If the notes are all wrong:
T Check that 200W trimpot VR1 on
the board is set to around 110W. You
should measure close to 1110W across
test points TP1 and TP2, which are just
below the battery (this measures VR1
and a 1kW series resistor).
T Check that the correct values have
been used for the row of resistors near
the keys.
T Set the tuning potentiometer,
VR2, to about 2/3 scale. Turn the Styloclone on and measure the voltage at
pin 5 of the 555 timer. This should be
about 5.3V. If not, adjust the trimpot
and see if it can be set to about 5.3V.
Check that you have not swapped the
linear and log pots.
T Touch the stylus to the high B.
You should get a reasonably high
note at around 494Hz. If this is way
off, check the value of the 1µF timing
capacitor. If this note is wrong, every
other note will also be wrong.
T Assuming the high B is OK, run
along the notes going down the scale.
If you find a wrong note, check the
associated resistor and correct the
problem. Repeat until they are all
correct.
T Remember that all lower notes are
built on the preceding notes, so you
should only fix a resistor associated
36
Silicon Chip
Parts List – Styloclone
1 134 × 189 × 55mm sloping ABS desktop instrument case
[Altronics H0400] OR
4 M3 × 10mm tapped Nylon spacers
1 double-sided PCB coded 23106241 (case version), 179 × 123mm OR
1 double-sided PCB coded 23106242 (standalone version), 207 × 124.5mm
1 57mm diameter 8Ω 700mW loudspeaker (SPK1) [Altronics C0610]
2 PCB-mount right-angle miniature SPDT toggle switches (S1, S2)
[Altronics S1320]
1 200Ω top-adjust mini trimpot (VR1)
1 5kΩ 16mm single-gang linear (B5K) potentiometer (VR2)
1 5kΩ 16mm single-gang logarithmic (A5K) potentiometer (VR3)
1 PCB-mount 9V battery holder (BAT1) [Altronics S5048]
1 PCB-mount 3.5mm SPST chassis-mount mono jack socket
(CON1; optional) [Altronics P0090]
2 2-way 5mm/5.08 miniature PCB-mounting terminal blocks (CON2, CON3)
4 M3 × 6mm panhead machine screws
4 M3 shakeproof (star) washers
1 ballpoint pen case
1 short M4 panhead machine screw
1 9V battery
2 short 2.5mm- or 3.5mm-wide cable ties (‘zip ties’)
1 60cm length of white silicone-insulated hookup wire
(outside diameter ~2.5mm) [Altronics W2407]
Semiconductors
1 555 timer IC, DIP-8 (IC1)
1 LM386N mono amplifier IC, DIP-8 (IC2)
1 BC549 30V 100mA NPN transistor, TO-92 (Q1)
1 1N5819 40V 1A schottky diode (D1)
Capacitors (16V electrolytic unless noted)
1 470μF
1 10μF 50V electrolytic
1 220μF
2 1μF ±5% 63V/100V MKT
1 100μF
8 100nF 63V/100V MKT
Resistors (all 1/4W 1% axial unless noted)
1 270kΩ
4 1kΩ
4 120Ω
1 120kΩ
1 240Ω
1 100Ω
2 68kΩ
2 220Ω
2 91Ω
1 47kΩ
4 200Ω
2 82Ω
1 10kΩ
2 180Ω
1 75Ω
3 4.7kΩ
2 150Ω
2 68Ω
1 3.3kΩ
1 130Ω
1 2.7Ω (5% OK)
with a wrong note if all the notes above
it are correct.
Switch on the vibrato using switch
S2 and check that you get a warbling
effect. Now you should have a working Styloclone.
We used VR1 and VR2 to tune the
upper A on our unit to 440Hz. At this
frequency, the resistors we selected
have pretty much the whole range
of notes in tune (just as importantly,
you’ll be in tune with a concert grand
piano). The tuning process is:
1. Using a DMM, adjust trimpot
VR1 to achieve 1110W between TP1
and TP2.
2. Adjust tuning potentiometer VR2
to get 440Hz at pin 3 of IC1 when the
Australia's electronics magazine
upper A is played. If you have a frequency meter, probe the speaker output.
3. Check that the other notes are in
tune. If they are not, use a DMM to
check the associated resistor values.
How long will the battery last? That
depends on how loud you play it.
When switched on but not playing a
note, ours drew 8.5mA. A typical 9V
battery would idle for about 50 hours
before going flat. At moderate volumes, the current draw increases to
about 60mA, which means it should
provide about 3-6 hours of playing
time.
You should now be set to go and
create your masterpiece!
SC
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