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The Styloclone
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
Practical Electronics | June | 2025
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’.
Ultimately, we decided to use
the KISS principle (“keep it simple,
stupid”) and, if people enjoy the
old-school goodness of our take on
a Stylophone, we could develop a
new-f angled version later. Our Styloclone comprises a PCB, a stylus
and an optional case, as shown in
the photos.
The original Stylophone 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
but those are rare these days. Later
versions used a 555 timer IC, which
3
Constructional Project
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.
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 Stylophone into the 21st century, as that
part has been around since the mid4
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
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 phaseshift oscillator.
Early Stylophones used a 10MW pullup resistor on the base of Q1 to bias this
amplifier, which is effective but subject
to significant variation. We have used
a slightly more complex arrangement
that ensures a defined setpoint for the
Practical Electronics | June | 2025
The Styloclone
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.
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 multivibrator, 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, with the
charge rate determined by the resistance in the string (ie, the note selected).
Practical Electronics | June | 2025
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 volt-
age, 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/discharge
range required for the 1µF capacitor,
as seen in Scope 2.
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.
5
Constructional Project
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.
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.
Our choice of a 1µF timing capacitor
in the oscillator defined the resistances required for each note. Some rather
6
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
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 highimpedance 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 (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
otherwise, skin resistance and body
The stylus is made from a Biro
(ballpoint pen) case, an M4
machine screw and siliconeinsulated wire soldered to the end
of the screw.
Practical Electronics | June | 2025
The Styloclone
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 superflexible silicone-insulated wire on
the assumption that the lead will be
waved around a lot. We don’t want
the lead breaking! The wire I used
has 95 strands of copper with silicone insulation and is made for this
sort of application (well, multimeter
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.
Case options
We have produced two slightly different PCB designs. The first, coded
23106241, fits into a Gainta G1183
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 as a bare electronic
assembly, or perhaps mount it onto
Practical Electronics | June | 2025
a piece of timber or other type of
stiff 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
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
F
349.2Hz
91Ω
1668Ω
351Hz
1.8Hz
+0.4 to +0.7
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
130.8Hz
240Ω
4518Ω
131Hz
The Error column has an uncertainty of ±0.5Hz.
0.2Hz
-0.2 to +0.5
C
Error (%)
7
Constructional Project
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 ac-
etone 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.
Most local retailers stock these E24
values, and the larger online suppliers like Farnell, Mouser, DigiKey and
RS 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.
8
Practical Electronics | June | 2025
The Styloclone
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 a
local supplier. 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 indicates “Audio
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.
Practical Electronics | June | 2025
9
Constructional Project
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
91W
91 W
82 W
82W
75W
68 W
68 W
B2
100nF
1kW
100nF TP1
VR1
200W
CON3
120W
+
2 .7 W
TO STYLUS
470mF
120W
+
2 20 m F
1m F
120W
100nF
IC1
555
120W
IC2
LM386N
1k W
5819
D1
150W
BAT1
9V BATTERY
HOLDER
VR2
5kW
lin.
4.7kW
1kW
120kW
47kW
10mF
4.7kW
100nF
1mF
S2
150W
S1
CON1
VIBRATO
POWER
OUTPUT
FRONT OF BOARD
C
UNDERSIDE OF BOARD (TRUNCATED)
10
Practical Electronics | June | 2025
The Styloclone
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
+
B
GND
100nF
130W
FINE
TUNE
120W
120W
VR1
200W
CON3
STYLUS
1mF
IC1
555
120W
100W
10mF
TP1
OUTPUT
1m F
IC2
LM386N
220mF
VR3
5kW
log.
+
470mF
1kW
E2
VOLUME
100nF
100nF
D2#
S2
VIBRATO
100nF
120W
D2
1kW
68kW
C2
C2#
100nF
68kW
VR2
5kW
lin.
1kW
A#
150W
4.7kW
A
Q1 100nF
BC549
120kW
47kW
100mF
4.7kW
TUNING
SPEAKER
1kW
G#
180W
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
►
Practical Electronics | June | 2025
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
+
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.
11
Constructional Project
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?
Is IC1 indeed a 555 and is it the
right way around?
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.
Check for an AC voltage on pin
3 of IC1. This will be a square wave.
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.
Check pin 6 of IC2 for 8-9V DC.
If this is not present, track back to the
battery again.
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:
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).
Check that the correct values have
been used for the row of resistors near
the keys.
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.
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.
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.
Remember that all lower notes
are built on the preceding notes, so
you should only fix a resistor associ12
Parts List – Styloclone
1 134 × 189 × 55mm sloping ABS desktop instrument case
[Gainta G1183B(UL), available from TME] 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 (2¼-inch) diameter 8Ω 700mW+ loudspeaker (SPK1)
2 PCB-mount right-angle miniature SPDT toggle switches (S1, S2)
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)
1 PCB-mount 3.5mm SPST 3-pin mono jack socket (CON1; optional)
[SCHURTER 4832.222, Farnell 152206]
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)
Semiconductors
1 555 timer IC, DIP-8 (IC1)
1 LM368N 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)
ated 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 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
PE
create your masterpiece!
Practical Electronics | June | 2025
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