By
John
Clarke
ELECTRONIC
Wind Chimes
Aaaah . . . wind chimes! They’re so soothing . . . listening to the random
notes as the wind creates its own melodies. But what do you do if there’s no
wind? Aim a fan at it? We have a better idea: our Electronic Wind Chimes
removes your reliance on the wind, and even gives you the possibility of
playing tunes using the wind chime, enriching the experience!
T
his circuit drives a wind
When using a good-quality wind
chime, the clapper will enhance the
sound. A low-quality wind chime will
have the sound spoiled by the clapper,
where it produces an entirely different tone to the resonance sound of the
chime tube.
Often, the clapper is a circular piece
of timber with a bevelled edge, so that
a small area of its side strikes the tube.
Timber clappers are much better than
metal types. Once struck by the clapper,
a chime tube will move away from its
resting position due to kinetic energy
transfer. The chime tube will resonate
Wind chime basics
to produce sustained tones that differ
Wind chimes play a series of notes
from the initial strike sound.
that are generated by a clapper striking
If you are after more detail on wind
the sides of chime tubes. These tubes
chimes, the science behind them and
hang freely, so they
how to build them,
can resonate at their Features and specifications
a good site to visit
tuned frequency when • Drives wind chimes with up to 12 elements (or multiple smaller chimes) is: www.leehite.org/
struck. The clapper is • Suits a wide range of sizes from miniature chimes up to large ones
Chimes.htm
moved by a sail, which • Individual calibration of solenoid drive control parameters
This includes calis driven by the wind. • Sequence recording and playback
culators to design a
Fig.1 shows the basic • Sequences with long delays can be recorded in shorter periods
wind chime to produce
• Optional randomisation of the time between chime strikes
arrangement.
the desired notes. Be
• Adjustable randomisation parameters
The notes and sounds • Optional automatic switch-off in darkness
aware that the notes
are very dependent on
perceived from a wind
chime using solenoids. It does
so in a way that neither affects
the tonality of the result, nor prevents
the chimes from being operated by the
wind in the normal way. So you get the
best of both worlds.
More good news is that electronically,
it is fairly simple and uses readilyavailable parts. So you should not have
difficulty building it, nor is it likely to
break the bank. However, you will need
a degree of mechanical skill to make it.
Read on to understand why this is so.
30
chime tube length, thickness and diameter and the hanging point.
The frequency is higher with smaller
wind chimes – these tinkle away with
a light breeze, producing high-pitched
notes at a fast rate. Larger wind chimes
produce lower-frequency tones at a
slower rate.
Wind chime sound quality is also dependent upon the clapper. Its mass, density, shape and what it is made from very
much determines what sound you get.
Tonal differences can be demonstrated by tapping the chime tube with
various implements such as a screwdriver blade, screwdriver handle and
various pieces of timber. Compare the
resulting sounds against that produced
by the original clapper.
Practical Electronics | February | 2022
the wind chime is not significantly
prevented from its normal operation of
playing sounds due to wind.
So building this device involves some
electronic assembly, mechanical fabrication and a little woodworking. The
electronic side involves the assembly
of a circuit board, initial solenoid calibration and other adjustments. On the
mechanical side, you need to arrange
the solenoids and other bits and pieces
to activate the clapper.
The woodworking aspect involves
making a frame to support these solenoid movements, which are arranged
around the outside of the wind chime.
Design features
Our Electronic Wind Chime circuitry
can drive up to 12 solenoids, so it can be
used to play up to 12 different chimes.
These chimes don’t have to be within
the same wind chime. You could use the
same circuitry to control two or more
wind chimes, so long as there are no
more than 12 chimes in total.
You can also mix and match solenoids
– for example, using smaller solenoids
for small chimes and larger solenoids for
larger chimes. Each solenoid can be independently set up for how it is driven.
There are two adjustments. One
controls the voltage applied to each
solenoid. This can be varied from the
full 12V down to near 0V via pulse
width modulation.
This feature is used to prevent the
solenoid from being too aggressive. A
lower voltage will slow down the solenoid action, so that the wind chime is
not sent into disarray.
The second adjustment is the duration the solenoid is driven. This needs
to be sufficient to allow it to produce a
strike against the chime and then pull
away before the chime tube returns.
The electronics includes the option
to manually ‘play’ the wind chime by
pressing small pushbutton switches.
These are useful during calibration,
to check whether each chime is being
struck correctly. But these switches
have another purpose – you can record
a sequence by manually playing the solenoids using these buttons, then play it
back later, to play a tune (for example).
The sequence of solenoids and the
period between each activation is recorded. There is also a facility to record
long breaks between solenoid strikes
without having to wait the full period.
This feature increases the period that’s
recorded by a factor of 10, so you can
record a very long, slow sequence in a
reasonable amount of time.
During recording, a variety of different sequences can be included. This will
decrease the perceived repetition as the
played-back sequence repeats in a loop.
chime can be very different from the fundamental resonance of each chime tube.
Solenoid drive
The biggest challenge in making a
solenoid-driven wind chime is in
maintaining the original sound quality.
While a wind chime could be played
using solenoids that directly strike the
chime tubes, the sound produced in this
manner is rather poor.
A very simple solenoid-driven wind
chime arrangement is shown in Fig.2.
The solenoid push ends can be arranged
to strike the chimes in a straight-line
wind chime, which can be made from a
disassembled wind chime. While this is
easy to build, apart from the poor sound
quality, it also has the disadvantage that
it can no longer be played by the wind.
A more complex solenoid-driven
wind chime, which retains the original
configuration, is shown in Fig.3. Good
sound quality is maintained by using
the solenoids to pull the clapper that, in
turn, strikes the tubes in a similar way to
when driven by the wind. Additionally,
Practical Electronics | February | 2022
Fig.1: in a standard wind chime, the
wind blows the sail which moves the
clapper, bringing it into contact with
the chime tubes. Each time it strikes
a tube, it makes a sound and then
bounces off, possibly hitting other
tubes. The result is a non-repetitive
series of tones, varying with the
strength and direction of the wind.
Fig.2: the easiest way to drive a
wind chime with solenoids would
be to rearrange the tubes in a row
and then place a row of solenoids
alongside. This is not a very good
approach, though, as the solenoid
plungers will make a different sound
when striking the tubes compared to
the (usually timber) clapper. Also,
this modified chime would no longer
work the same (or possibly at all)
when driven by the wind.
31
The recording time available is well
over what you might require. This
means that you are free to record without
concern of running out of memory. The
recording is permanently stored, unless
overwritten with a new recording.
There is also an option to randomise
the pauses between solenoid strikes
during playback. At the maximum
randomness setting, the delays vary
between one and five times longer than
those recorded.
The randomness changes to a new
value at intervals of between 10 seconds and 21.25 minutes; this, in itself,
varies randomly.
This is all designed to remove any hint
of a machine-driven wind chime, making
it sound more natural.
The maximum randomness values can
be changed to smaller values if desired.
Optionally, the Electronic Wind Chime
can be set to switch off during darkness.
This is useful if you (or your neighbors!)
prefer peaceful serenity at night.
Circuit details
The circuitry, shown in Fig.4, is based
around microcontroller IC1. It stores the
recorded sequences in its Flash memory,
then plays them back by using its digital
outputs to drive transistors or MOSFETs
that, in turn, drive the solenoids. The
microcontroller also monitors a lightdependent resistor (LDR1), a control
switch, jumper link and a trimpot and
drives a status LED (LED1).
12 of IC1’s 20 pins are used as digital
outputs for driving the solenoids. There
are two types of solenoid drivers you can
use. One option is NPN transistors for
driving low-current solenoids.
This is a considerable cost saving
compared to N-channel MOSFETs, but
MOSFET drivers must be used for solenoids that draw over 500mA.
There is a small circuit change when
using a transistor rather than a MOSFET:
the resistor value (R1-R12). When a
transistor is used, the resistor value is
2.2kW, which sets the transistor base
current. For a MOSFET, the resistor
value is 100W instead, and this drives
the MOSFET gate.
Diodes D1-D12 at the transistor
collector or MOSFET drain are there
to conduct the reverse voltage (backEMF) from the solenoid coil when it is
switched off. This protects the bipolar
transistor or MOSFET from damage.
PWM drive
The solenoids can be driven with a
PWM signal. This is where the MOSFET
or transistor is switched on and off at
500Hz with a particular duty cycle. The
average voltage produced is the duty
cycle multiplied by the supply voltage.
So for a 12V supply and a 50% duty
32
Fig.3: while more work to
achieve, this arrangement
is far superior as it
allows the chime to be
driven by the wind or
electronically, depending
on the weather and your
mood. It also retains
the original tone. The
solenoids now press
on levers that pull the
clapper via a string to
strike the associated tube.
A second set of strings
prevents the chimes
from swinging back
and striking the clapper
again, due to inertia,
unless the associated
solenoid is re-energised.
cycle, the average voltage applied to the
solenoid is 6V.
The frequency needs to be high
enough to prevent the solenoid from
driving the plunger in and out at the
PWM rate. But too high a frequency can
also cause problems such as increased
dissipation in the transistor/MOSFET
or reduced response from the magnetic
properties of the steel core.
Practical Electronics | February | 2022
l
l
Fig.4: the
circuit for the
Electronic Wind
Chime comprises
mainly microcontroller IC1
and transistors
Q1-Q24, which
are used to drive
the solenoids.
For each pair of
transistors (Q1
and Q2, Q3 and
Q4 etc), only
one is fitted. The
BC337s work up
to 500mA while
the MOSFETs
can handle up
to 3A. The rest
of the circuit
allows you
to set up the
unit, record a
sequence and
optionally,
have it switch
off at night.
l
SC
Electronic
L C Windchime
ONIC IN CHI
Ó
Our choice of 500Hz was suitable for a
wide variety of solenoids that we tested.
Oscilloscope waveform Scope1
shows the gate drive to the MOSFET
at the top (yellow) with a 5V drive
voltage. The drain voltage waveform
(blue) is the lower trace with a 12V
supply voltage. The solenoid has 12V
across it when the drain voltage is 0V,
and 0V across it when the drain is at
12V (the negative end of the solenoid
connects to the drain). The duty cycle
is around 50% at almost 500Hz.
The solenoid driver pins on IC1 usually are set as inputs. The MOSFET or
transistor is held off via the associated
10kW pull-down resistor. Having the
pins as inputs allows switches S1-S12
Practical Electronics | February | 2022
to pull the input high when pressed. If
the pin were set as a low output instead,
the pull-up switch would ‘fight’ the
microcontroller output, causing a high
current through the output pin.
The pin is changed to a high-level
output when required to switch on the
MOSFET or bipolar transistor. In this
case, pressing the associated switch will
not cause problems since the output is
already high.
For a low level, the pin is made an
input again, so the MOSFET or bipolar
transistor switches off (unless the associated switch is currently being pressed).
Note that pressing switches S1-S12
causes the associated solenoid to be
driven with the full 12V for the duration
that the switch is pressed. But when the
solenoid is driven via the microcontroller, the drive is a PWM waveform
with a preset on-period and duty cycle.
More circuit details
IC1’s pin 18 (digital input RA1) monitors
the LDR so that the circuit can optionally
switch off at night. During the daytime,
the LDR resistance is low, so pin 18’s
voltage is below the low threshold of
the RA1 input. A 100kW resistor and
trimpot VR2 form a voltage divider with
the LDR across the 5V supply.
This trimpot allows the detected light
threshold to be varied. When the LDR is
in darkness, the LDR resistance is high,
and this pull-up resistance causes the
33
Scope1: the 500Hz,
5V PWM drive to
the base/gate of the
output transistor
is shown in the top
trace (yellow) with
a 50% duty cycle,
and the resulting
(inverted) 12V
drive voltage to the
solenoid is shown
below in cyan.
The duty cycle (ie,
percentage of time
that the solenoid
receives current)
is adjustable for
each solenoid, to
control how hard it
is driven.
RA1 voltage to be above its high threshold. IC1 detects this, and the software
stops running.
The RA3 digital input monitors
control switch S13. This pin can be
used as an external master clear signal
(MCLR) or a general-purpose input. We
are using it as an input, and it is usually
pulled high, to 5V, by the 10kW resistor.
This input goes low when the switch
is pressed; it serves many functions, as
described later.
The status LED (LED1) is driven via
the RC1 output via a 1kW resistor. It is
used to indicate various modes when
recording a sequence and calibrating
the solenoid settings.
Trimpot VR1 is connected across the
5V supply, and its 0-5V wiper voltage is
monitored at IC1’s analogue input AN4
(pin 16). VR1 sets the solenoid pulse
width/duty cycle and drive duration
in conjunction with jumper JP1. JP1 is
monitored by IC1’s RA0 digital input
(pin 19).
This input is held high by the 10kW
pull-up resistor unless there is a shorting
link across JP1, which would pull it low.
two parallel 1000µF low-ESR capacitors, which helps to supply the peak
solenoid current.
Reverse polarity protection uses a
3A diode, D14. If the supply is connected backwards, this conducts to
blow the fuse.
The voltage to the remainder of the
circuit is applied via reverse polarity
protection diode D13, and is switched
by S14 before being applied to the input
of the 5V regulator, REG1. Two 100µF
capacitors, one at the regulator input
and the other at the output improve
the regulator’s stability and transient
response. Microcontroller IC1 also has
two 100nF supply bypass capacitors at
pins 1 and 20.
LED2 lights up when power is applied, with its current limited to around
2-3mA by its 1kW series resistor.
period can be up to 10.9 minutes in
10ms steps. If the delay period is over
10.9 minutes, then the next two bytes
continue that delay.
This means that the maximum sequence can be up to 107 hours (1182 ÷ 2
× 10.9 minutes). However, as extra bytes
are consumed for each solenoid strike,
the practical maximum is somewhat
less than that.
For a more realistic calculation, say
that a recording consists of a series of
eight strikes, spaced two seconds apart,
with a 10-second delay before the next
little tune.
That consumes 32 bytes (8 × 4 bytes)
for every 24 seconds of recording (7
× 2 seconds + 10 seconds). The 1182
byte memory can record up to 37
such sequences, for a total recording
or playback time of 888 seconds (or
14.8 minutes).
Typically, you would leave a longer
period between solenoid drive sequences, so the maximum recording (and
hence playback) time will be longer.
There is no need to completely fill the
memory, as during playback, it only
cycles through the number of bytes that
were recorded in memory
This PCB has five high power MOSFETs
in positions Q2-Q10 with seven lowerpower transistors in Q11-Q23. The
reason (and difference) is explained in
the text. The PCB mounts
in the case without screws
– it simply clips into the
slots on the side guides.
As yet, the holes are not
drilled into the lid for
the on/off switch nor
LED – these can be
done using the front
panel artwork as a
template. We’ll
look at this in more
detail next month.
PCB assembly
The Electronic Wind Chime circuit is
built on a PCB coded 23011201 which
measures 147 x 87.5mm and is available from the PE PCB Service – see
Fig.5. This fits into a UB1 Jiffy box.
Which parts you install depends to
some extent on the number of solenoids
you will use and the solenoid sizes. See
the accompanying panel on this topic.
The parts list specifies the parts
required to drive the maximum 12
solenoids. Asterisks indicate which
parts you can buy fewer of if you plan
to drive a smaller number of solenoids.
This includes S1-S12, R1-R12, the 10kW
pull-down resistors, Q1-Q24, D1-D12
and CON1-CON6.
CON1 and CON6 are three-way
terminal blocks, with two terminals
for a pair of solenoids plus a common
positive connection for each set of six.
CON2-CON5 are two-way terminal
blocks which do not have the common
positive connection, only the negative
connections for two solenoids. So if you
have an odd number of solenoids, you
will end up with an unused terminal in
one of the connectors.
You can have a mix of low- and highcurrent solenoid drivers. Say you might
wish to control two wind chimes, with
each having three large chimes and three
smaller ones.
You could fit MOSFETs at the evennumbered positions (Q4, Q8, Q12...) and
corresponding 100W gate resistors. You’d
then fit transistors at the odd-numbered
34
Practical Electronics | February | 2022
Power supply
12V power for the circuit is applied at
CON7. This flows to the solenoids via
fuse F1. This supply is bypassed with
Memory storage
Twelve bytes of the Flash memory are
dedicated to storing the PWM duty cycle
and on-period parameters for each solenoid (ie, one byte per solenoid).
1182 bytes of Flash memory are used
for storing the playback sequence. Two
bytes of memory are used to record
which solenoid(s) to activate, followed
by a two-byte delay period. Each delay
Fig.5: circuit
board assembly is
straightforward;
simply install the
components as shown
here. Small rectangles
are provided above
the manual control
switches so you can
write the musical
note produced by that
switch, or a solenoid
number. During
construction, take care
with the orientations
of the diodes, ICs,
transistors, terminal
blocks and electrolytic
capacitors.
Q position (Q1, Q5,
Q9...) with 2.2kW base
resistors, for the smaller
chimes. Do not install
both a MOSFET and
bipolar transistor in the
same position.
This complicates
construction a little, but
you can save quite a bit
of money as the bipolar
transistors cost far less
than the MOSFETs.
Start by fitting the
resistors on the PCB
where shown (remember to vary the R1-R12
as described above). It’s
always best to check the
values with a digital
multimeter (DMM) set
to measure resistance.
Continuing on, install diodes D1 to D12
(or as many as required)
and D13. Make sure that
the cathode stripes face
toward the top of the
PCB as shown. Also fit D14 now, which
faces the opposite direction compared
to the others, and is the largest diode.
Then mount switches S1-S12
(where used) and S13. These will
only fit onto the PCB the right way,
so if the switch does not seem to fit,
try rotating it by 90°.
We recommend that IC1 is installed
using a socket. Make sure the end notch
faces toward the left edge of the PCB.
The trimpots can be installed next.
VR1 is the 10kW trimpot that may be
marked as ‘103’ rather than ‘10k’. VR2
is 500kW and may be marked as ‘504’
rather than ‘500k’.
Now mount the fuse clips, making
make sure these are installed with the
correct orientation, ie, with the end
stops toward the outside of the fuse. It
is a good idea to insert the fuse before
soldering the clips to ensure the fuse is
Practical Electronics | February | 2022
SILICON CHIP
aligned within the clips, and that the
clips are oriented correctly.
PC stakes can also be installed at
GND and TP1. However, these can
be left out, and multimeter probes
pressed directly onto the pads for
voltage measurements.
Fit the two-way headers for JP1 and
JP2 next, then the DC socket (CON7).
Follow with the 3-way and 2-way screw
terminals (as many as needed), with the
wire entry holes towards the lower edge
of the PCB.
Now mount the capacitors, noting
that the electrolytic capacitors must be
oriented correctly, with the longer positive leads through the holes marked ‘+’.
Transistors
It is now time to fit the transistors and/
or MOSFETs (along with regulator
REG1), noting again that which ones
and how many you install depends
on what solenoids you are using, and
how many.
The power switch (S14) and the two
LEDs can be mounted in one of two
ways: either directly on the PCB or onto
the lid of the box, with wires making the
connections between the component
and PCB.
We opted to mount the switch and
LEDs on the PCB – this way, they will
not be seen or accessible once the lid
of the box is in place, but that’s OK
as they are mainly used during setup
and recording. Without the power
switch being accessible, the unit can
still be switched on and off via the
12V plugpack.
If you intend to use the LDR to
switch the unit off at night, solder this
in place now. It can be mounted so that
the face of the LDR is toward the back
35
Parts List – E lectronic W ind Ch imes
double-sided plated-through PCB coded 23011201, 147 x 87.5mm
[available from the PE PCB Service]
1 UB1 Jiffy box, 158 x 95 x 53mm
[Jaycar HB6011 (black), Altronics H0201 (black) or H0151 (grey)]
1 12V DC plugpack or similar supply, ideally with 2.5mm ID barrel plug
(current rating dependent on solenoids used, up to 3A maximum)
12* 12V DC spring-return pull solenoids with lever slot [see text]
2* 3-way screw terminals with 5.08mm spacing (CON1,CON6)
4* 2-way screw terminals with 5.08mm spacing (CON2-CON5)
12* SPST momentary switches (S1-S12) [Altronics S1120, Jaycar SP0600]
1 SPST momentary switch (S13) [Altronics S1120, Jaycar SP0600]
1 SPDT toggle switch (S14) [Jaycar ST0335, Altronics S1310]
2 M205 PCB-mount fuse clips (F1)
1 3A M205 fast blow fuse (F1)
1 5A DC PCB-mount 2.5mm ID barrel socket (CON7)
[Jaycar PS0520, Altronics P0621A]
1 20-pin DIL IC socket (for IC1)
1 48kW to 140kW light-dependent resistor (LDR1)
[Jaycar RD3480, Altronics Z1619]
2 2-way pin headers with jumper shunts (JP1,JP2)
2 PC stakes (optional; GND and TP1)
2 or more cable glands for 3-6.5mm cable entry
Choosing solenoids
1
Semiconductors
1 PIC16F1459-I/P 8-bit microcontroller programmed with 2301120A.hex (IC1)
1 7805 1A 5V regulator (REG1)
1 3mm red LED (LED1)
1 3mm green LED (LED2)
* reduce these quantities for driving
12* 1N4004 1A diodes (D1-D12)
fewer than 12 solenoids and note
1 1N4004 1A diode (D13)
that low- and high-current solenoid
1 1N5404 3A diode (D14)
drivers can be mixed and matched
(up to a total of 12)
Capacitors
2 1000µF 16V PC low-ESR electrolytic
2 100µF 16V electrolytic
4 100nF MKT polyester
Resistors (all 1/4W 1% metal film
(Code brown black black orange brown)
1 100kW
12* 10kW (S1-S12 pull-down resistors)
(Code brown black black red brown)
2 10kW
(Code brown black black red brown)
2 1kW
(Code brown black black brown brown)
1 500kW miniature horizontal trim pot, Bourns 3386P style (VR2) (Code 504)
1 10kW miniature horizontal trim pot, Bourns 3386P style (VR1) (Code 103)
Parts for highcurrent solenoid driv ers (>500m A )
12* STP16NF06L, STP60NF06L or CSD18534KCS 60V, 16/60/73A logic-level
N-channel MOSFETs (Q2,Q4,Q6...Q24)
[Jaycar ZT2277]
12* 100W 1/4W 1% metal film resistors (R1-R12) (Code brown black black black brown)
Parts for low - current solenoid driv ers (<500m A )
12* BC337 NPN 500mA transistors (Q1,Q3,Q5...Q23)
12* 2.2kW 1/4W 1% metal film resistors (R1-R12) (Code red red black brown brown)
Miscellaneous
Suitable exterior board or timber, aluminium sheet, wire loom, cable ties, wire,
screws, paint, string
edge of the PCB (by bending the leads),
so it is exposed to the outside light via
a hole in the side of the enclosure. If
you don’t need the LDR feature, link
it out or place a shorting block over
jumper JP2.
Housing
The PCB is held in the plastic case by
the integral clips holding the sides of
the PCB.
36
You will need to drill holes in the
box for the DC socket and the solenoid
wiring. We recommend that this wiring
passes through several cable glands
before being connected to CON1-CON6.
The 9mm hole for the DC socket is
21mm above the outside base of the case
and 26mm in from the outer edge. Cable
glands can be placed 15mm down from
the top edge of the enclosure, adjacent
to the screw connectors CON1-CON6.
The circuit has been designed to cater
for many types of solenoids. We used
D-frame spring-return pull types,
although push-pull types can also be
used. The sizes available range from
miniature through to heavy-duty types
that can draw up to 3A.
What you need depends on the size
of the wind chime you are using. There
are several specifications you need
to look for; for example, the circuit
requires 12V solenoids. Another important specification is the movement
length, or stroke.
Other useful features are a means to
attach to the solenoid plunger. Some
will have holes in the plunger, but others will not have any means to attach
anything to the solenoid plunger.
For small wind chimes, a solenoid
stroke of 4mm might be sufficient,
but for larger chimes, something like
12mm is required.
For use with mini wind chimes
(tubes around 6.35mm in diameter)
and using a direct solenoid plunger hit
to an inline set of chimes as shown
in Fig.2, a push-pull solenoid with a
frame section that measures 21 x 11 x
10mm having a 4mm stroke would be
suitable. Their overall length is 30mm,
and they draw 120mA at 12V DC.
The solenoids for the wind chime
we used have a 30 x 16 x 14mm
frame section and 10mm stroke. Their
overall length is 55mm. The plunger
includes a mounting slot and securing
hole suitable for a lever attachment.
At 12V DC, they draw 2A. The initial
pull is 300g with an ultimate retention
force of 3kg when fully closed.
Both Jaycar and Altronics sell suitable solenoids, and many others are
available via on-line marketplaces
such as eBay.
Next month
The electronics section is virtually complete, but we still need to describe how
to modify your wind chime to add the
solenoids, plus the testing, setup and
sequences recording procedures. All that
will all be covered in next month’s article.
Reproduced by arrangement with
SILICON CHIP magazine 2022.
www.siliconchip.com.au
Practical Electronics | February | 2022
