This is only a preview of the February 2013 issue of Silicon Chip. You can view 19 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "High Performance CLASSiC DAC; Pt.1":
Items relevant to "Do-It-Yourself Seismograph With Tsunami Alarm":
Items relevant to "Mobile Phone Loud Ringer":
Items relevant to "Improved Jacob's Ladder":
Items relevant to "Accurate GPS 1pps Timebase For Frequency Counters":
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Ever missed an important call because
you and your mobile were separated?
Here’s the SILICON CHIP solution!
Mobile
Phone
LOUD
RINGER!
by John Clarke
You know the scene: you’re working outside and the mobile is inside.
Or maybe you’ve left it in the work ute while you’re at a job. Either
way, you pick up the phone and all you see is “missed calls”. Rats!
S
ure, they could have left a message (but many people
don't like doing that). Either way, you now have to
return the call (at your cost!) and the odds are it's someone trying to flog you something you don’t want, someone
who wanted you to do a job but has gone elsewhere in the
meantime, someone seeking a donation to a worthy cause,
or even a wrong number.
Whatever it is, it’s an inconvenience. And an expense.
Wouldn’t it be nice if you could hear the phone ring ’cos
it's now REALLY LOUD? Yes it would be!
We can’t change the ring volume on your phone itself
but we can help you out by adding a mobile phone ring
“extender”.
This simple device picks up the vibration of the mobile
phone ringing (and pretty well all mobile phones have
this feature so you can “feel” the phone ringing in a noisy
environment) and uses that vibration to trigger a loud piezo
siren that you can position wherever you like.
The vibrating alert on a mobile phone typically produces
a 150-180Hz “buzz”. It’s produced by a small electric motor
38 Silicon Chip
running at around 10,000rpm that rotates an eccentric (or
off balance) mass on its shaft.
The Mobile Phone Ring Extender (let's call it the MPRE
for short) is housed in a small case. The idea is that when
you don’t want the phone in your pocket or even close by,
you place it on top of the MPRE case.
The MPRE then provides a (very!) loud phone ring alert
that allows you to get to the phone and hopefully answer
it before it stops ringing.
How it works
Fig.1 shows the general arrangement. A piezo transducer
is the sensor that detects the vibration from the phone.
The vibration from the phone is transferred to the case lid
and that movement is further transferred to the piezo element via an actuator made from a short length of Nylon or
polycarbonate M4 thread, cut from a screw.
Signal from the piezo transducer is amplified and converted to a DC voltage. This DC voltage is monitored using
a comparator that compares the voltage against a reference
siliconchip.com.au
AMPLIFIER
COMPARATOR
AC TO DC
CONVERTER
ACTUATOR
(IC1a)
INTEGRATOR
(D5,VR2)
(D3, D4)
(IC2, VR3)
(IC1b, VR1)
PIEZO
TRANSDUCER
REFERENCE
VOLTAGE
CASE LID
Fig.1: the basic arrangement of our Mobile Phone Ring
Extender. A piezo transducer is mechanically connected
to the case lid which vibrates when the phone vibrates.
This signal is rectified and if high enough, causes two
oscillators to function – the output of these is fed via a
small driver into a piezo siren.
voltage. With no signal, the DC voltage is below the reference and the comparator output is low (near to the ground
supply). With vibration detected, the DC voltage rises above
the reference voltage and the comparator output goes high
(towards the positive supply).
The following circuitry forms a delay circuit whereby the
high level is integrated over time. This integrator is included
so that brief vibrations – such as the phone bouncing to
footsteps – are not sufficiently long enough to be detected
by the following Schmitt trigger (IC2c).
Only longer periods of vibration that really do mean
there’s an incoming call are detected. The integrator delay
is adjustable with VR2 so that the time period can be set
correctly; that is, not too short to detect the placing of the
phone onto the MPRE case but not too long so as to signifi-
SCHMITT TRIGGER
& MODULATION
OSCILLATOR
VOLUME
VR4
DETECT
LED
(LED2)
DRIVER
(Q1)
PIEZO
SIREN
cantly delay the detection to an incoming call.
The Schmitt trigger is a part of the modulation oscillator
and starts oscillation with sufficient signal from the integrator. The detect LED driven from IC2b visually indicates the
detection of an incoming call. IC2b in turn drives IC2d and
IC2a respectively and allows the modulation oscillator to
switch the tone on and off. Modulation rate is adjustable
using VR3.
Output drive from IC2a is adjustable with VR4 and the
wiper voltage is buffered with voltage follower Q1 to drive
the external piezo siren.
Circuit
Circuitry for the MPRE is mainly based on just two ICs,
a dual op amp (IC1) and a quad Schmitt trigger NAND gate
Here’s how it works: simply
place your mobile phone
on top of the Mobile Phone
Ring Extender (with vibrate
turned on). The unit detects
the vibration from incoming
calls and sounds the piezo
siren at right. The siren
shown is one of several
options; more information is
in the text.
siliconchip.com.au
February 2013 39
+8.8V
IC1: LM358
PIEZO
TRANSDUCER
5
SIG
7
IC1b
6
A
VR1 500k
2
100nF
D3
47k
8
3
K
K
GND
1M
D4
100nF
IC1a
VR2 100k
D5
1
A
K
4
1M
10F
1M
A
100nF
AC TO DC
CONVERTER
AMPLIFIER
22k
36k
+4.4V
COMPARATOR
INTEGRATOR
+950mV
10k
10F
+8.8V
8
IC2c
5
10
9
13
4
6
3.3k
VR3 500k
1F
A
10F
IC2a
IC2d
IC2b
MODULATION
11
2
12
DETECT
LED1
1
14
3
7
VOLUME
1k
VR4
10k
Q1
BC337
100nF
C
B
47
E
IC2: 4093B
–
330
K
CON1
9V DC
PLUGPACK
INPUT
+
OUTPUT
TO
PIEZO
CON2 BUZZER
S1
A
K
D1
1N4004
+8.8V
K
A
POWER
D2
1N5819
CON1: 2.1mm DC POWER SOCKET
CON2: 3.5mm PHONO SOCKET
9V
BATTERY
D3–D5: 1N4148
A
SC
2013
MOBILE PHONE RING EXTENDER
B
1N4004, 1N5819
A
LED
BC337
K
K
E
C
K
A
Fig.2: the circuit is based on two low-cost ICs, a dual op amp (IC1) and a quad Schmitt trigger NAND (IC2). It can be
operated from either a 9V battery or, for longer term operation, a 9V DC plugpack.
(IC2). Fig.2 shows the full circuit.
IC1b is the piezo transducer amplifier. This is biased at
4.4V using a voltage divider comprising a 47kΩ, 36kΩ and
10kΩ resistor string connected across the 8.8V supply. Pin
5 is held at this 4.4V via the 1MΩ resistor that provides a
high impedance loading for the piezo transducer.
Amplifier gain is set by the 22kΩ resistor connecting to
the 4.4V reference and VR1’s setting. Low frequency roll
off is at 72Hz, due to the 100nF capacitor in series with
the 22kΩ resistor.
The amplifier mainly amplifies signal above 72Hz and
does not amplify a DC signal. Gain is variable from 1-23.7,
with VR1 set between zero ohms to 500kΩ respectively.
Output from IC1b is rectified using diodes D3 and D4.
The 100nF coupling capacitor at IC1b’s output only allows
AC signal to pass and the signal is clamped at about 0.7V
below 0V by diode D3. Positive signal passes through diode
D4 and is filtered with a 100nF capacitor. The 1MΩ resistor
discharges the capacitor over a 100ms period.
IC1a is the comparator that monitors the filtered DC
40 Silicon Chip
voltage at the non-inverting input (pin 3) and compares
this against the 950mV reference voltage at the inverting
input (pin 2). The 950mV is derived from the same voltage
divider that produced the 4.4V, only from the lower tapping across the 10kΩ resistor. With the pin 3 input lower
than 950mV, IC1a’s output is low, at near to 0V. When pin
3 voltage rises above 950mV, then IC1a’s output goes high,
at close to the 8.8V supply.
This high output from IC1a charges the 10µF capacitor via
diode D5 and the resistance set by VR2. When IC1a’s output
is low, the 10µF capacitor discharges via the 1MΩ resistor.
When the 10μF capacitor is discharged, the pin 8 input
to IC2c is low and the output at pin 10 remains high, because the NAND gate output will only go low when both
the pin 8 and pin 9 inputs are high. The 1μF capacitor at
the second input at pin 9 is charged to a high level via
VR3. IC2b inverts this high to a low output at pin 4 and so
IC2d’s output also remains with its output (pin 11) high.
IC2a inverts this high so that its pin 3 output sits low and
there is no drive to the piezo siren.
siliconchip.com.au
Here’s what it looks like fully assembled, with the end-on
view above showing the minimal controls. We used a
“remote control” case because it already has provision for
an internal 9V battery (battery and output sockets are on
the side of the case in purpose-cut holes).
Upon detection of a vibration signal (and the IC1a output
going high), the resulting high at pin 8 of IC2c’s input allows the modulation oscillator to run. IC2c’s output goes
low and discharges the 1µF capacitor via VR3 whereupon
IC2c’s output goes high again to recharge the 1µF capacitor
via VR3. This cycle repeats.
The input threshold for the NAND gate includes hyster-
esis that is internally provided within IC2.
Each time IC2c’s output is low, IC2b’s output is high and
this also drives the detect LED via a 3.3kΩ resistor. The LED
switches on and off at the modulation rate. IC2d buffers
the modulation signal from IC2b while IC2a inverts the
logic level again and applies the signal across the volume
potentiometer (VR4). The output at the wiper drives the
base of the emitter follower Q1. When the base voltage
goes high, the emitter of Q1 supplies power to the piezo
siren via CON2. A 330Ω resistor is included in series with
the volume control (VR4) to reduce the “dead area” at the
full anticlockwise pot travel where there is no volume.
The wiper voltage for VR4 needs to go above about 0.6V
for Q1 to switch on.
The 330Ω resistor sets the wiper voltage at 268mV when
IC2d’s output is high and the wiper is set fully anticlockwise. Without this resistor, the wiper voltage would be 0V
and would require more clockwise travel before sound is
heard from the siren.
Power for the MPRE can be either from a 9V battery or
a DC supply such as from a 9V plugpack. The 9V battery
supply is via Schottky diode D2 providing reverse polarity
connection protection for the circuitry with minimal voltage drop. Whenever power is connected via the DC socket,
the battery is automatically disconnected. Both supplies
are isolated from each other by the diodes.
With the 0.2V drop across diode D2, the rail voltage with
a fresh battery is very close to 8.8V, as shown on the circuit
diagram. It is usually a little higher from a plugpack because
even though branded “9V”, the output from these can be
(and usually is) anywhere up to about 12V at low currents.
Why detect the vibration ?
Why have we gone to the trouble of detecting the vibration of the mobile phone? Why not simply detect the
ring of the phone, say via a microphone, and use that to
trigger the siren?
The reason is pretty simple: there are so many ring
tones, so many tunes and so many variations on a theme
in mobile phones that it was difficult to create a “one size
fits all” detector; one that would work with everything.
And there was a second problem: how sensitive do you
make it, so that it reliably triggers with a ring but doesn’t
false trigger when the dog barks?
Just about everyone has their vibration alert turned on
all the time – even if the ringer itself is turned off (and that
siliconchip.com.au
was another problem!). So the vibration detector was the
way to go – reliable, worked with all phones, etc.
Believe it or not, we tried yet another method of detection
based on RF. You know how the phone’s handshaking (beep
beep, beepity beep beep) gets into everything?
We thought this would be a great way to detect an incoming call even though mobile phone transmitter power
varies significantly with distance to the cell tower.
But again, we couldn’t make it reliable with all brands
of phone – and it even had more problems detecting 3G
calls than it did 2G. 4G? Don’t know – none of us has a
4G phone!
So we figured detecting the vibration was the best option!
February 2013 41
DETECT
LED
330
A
100nF
Mobile Phone
Ring Extender
1k
S1
K
3.3k
VR4 10k
100nF
PIEZO SIREN
D3
D2
1N5819
D1
1N4004
4004
22k
IC1
LM358
10k
4148
CON2
100nF
1M
D3-D5: 1N4148
10F
+
–
100nF
36k
D4
47
500k
1M
47k
100k
B
Q1
10F
VR1
4148
C 2013
D5
4148
E
1F
VR3
500k
10F
VR2
IC2 4093
C
BC337
1M
GND SIG
TO 9V
BATTERY CLIP
+
–
CON1
THREAD THROUGH HOLES
FOR STRAIN RELIEF
PIEZO
TRANSDUCER
MOUNTS ABOVE
OTHER
COMPONENTS
ON PCB
9V DC
PLUGPACK
SUPPLY
+
–
Fig.3 (above): the same-size PCB component
overlay, with an early prototype photo alongside
(some components have been changed since the
photo was taken). While the electrolytic capacitors are shown above in traditional position, the
photo at right shows that these are all “laid
over” to give room for the case lid to fit. Also,
the two links shown above will only be required
if the PCB is single-sided.
Inset at right is a close-up of the piezo transducer
with a short length of 4mm nylon screw thread,
used to provide a mechanical connection between the
transducer and case lid. It simply relies on touching the
lid; it is not glued in.
“At rest” current consumption is
about 6mA.
Construction
All components for the MPRE are
mounted on a PCB coded 12110121
and measuring 63.5 x 86mm. The
PCB and components are housed in a
“remote control” case measuring 135 x
70 x 24mm. This case is used because
it also houses the 9V battery. A panel
label attaches to the front face of the
case (or, depending on the kit source,
may be supplied already printed).
The PCB is designed to mount onto
the integral mounting bushes within
the box. Make sure the corner edges
of the PCB are shaped to the correct
outline so they fit into the box. They
can be filed to shape if necessary using the PCB outline shape as a guide.
It is rare to find faults with modern
PCBs, but it’s worth checking the PCB
42 Silicon Chip
for breaks or shorts between tracks or
pads. Repair if necessary.
Check the hole sizes for the PCB
mounting holes – they should be 3mm
in diameter.
Assembly can now begin. Start by
the inserting the resistors and use the
resistor colour code table to help in
reading the resistor values. A digital
multimeter can also be used to measure each value – in fact, it’s a good
idea because many colour bands on
resistors look very similar.
If you use a PCB purchased from
the SILICON CHIP Partshop, it will be
double-sided but other PCBs may
be single sided and require two wire
links (above and below IC2) to be
soldered in.
The diodes can now be installed and
being polarised, must be mounted with
the orientation as shown. IC1 should
be mounted directly on the PCB since
there is insufficient room (height wise)
for a socket once the piezo transducer
is installed. IC2 can be mounted on a
socket if desired.
When installing the ICs, take care to
orient them correctly with the notch
(or circle marking pin 1) as shown on
the overlay.
Capacitors can be mounted next.
The electrolytic types must be oriented with the shown polarity and
far enough above the board (~6mm or
so) so that they can be bent over to lie
parallel, or near-parallel, to the surface. Otherwise you will not be able to
put the lid on. This simply means you
need to have sufficient capacitor lead
length to allow each part to bend over.
Trimpots VR1-VR3 can be mounted
next. They’re not all the same – VR2
is 100kΩ (code 104) while the others
are 500kΩ (code 504). Transistor Q1 is
next to install.
siliconchip.com.au
CON1 (DC input socket) and CON2
(3.5mm output to siren) should be
mounted right down on the PCB
surface.
Potentiometer (VR4) and the PCB
mounted switch (S1) can also be fitted.
LED1 and its series 3.3kΩ resistor
can be regarded as optional if you don’t
require a visual indication of detected
ring (leaving them out will also save
a little bit of power if running from a
battery).
If you do fit them, mount LED1 horizontally but at a height of 6mm above
the PCB. Bend its leads at 90°, 7mm
back from the LED body making sure
the anode lead is to the left.
Panel holes
The side of the base of the case needs
to be filed using a rat tailed file to allow
connections to both CON 1 and CON2
through the side the case. Position the
PCB in the base of the case with the
PCB mounting holes aligned with the
mounting pillars. Mark out the socket
positions and file to shape.
A similar shape is required on the
lid and its position is found by placing
the lid onto the base of the case (with
the PCB removed) and filing out the
lid half for a circular hole.
Before securing the PCB in place,
drill out the small front edge panel for
the potentiometer, switch and LED (if
used). A drill guide is available and is
provided with the front panel label.
This can be used as a guide as to the
drill hole positions.
Nuts for the potentiometer and
3.5mm socket are not required. The potentiometer shaft is fitted with a knob
after the front edge panel is placed
over the shaft, switch S1 and the LED.
Wiring
Follow the wiring diagram to make
the connections from the piezo transducer to the PCB. The battery clip
lead is inserted first from within the
the battery compartment before being
looped through the strain relief holes
and attaching to the PCB. Make sure
the polarity is correct with the red battery clip lead as the plus lead.
Piezo transducer
The piezo transducer is raised
above the PCB using two 6.3mm
tapped standoffs. M3 screws secure
the standoffs from the bottom and
the piezo is secured with two more
M3 screws into the standoffs. Note
that the mounting holes in the piezo
transducer mounting lugs will need to
be carefully enlarged with a 3mm (or
1/8”) drill bit.
The wires are attached to the ‘Sig’
and ‘GND’ inputs on the PCB.
An M4 Nylon screw, which provides
the mechanical connection between
the vibrating case lid and the piezo
transducer, is cut so that you have a
4mm long length of thread. The head
of the screw is not used. This length
is inserted into the centre hole of the
piezo transducer.
The length of this screw thread is
important. Too short and it will not
make contact with the lid. Too long
and the lid will not fit onto the case
without excessive bowing.
The PCB is secured to the base of
the case using four M3 x 6mm screws
that screw into the integral mounting
bushes in the box.
Label
As mentioned earlier, some kitset
suppliers are now pre-printing labels
onto their cases, so you won’t have to
do anything.
But if yours is blank, or you’ve assembled your own bits, the panel label
for this project can be downloaded
from the SILICON CHIP website (www.
siliconchip.com.au). When downloaded, you can print onto paper,
Resistor Colour Codes
No.
o 3
o 1
o 1
o 1
o 1
o 1
o 1
o 1
o 1
Value
1MΩ
47kΩ
36kΩ
22kΩ
10kΩ
3.3kΩ
1kΩ
330Ω
47Ω
siliconchip.com.au
4-Band Code (5%)
brown black green gold
yellow violet orange gold
orange blue orange gold
red red orange gold
brown black orange gold
orange orange red gold
brown black red gold
orange orange brown gold
yellow violet black gold
5-Band Code (1%)
brown black black yellow brown
yellow violet black red brown
orange blue black red brown
red red black red brown
brown black black red brown
orange orange black brown brown
brown black black brown brown
orange orange black black brown
yellow violet black gold brown
Parts List –
Mobile Phone
Ring Extender
1 PCB coded 12110121, 63.5 x 86mm
1 panel label 113 x 50mm
1 remote control case 135 x 70 x
24mm (Jaycar HB5610)
1 piezo siren (Jaycar AB-3456,
Altronics S-6127)
1 piezo transducer (Jaycar AB3440,
Altronics S6140)
1 PCB mount SPDT switch (Altronics
S1421 or equivalent) (S1)
1 PCB mount DC socket (Jaycar
PS-0520, Altronics P0621A)
(CON1)
1 3.5mm stereo PCB mount socket
(Jaycar PS-0133, Altronics P0092)
(CON2)
1 3.5mm mono plug [to connect
siren] (Jaycar PP-0144, Altronics
P-0028)
1 knob to suit VR4
1 9V battery, with clip
8 M3 x 5mm screws
2 6.3mm long M3 tapped nylon
spacers
1 M4 polycarbonate or Nylon screw
(cut for a 4mm thread section
without the head)
4 PC stakes (optional at wiring points)
Suitable length polarised figure-8
cable if siren is to be remotely
mounted
Semiconductors
1 LM358 dual op amp (IC1)
1 4093 CMOS quad Schmitt NAND
gate (IC2)
1 1N4004 1A diode (D1)
1 1N5819 Schottky diode (D2)
3 1N4148 switching diodes (D3-D5)
1 BC337 NPN transistor (Q1)
1 3mm high intensity LED (LED1)*
Capacitors
3 10µF 16V PC electrolytic
1 1µF 16V PC electrolytic
4 100nF MKT polyester (code: 104)
Resistors (0.25W, 1%)
3 1MΩ
1 47kΩ
1 36kΩ
1 22kΩ
1 10kΩ
1 3.3kΩ*
1 1kΩ
1 330Ω
1 47Ω
1 100kΩ horizontal mount trimpot
(code 104) (VR2)
2 500kΩ horizontal mount trimpots
(code 504) (VR1,VR3)
1 10k log 9mm potentiometer (Jaycar
RP-8610 or equivalent) (VR5)
* optional (see text)
February 2013 43
Volume
Detect
Power
SILICON CHIP
Output to
Piezo
Siren
Figs. 4 & 5: front
panel artwork for the
Mobile Phone Ring
Extender, and below
right the template for
drilling the end (top)
panel holes. These
images can also be
downloaded from
www.siliconchip.com.
au
it can be more easily heard – outside, for example. In this
case, you’ll need to connect a suitable length of figure-8
polarised cable to the siren and in either case, you’ll need
to solder on a 3.5mm mono plug so that it can plug into
the MPRE. The siren is polarised – the red (+) wire goes
to the centre pin on the 3.5mm plug.
If you do decide to mount the siren outside, you will
need to fit it so it’s protected from the elements – under
an eave, for example.
Within reason, there is no limit (say to a standard suburban house boundary) to the length of wire between the
piezo siren and MPRE.
-
Mobile Phone
Ring Extender
Place phone on this top panel
with “vibrate” turned on
Pot
7mm
.
LED
3mm
+
Switch
5mm
9VDC
Input
End Panel Drill Guide
Testing
sticky-backed photo paper or onto plastic film.
When using clear plastic film (overhead projector film)
you can print the label as a mirror image so that the ink is
behind the film when placed onto the panel. Once the ink
is dry, cut the label to size.
Glue the panel to the lid of the case with silicone sealant, contact adhesive or similar glue. Where you use the
clear film, a contrasting silicone colour can be used such
as white or grey to show up the printing on a black panel.
Clear silicone can be used for non-white panels since the
panel itself will provide the contrast against the printed
label.
Piezo siren
The piezo siren is pretty loud – you might find it loud
enough to mount close to the MPRE via the short length
of cable it comes with.
Or you might prefer to mount the siren elsewhere, where
Another “siren”?
44 Silicon Chip
Initially, don’t connect the siren – it will deafen you
at close range!
When you switch on, using a 9V battery, there should
be around 8.8V between pins 4 & 8 of IC1 and between
pins 7 and 14 of IC2. Pin 2 of IC1 should be about 950mV
above 0V (the GND terminal). Pin 5 of IC1 should be about
4.4V above 0V.
Note that these voltages might differ a little from these
values depending on the supply voltage.
With a plugpack supply they will almost certainly be
higher but still should be in much the same ratio.
Now set VR1, VR2 and VR3 to mid position and attach
the piezo siren.
You should be able to trigger the MPRE into operation
by repetitively tapping the case. That should introduce
sufficient vibration to be detected by the piezo transducer
and you should hear the alert sound and see the detect
LED flash.
You can adjust VR3 and VR4 for the desired sound, with
VR3 adjusting the rate of switching the tone on and off.
Clockwise will increase the frequency.
Final testing is done with a mobile telephone (set to
vibrate). Place the phone on top of the MPRE and make a
call to the phone using another phone.
Again, the MPRE should begin flashing the detect LED
and the siren should sound. If neither happens, adjust
VR1 further clockwise for more sensitivity.
VR2 should be adjusted so that the MPRE does not sound
unless there is an incoming call.
It should not detect a single tapping on the case with
your finger nail. VR2’s adjustment is usually at mid-setting
but may need to be set more anticlockwise to ensure that
an incoming call is detected without too much delay or
more clockwise to prevent detection of single tapping on
SC
the case.
Two piezo sirens have been specified for this project but since building
the prototype, we’ve come across a
possible alternative – albeit not made
for the purpose but nevertheless we
believe would be quite suitable.
By coincidence, Jaycar Electronics advertised a “Water Leakage
Alarm” (Cat LA-5163) in the January issue of SILICON CHIP for just
$9.95 – cheaper than either of the
piezo sirens. We weren’t particu-
larly interested in detecting
water but we were interested in the alarm side.
On opening the case,
we found it very easy
to connect to the two
solder pads which
trigger the alarm.
The photo above shows
the two pads to connect
to (clip off or unsolder the
existing water sensor wires).
TRIGGER
CONNECTIONS
siliconchip.com.au
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