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Component video
to RGB converter
Want the best possible picture quality from
your DVD player? The component video
outputs are the ones to use. But what if
your TV can only accept “RGB” video
signals? This easy-to-build converter solves
the problem, with no discernible picture
degradation.
T
By JIM ROWE
HE PICTURE AND sound quality available from DVD video
discs is streets ahead of what’s
available from VHS tapes. That’s
no doubt why sales of DVD players,
widescreen TVs and surround sound
systems have rocketed ahead in the
last couple of years. DVDs have also
24 Silicon Chip
generated tremendous interest in setting up home theatres, so enthusiasts
can watch movies at home with a
presentation almost as good as that in
their local cinema.
At the same time, the very high
picture and sound quality available
from the best movie DVDs has raised
consumer expectations. And it has motivated enthusiasts to find out how they
can achieve the best possible results
from their home theatre set-ups.
For example, most people are now
aware that the highest picture quality
from a DVD can be achieved only by
using a player fitted with “component
video” outputs, connected in turn to
the corresponding inputs of a widescreen TV or video projector. This is
because the video is actually recorded
on DVDs in digital component format,
so component video output signals
have undergone less processing than
those from S-video or composite video
outputs.
As a result, component video
signals provide cleaner and sharper
pictures than the other signal formats. However, some widescreen
TVs (particularly those of European
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Fig.1: block diagram of the Component Video To RGB Converter. IC1b is used to produce the G-Y colour difference
signal, while IC2a, IC3a & IC4a produce inverted RGB signals which are then buffered and fed to the outputs.
origin) and some projectors don’t have
component video inputs. Instead, they
may be fitted with “RGB” (red, green,
blue) video inputs, made either via
RCA connectors or a European-style
SCART connector – these in addition
to the usual composite video and Svideo inputs
And that’s where problems can arise
– RGB inputs are not compatible with
component video signals (and most
DVD players don’t have RGB outputs).
This means that you need a converter
box to change the signal format if you
want to drive your TV’s RGB inputs
from the component video outputs on
your DVD player.
And that’s exactly what this lowcost project is designed to do. As
shown in the photos, it’s housed in a
small instrument case and has three
RCA sockets on the front panel to accept component video signals from a
DVD player. The circuitry inside then
processes these signals to produce the
corresponding RGB video and sync
signals, which are provided via four
RCA sockets on the rear panel.
These output signals can then be fed
to the RGB video inputs of a TV set or
video projector, either via RCA-to-RCA
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cables or via a SCART adaptor cable
if necessary.
The complete converter is easy to
build and runs from a 9V AC plugpack
supply, drawing less than 150mA
(1.3W).
How it works
To understand how the converter
works, you need to know that the
component video format used on
DVDs consists of three video signals
or “components”. These are the “Y” or
luminance signal and two other signals
called “R-Y” (or “Cr” or “Pr”) and “B-
Y” (or “Cb” or “Pb”). The Y signal is
basically the high-bandwidth black
and white picture information, while
the R-Y and B-Y signals are described
as the colour difference signals (these
have a lower bandwidth than the Y
signal).
As the R-Y and B-Y labels suggest,
these two colour difference signals
actually correspond to the red (R) and
blue (B) colour signals from the colour
TV camera (or film scanner) that’s used
to produce the video signals in the first
place, but with the Y luminance signal
subtracted from them.
The RGB output signals are accessible via RCA sockets at the rear of the
unit, along with a composite sync output signal (see text). Also accessible
from the rear is the power socket.
May 2004 25
Parts List
1 PC board, code 02105041,
117 x 102mm (double sided)
1 plastic instrument case, 140 x
110 x 35mm
7 RCA sockets, 90° PC-mount (2
red, 2 black, 1 yellow, 1 green,
1 white)
1 2.5mm concentric power
socket, PC-mount
8 4G x 6mm self-tapping screws
2 M3 x 6mm machine screws
with nuts & lock washers
4 stick-on rubber feet
Semiconductors
4 MAX4451ESA dual wideband
op amps, SOIC-8 (IC1-IC4)
1 LM1881 video sync separator
(IC5)
1 7805 +5V regulator (REG1)
1 7905 -5V regulator (REG2)
1 3mm green LED (LED1)
2 1N4004 diodes (D1,D2)
Capacitors
2 2200µF 16V or 25V RB electrolytic
2 100µF 10V RB electrolytic
2 10µF tantalum
2 2.2µF tantalum
9 100nF multilayer monolithic
2 100nF MKT polyester
1 470pF disc ceramic
Resistors (0.25W, 1%)
1 680kΩ
19 510Ω
1 7.5kΩ
1 470Ω
1 4.3kΩ
1 180Ω
1 3.6kΩ
1 100Ω
1 2.7kΩ
1 91Ω
1 1kΩ
4 75Ω
1 620Ω
1 24Ω
If you’re wondering where the green
or “G” colour signal is hiding, it’s inside the Y signal. That’s because the Y
signal is itself produced by processing
or “matrixing” the three original colour camera signals, according to this
standard formula:
(1). Y = 0.3R + 0.59G + 0.11B
So a more expanded way of expressing the R-Y and B-Y signals is:
(2). R-Y = 0.7R - 0.59G - 0.11B
(3). B-Y = -0.3R - 0.59G + 0.89B
Now since the two colour difference
component signals simply consist of
the Y “mixture” signal subtracted from
the original R and B signals, it’s not
very difficult to convert them back
26 Silicon Chip
again. All that needs to be done is to
add the Y signal to them again; ie:
(4). R-Y + Y = R
(5). B-Y + Y = B
It’s slightly harder to restore the
original green signal, because this
involves two steps. First we have to
recreate the G-Y signal and this is done
by dematrixing the R-Y and B-Y signals
according to this expression:
(6). -(0.51(R-Y) + 0.186(B-Y)) = G-Y
You can check this out for yourself
by expanding the lefthand side using
the full expressions for R-Y and B-Y
given in equations (2) and (3). The G
signal can then be recovered by adding
in the Y signal, as follows:
(7). G-Y + Y = G
Block diagram
Just how we do all of this is shown
in the block diagram of Fig.1.
The first step is to reconstruct the
G-Y signal, by combining 0.51 of the
R-Y signal with 0.186 of the B-Y signal.
This is done using a wideband inverting adder stage based on IC1b. We now
have all three colour difference signals
(the other two are fed in directly from
the DVD player), so these are then
added to the Y luminance signal using inverting adder stages IC4a, IC3a
and IC2a.
The outputs of these stages are thus
inverted versions of the R, G and B
colour signals, so all we have to do
after that is pass each one through an
inverting output buffer. These output
buffers – IC4b, IC3b & IC2b – then drive
75Ω video cables and the 75Ω inputs
of a TV receiver (or video projector).
Note that each output buffer stage
has a 75Ω “back termination” resistor
in series with the output. Because of
this, each buffer is given a voltage gain
of two (+6dB), to compensate for the
6dB loss that is introduced by these
resistors.
But why does the converter also
have a sync separator stage using IC5?
Well, we’ve included this because
there’s some variation in the way TVs
and video projectors with RGB inputs
handle the video sync signal. Some
extract the sync signal from the green
(G) video signal, a technique known
as “sync out of green”, while others
expect to receive the video sync signal
via a separate composite sync (CS)
input line.
The green output from the converter
automatically contains the sync signals (as do the red and blue signals),
so there’s no trouble driving a set with
“sync out of green” circuitry. However,
so that you can also drive a set which
needs separate composite sync, we’ve
included the sync separator as well.
This is derived by first feeding the Y
signal to a low-pass filter to remove the
colour information. The signal is then
fed to a sync separator stage based on
IC5 and the CS output from this stage
then fed through unity gain buffer
stage IC1a, so that the sync signal can
be fed along a 75Ω cable.
Circuit details
If you’ve followed the description
so far from the block diagram, you
shouldn’t have any problems following the full circuit – see Fig.2.
As shown, all the video adder and
output buffer stages are designed
around MAX4451ESA dual wideband
(210MHz) op amp ICs from Maxim
Integrated Products.
Despite its low cost, the MAX4451
is a very impressive device. Each of its
two op amps has a -3dB bandwidth of
210MHz, a gain flat to 55MHz within
0.1dB, and an output slew rate of
485V/µs. This is in a device which
comes in an 8-lead SOIC package,
and draws a quiescent current of just
6.5mA per amplifier from a ±5V supply. In short, it is ideal for this type of
video processing circuit.
The nominal resistor value shown
as R1 in the block diagram becomes
510Ω in the full circuit, so this is the
value of most of the resistors in the
converter. The main resistors with
different values are the input resistors
for IC1b – which are values chosen to
give the correct fractions of R-Y and
B-Y to reconstruct G-Y – and the load
resistors for the R-Y, Y and B-Y inputs.
These may seem to have rather strange
values but they’ve been chosen to bring
each input resistance as close as possible to 75Ω (for good cable termination) while allowing for the inputs of
the various adder circuits.
The back termination resistors for
each of the four converter outputs are
of course 75Ω, as shown in the block
diagram. Note that although sync output buffer IC1a is a unity gain “voltage
follower”, the MAX4451 requires a
24Ω resistor in series with the link
back to the negative input to ensure
stability.
The low-pass filter that’s used to
remove the colour information (prior
to the sync separator stage) consists of
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May 2004 27
Fig.2: the complete circuit if the Component Video To RGB Converter. The video adder and output buffer stages are all based on MAX4451 dual wideband op
amps, while an LM1881 sync separator is used to provide the sync output (via buffer IC1a).
from +5V and -5V, while the LM1881
also runs from +5V. This allows the
converter to be operated from a very
simple power supply.
As shown, this supply uses an external 9V AC plugpack and this feeds two
half-wave rectifiers (D1 & D2) and two
2200µF capacitors to give ±13.5V DC
rails. Regulators REG1 and REG2 are
then used to provide stable ±5V rails
for the converter circuitry. In addition,
the +5V rail is used to power the green
pilot LED via a 470Ω current-limiting
resistor.
Construction
All the video converter circuitry
is built on a double-sided PC board
coded 02105041 and measuring 117
x 102mm. This in turn is housed in
a small instrument case measuring
140 x 110 x 35mm, to produce a very
compact and neat unit.
There’s no off-board wiring at all,
because all the input and output
connectors are mounted directly on
the PC board along the front and rear
edges. As a result, they are all accessed
through holes in the front and rear
panels, when the case is assembled.
Note, however, that although the
PC board is double-sided, the board
supplied in kits will probably not have
plated-through holes (unless one of
the kit suppliers decides to provide
it in this more expensive form). As a
result, you’ll need to solder many of
the component leads to the copper on
the top of the board, as well as underneath. You’ll also need to solder short
lengths of tinned copper wire (such as
resistor lead offcuts) through a small
NOTE: RED DOTS INDICATE WHERE COMPONENT
LEADS AND PIN-THROUGHS ARE SOLDERED TO
BOTH THE TOP AND BOTTOM COPPER
Fig.3: install the parts on the top of the PC board as shown here. The red dots
indicate where component leads and “pin-throughs” have to be soldered on
both sides of the board.
a 620Ω resistor and 470pF capacitor.
From there, the signal is fed to pin 2
of the sync separator (IC5) via a 100nF
capacitor. A standard LM1881 device
is used for the sync separator and its
output at pin 1 is fed to pin 3 of the
unity-gain output buffer (IC1a).
Power supply
All the MAX4451 amplifiers run
Table 1: Resistor Colour Codes
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
No.
1
1
1
1
1
1
1
19
1
1
1
1
4
1
28 Silicon Chip
Value
680kΩ
7.5kΩ
4.3kΩ
3.6kΩ
2.7kΩ
1kΩ
620Ω
510Ω
470Ω
180Ω
100Ω
91Ω
75Ω
24Ω
4-Band Code (1%)
blue grey yellow brown
violet green red brown
yellow orange red brown
orange blue red brown
red violet red brown
brown black red brown
blue red brown brown
green brown brown brown
yellow violet brown brown
brown grey brown brown
brown black brown brown
white brown black brown
violet green black brown
red yellow black brown
5-Band Code (1%)
blue grey black orange brown
violet green black brown brown
yellow orange black brown brown
orange blue black brown brown
red violet black brown brown
brown black black brown brown
blue red black black brown
green brown black black brown
yellow violet black black brown
brown grey black black brown
brown black black black brown
white brown black gold brown
violet green black gold brown
red yellow black gold brown
siliconchip.com.au
Will It Work Backwards?
Can this circuit be made to work
backwards – ie, convert RGB video
to component video?
Unfortunately, the answer to this
question is “no”. RGB to component video conversion requires
a PAL encoding circuit, which is
much more complicated than the
relatively simple unit described
here.
number of “via” holes, to make connections between some of the top and
bottom tracks.
These points are all indicated on the
“top-side” PC board overlay diagram
(Fig.3) with red dots.
As shown in Fig.3, most of the components fit on the top of the board in
the usual way. The only exceptions are
the four MAX4451ESA broadband op
amps (IC1-IC4), which are in surfacemount SOIC packages and must be
mounted on the bottom of the board.
Begin the board assembly by fitting
the short wire links which form “vias”
between some of the top and bottom
copper tracks. There are only five of
these, all in the central area of the
board around IC5. Fitting these first
will ensure you don’t forget them!
Next, fit the resistors, making sure
you solder their “earthy” leads on both
sides of the board where indicated.
That done, install the RCA sockets
and the 9V AC input socket, using a
small drill to enlarge their mounting
holes if necessary.
The small monolithic and MKT capacitors, plus the solitary 470pF disc
ceramic, can go in next, followed by
the four TAG tantalum capacitors and
the larger electrolytics. Make sure that
the polarised components are all orientated correctly, as shown on Fig.3,
and don’t forget to solder their leads
to the top copper as well where this
is indicated.
Next, fit the two diodes in the power
supply (D1 & D2), again watching their
polarity. Follow these with the two
regulators, making sure that you fit
each one in the correct position. REG2
is the 7905 and goes on the lefthand
side; REG1 is the 7805 and mounts to
the right of REG2.
Note that both regulators are mounted horizontally on the top of the board,
with all three leads bent downwards
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This view shows the fully assembled PC board. Be sure to use the “correctcolour” RCA socket (or a near equivalent) at each location, so that you can
easily identify their functions.
Fig.4: the four MAX4451 dual op amps are soldered to the underside of the PC
board as shown here. Make sure you install them the correct way around.
May 2004 29
5mm from the body so that they pass
down through the board holes. Their
device tabs are then fastened against
the board’s top copper using 6mm x
M3 machine screws and nuts.
Once the regulators have been fitted, the next step is to install IC5, the
LM1881 sync separator chip. This
comes in an 8-pin DIL package and
mounts on the top of the board in the
usual way. Take care with its orientation, though, and note that its earth
pin (pin 4) is soldered to the copper
on the top of the board as well as
underneath.
Fitting the surface-mount ICs
Use a fine-tipped soldering iron when installing the four MAX4451 dual op
amps on the underside of the board. Once they’re in, check your work carefully
using a magnifying glass, to ensure there are no solder bridges.
You should now be ready to fit the
four surface-mount ICs (IC1-IC4),
which are the only parts mounted under the board. These are in an 8-lead
SOIC package, with 1.25mm lead
spacing – so they’re not too small for
manual handling and soldering, provided you’re careful and use a soldering iron with a fine-tipped bit.
To fit these ICs, invert the board and
find the four mounting locations using
the underside diagram as a guide – see
Fig.4. You’ll find two sets of four small
The PC board is secured inside the case using eight 6mm-long self-tapping
screws – four along the front edge and four along the rear.
30 Silicon Chip
siliconchip.com.au
rectangular pads in each position. That
done, remove the four devices from
their packaging and examine each one
with a magnifying glass so that you can
identify the small chamfer along one
side – this is used to identify pins 1-4
of the device.
All four devices are mounted on
the board with this chamfered side
towards the front – ie, downwards
in Fig.4.
Each device is installed by first placing it on its set of pads (with the correct
orientation) and holding it there using
a vacuum pick-up tool or toothpick
while you press down gently on one
of its eight leads with the tip of your
soldering iron. This will usually make
a weak solder joint between the lead
and the tinning on the board copper
– enough to hold the device in place
while you solder the rest of its leads to
their pads. That done, you can then go
back and solder the first lead properly,
to complete the job.
Completing the PC board
The final component to fit is the
power LED (LED1). This fits from the
top of the board, with its longer anode
lead towards the right (ie, towards
CON1). Solder the leads in place with
the body of the LED about 17mm above
the top of the board (a strip of cardboard makes a handy spacer).
Bend both leads down together at
right angles after soldering, at a point
9mm above the board (ie, 8mm from
the LED body). The LED will then be
pointing forward horizontally, ready to
protrude through the matching hole in
the front panel when it is fitted.
Fig.5: this is the full-size etching pattern for the top side of the PC board.
Drilling the panels
At this stage, your converter board
assembly should be complete, so place
it aside while you prepare the front
and rear panels of the case. These
each involve drilling and reaming a
small number of holes for the various connectors and the LED, using a
photocopy of the panel artwork as a
drilling guide.
Additional photocopies of the artworks can then be cut out and attached
to the outside of each panel, to make
them look professional, as on the
prototype.
The way to do this is to first make
a copy of the artwork on adhesivebacked “A4 label sheet” paper. The
labels are then trimmed, peeled off the
backing and attached to the panels. A
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Fig.6: the full-size etching pattern for the bottom of the PC board. Check both
sides of the PC board for etching defects before installing any parts.
length of clear packaging tape (ie, wide
adhesive tape) is then applied over
each panel, to protect it from dirt and
finger grease.
Finally, the excess tape can be
trimmed off around the panels and
the holes cut out using a sharp hobby
knife.
May 2004 31
Fig.7: these full-size artworks can be used as drilling templates for the front and rear panels.
Of course, if you buy a complete
kit, you probably won’t have to do
any of this. Instead, the panels will
most likely be supplied pre-punched
and with screened lettering for a really
professional finish.
Now for the final assembly. This is
done by first fitting the panels over the
connectors on each side of the board
(and over the LED in the case of the
front panel) and then lowering this
assembly into the bottom half of the
case – ie, by sliding each panel into its
mating slot. It’s then simply a matter
of fitting eight small 6mm long selftapping screws (four along the front
edge and four along the rear) to hold
the PC board in place.
Finally, the top half of the case can
be fitted and secured from the bottom
using the two long countersink-head
self-tappers provided.
Your Component Video To RGB
Converter should now be complete
and ready for use. There are no adjustments to make – all you have to do is
connect a suitable 9V AC plugpack
and it should spring to life.
Troubleshooting
If it doesn’t work, the first step is
to go back over your work and check
that all components are correctly positioned and orientated. Check also for
missed solder joints, especially where
leads have to be soldered on both sides
of the PC board.
Next, check the power supply rails.
There should be +5V at the output of
REG1 and -5V at the output of REG2.
If you don’t get this, check the two
regulators and diodes D1 and D2.
You should also be able to measure +5V (with respect to ground)
on pin 8 of all ICs and -5V on pin 4
of IC1-IC4.
Finally, if LED1 fails to light and the
+5V rail is correct, check that the LED
has been installed correctly. Check
also that its 470Ω current limiting
SC
resistor is correct.
Car Projects, Volume 2
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Control; LED Lighting For Cars; The Booze Buster Breath Tester; Little
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