This is only a preview of the April 1997 issue of Silicon Chip. You can view 25 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 "Build A TV Picture-In-Picture (PIP) Unit":
Articles in this series:
Items relevant to "A Digital Voltmeter For Your Car":
Articles in this series:
Items relevant to "Loudspeaker Protector For Stereo Amplifiers":
Items relevant to "Train Controller For Model Railway Layouts":
Articles in this series:
Purchase a printed copy of this issue for $10.00. |
By JOHN CLARKE
Watch two TV channels at once!
If you want to watch two TV channels at once, this
Picture-in-Picture unit will come in handy. It will
enable you to check on the golf, cricket or your
second favourite show while also watching another
channel. It’s easy to build and all functions are
infrared remote controlled.
TV Picture-in10 Silicon Chip
H
OW MANY times have you
wanted to see what is happening on a second TV channel
while watching another program?
It may be that the program that you
want to watch next starts before the
present one is finished or there are
two programs that you want to see
but they are showing at the same time.
You may also want to watch another
channel while the advertisements
are on but not want to miss the show
when it comes back on. With this
Picture-in-Picture unit you can do all
those things and more.
Picture-in-picture or PIP on a tele
vision screen means that there is a second small picture of another channel
superimposed on the main picture. It
is usually about 1/6th the size of the
screen and so it does not normally
detract too seriously from the main
program. If it does cause problems, it
can either quickly be switched off or
“flicked” (using the ROTATE button)
to another corner of the screen.
You can also quickly swap the
PIP with the main picture,
just by pressing the SWAP
button on the remote
control. When this is
done, the original PIP is
viewed full size, while
the original full-sized
program is shrunk to the
smaller PIP area. The sound
is automatically swapped with
the picture.
Note that you can also swap the
sound from one channel to the other,
so that either the main or PIP channel
can be heard.
Another very useful feature is a
sound muting facility. This is particularly handy for advertisements which
are usually at a louder volume than
normal program material.
As shown in the photos, the TV
Picture-In-Picture Unit is housed in
a slimline plastic case with terminals
at the rear for the audio and video
connections. On the front is the power
switch, a power indicator LED and
a window for the infrared remote
control sensor. The handheld remote
control takes care of all functions,
except for power on/off switching.
To make the construction easy,
the PIP unit is based on a pre-built
module which performs all the video functions. We have added in the
audio and remote control facilities to
complete the unit.
What you need
Two video sources are required for
the PIP unit to operate and this would
normally be provided by two video
players. Just about every household
has at least one VCR and many have
two, although often the tape transport
mechanism in the older unit has failed.
Main Features
•
•
•
•
•
•
•
•
•
Adds a small picture (PIP)
of another channel to one
corner of the TV screen
PIP can be displayed in any
corner of the screen
Main picture & PIP can be
swapped at the press of a
button
Audio automatically swaps
with picture swap
Audio signal can be either
for the main picture or for
the PIP
Audio mute facility
Stereo or mono audio
Remote control functions for
all features
Direct video or RF modulator
output (channel 0 or 1)
This handpiece remotely selects all the
functions of the Picture-In-Picture Unit. It
lets you move the PIP to any corner of the
screen, swap between the PIP and the main
picture, and swap and mute the audio.
-Picture Unit
April 1997 11
Don’t do this unless you are experienced with TV/video circuits and
know exactly what you are doing.
Be aware also that some older TV
sets may have a live chassis and that
any modifications will invalidate the
set’s warranty. Add in any technical
difficulties that you may encounter
(signal levels, etc) and you can see
why we recommend the two-VCR
approach.
Fig.1 shows a typical installation
for the PIP Unit. The two VCRs receive
the incoming RF from the antenna via
a splitter and their audio and video
outputs are fed to the PIP Unit. The
RF modulated output from the PIP
unit (channel 0 or 1) is then fed to
the antenna input (RF IN) of the TV
receiver.
Alternatively, the audio and video
outputs from the PIP Unit can be fed
to the TV receiver, provided the set
has provision for these inputs. The
left and right (L & R) audio outputs
can also be fed to a stereo amplifier.
Note that although Fig.1 depicts
stereo VCRs, mono VCRs can also
be used – just use mono cables and
connect to either the left or right audio
channel of the PIP unit.
Block diagram
By default, the PIP appears in the bottom righthand corner of the screen when
it is turned on. It can be moved to any of the other corners of the screen at the
press of a button. Note that the PIP quality is not as good as the main picture.
That doesn’t matter – it’s the tuner section of the older unit that we’re really
after and provided that still works, it
can be pressed into service.
If you don’t have a second VCR,
you can probably obtain a junked
unit quite cheaply from a video repair
shop. Don’t worry too much about the
tape transport mechanism – just make
sure that the tuner/RF section works.
An old Beta player could probably be
picked up for a few dollars (or even
12 Silicon Chip
given away), for example.
Although using two VCRs to provide the two channels is the obvious
way to go, it may be possible to modify
the TV set in some cases so that it can
function as a signal source. That way,
only one VCR would be necessary to
provide the second channel. Modifying the TV set would involve breaking
the audio and video signal paths at the
appropriate points so that the PIP unit
can be interposed.
Fig.2 shows the block diagram of
the TV PIP Unit which can be divided
into audio and video sections. The
audio section (IC5, IC6a, IC6b & IC6d)
accepts the stereo inputs from the
VCRs and produces a single output
(AUDIO OUT) which may be switched
bet
ween either VCR or muted. In
addition, the left and right channels
of the selected source are mixed to
produce a mono signal which is fed
to the video modulator audio input.
The video outputs from the VCRs
are fed to the video inputs of the PIP
board. The output from this board
is either video 1, video 2 or a picture-in-picture signal. This output is
then split two ways. First, it is buffered by driver stage Q4 to provide the
video output signal. And second, it is
fed to the video modulator which produces the alternative RF output signal.
As mentioned before, the remote
transmitter controls all the functions
of the PIP unit. The PIP button switches the picture-in-picture display on
or off, while the SWAP button below
it switches the PIP and full-screen
channels (the audio automati
cally
swaps as well). You can also use the
adjacent audio SWAP button to switch
the sound from the main picture to the
PIP, or vice versa.
The ROTATE button selects which
corner of the screen plays host to the
PIP. This button sequentially moves
the PIP display anticlockwise to the
next corner of the screen each time it
is pressed.
Finally, as its name implies, the
MUTE button kills the audio.
The signals from the remote control
unit are picked up by a remote control
receiver circuit which is based on IC1.
Its output is then fed to the control
logic block (IC2-IC4) and this in turn
controls the audio switching and the
PIP board.
Fig.1: the PIP Unit accepts
video and audio signals
from two VCRs. The
processed output from the
PIP Unit is then fed to the
TV set, either via the
antenna socket or via video
and audio inputs (if fitted).
Circuit details – transmitter
Fig.3 shows the circuit for the IR
Transmitter. IC1 is an SM5021B encoder which outputs a unique code for
each switch. This code gates a 38kHz
carrier on and off and the output at
pin 15 then drives Darlington transistor pair Q1 & Q2. These in turn drive
IRLED1 via a 4.7Ω current limiting
resistor. The 38kHz carrier is derived
by dividing the 455kHz oscillator frequency at pins 12 & 13 by 12.
LK1 and LK2 are included to alter
the coding for each switch. This will
Fig.2: block diagram of the PIP
Unit. The PIP board (bottom,
centre) processes the video
signals from the two VCRs and
produces a single PIP signal. It
also controls the logic
circuitry which switches the
audio signals from the two
VCRs.
April 1997 13
Fig.3 the circuit for
the IR Transmitter.
IC1 is an SM5021B
encoder which
outputs a unique code
for each switch. This
code gates a 38kHz
carrier on and off
and the output at pin
15 drives Darlington
transistor pair Q1
& Q2. These in turn
drive IRLED1.
avoid conflict with another remote
control which uses the same device.
Normally, these can both be left open
for the default coding. Connecting
either or both pins 1 & 2 of IC1 to
ground will change the code.
Circuit details – PIP unit
Refer now to Fig.4 for the circuit
details of the PIP Unit. It’s designed
around the PIP board which, as mentioned above, comes as a pre-built
module.
Starting at the top lefthand corner,
IRD1 picks up the signals from the
handheld transmitter. This 3-terminal
device is actually a bit more complicated than it looks. It contains an IR
receiver diode, an amplifier tuned to
38kHz, a 38kHz bandpass filter, an
automatic gain control (AGC) section
Specifications
Video
Picture-in-picture size .............................Less than 1/6th full screen
Video output ...........................................1Vp-p (adjustable)
Modulator output ....................................Channel 0 or 1 mono audio
Audio (wrt 100mV in or out)
Frequency response ...............................-0.25dB at 10Hz & -1dB at 60kHz
and a detector. Its output is a digital
pulse train identical to that generated
by the transmitter but inverted.
Q1 is used to re-invert the signal,
after which it is fed to pin 2 of decoder
IC1 (SM5032B). The decoding links
LK1 and LK2 must match those in the
transmitter, to ensure compatibility.
IC1 has eight outputs (A-H) and
these match the switches in the transmitter. In this circuit, however, we
only use the A, B, C, E & F outputs
which are all momentary action.
Pressing the ROTATE (A) switch on
the transmitter will produce a high
output on the ‘A’ output of decoder
IC1. Similar
ly, pressing the other
buttons on the transmitter produces
highs on the other decoder outputs.
The ‘C’ output (PIP) of IC1 drives
the clock input of flipflop IC2a. Each
time ‘C’ goes high, IC2a’s Q output
(pin 1) toggles (low to high or high
to low). When this output goes high,
the output of Schmitt NAND gate
IC3d goes low. This selects the picture-in-picture function for the PIP
board.
The ‘A’ output (ROTATE) of IC1 is
buffered by gates IC3a & IC3b. When
the ‘A’ output goes high, the inputs to
IC3c are pulled high via the .012µF
capacitor and IC3c’s output goes low.
After about 120µs, the capacitor charges via its associated 10kΩ resistor and
so IC3c’s output goes high again.
As a result, IC3d delivers a 120µs
high-going pulse to the PIP input
of the PIP board (assuming that pin
8 of IC3d is high). This short pulse
instructs the PIP board to rotate the
picture-in-picture display to the next
position on the screen. The pulse
duration is not critical by the way
and can be anywhere between 1µs to
10ms for the rotate function to work
correctly.
The ‘B’ output of IC1 drives a second flipflop designated here as IC2b.
This also toggles its Q output (pin
13) at each positive going pulse to
Total harmonic distortion ........................< 0.01% from 20Hz to 20kHz
Signal-to-noise ratio ������������������������������78dB wrt 100mV & 20Hz to 20kHz
filter with input unloaded; 88dB wrt
100mV & 20Hz-20kHz filter with
input loaded by 1kΩ resistor
Crosstalk between any two channels .....-56db worst case at 10kHz
Maximum signal handling .......................3V RMS
Signal gain .............................................0dB (x1)
14 Silicon Chip
Fig.4 (right): the signals from the
handpiece are picked up by IRD1
and decoded by IC1. The decoded
outputs then drive the PIP module via
logic circuitry. CMOS analog switch
IC5 switches the audio signals and is
controlled by IC1 via flipflops IC4a
& IC4b and transistors Q1 & Q2. The
modulator produces an RF output
signal on either CH0 or CH1.
Mute level ...............................................-63dB
April 1997 15
Fig.5: install the parts on the PC board as shown in this wiring
diagram. Note that the two links shown dotted are mounted on
the main board beneath the PIP module.
TABLE 1:RESISTOR COLOUR CODES
No.
2
1
14
1
2
3
7
1
2
1
1
16 Silicon Chip
Value
100kΩ
39kΩ
10kΩ
5.6kΩ
4.7kΩ
2.2kΩ
1kΩ
180Ω
100Ω
75Ω
4.7Ω
4-Band Code (1%)
brown black yellow brown
orange white orange brown
brown black orange brown
green blue red brown
yellow violet red brown
red red red brown
brown black red brown
brown grey brown brown
brown black brown brown
violet green black brown
yellow violet gold brown
5-Band Code (1%)
brown black black orange brown
orange white black red brown
brown black black red brown
green blue black brown brown
yellow violet black brown brown
red red black brown brown
brown black black brown brown
brown grey black black brown
brown black black black brown
violet green black gold brown
yellow violet black silver brown
Use the shielded cable and the connectors supplied with the PIP module to
make the connections to the main board. A small round piece of red Perspex is
fitted to the front panel to provide a window for the infrared receiver (IRD1).
the clock input. In this case, the Q
output drives the SWAP input of the
PIP board. This instructs the PIP board
to swap the main picture with the PIP.
When power is first applied to IC2a
and IC2b, their reset inputs (pins 4 &
10) are pulled high via a 10µF capacitor. This resets their Q outputs low.
The 10µF capacitor then charges via
its associated 100kΩ resistor, so that
the resets are released after about one
second. The low Q outputs ensure
that the power on default settings for
the PIP board are: (1) PIP off; and (2)
Video Input 1 selected.
The ‘B’ output of IC1 also drives the
clock input of flipflop IC4a, via diode
D1. This swaps the audio channel
whenever the video swap function
is enabled. Similarly, the ‘E’ output
of IC1 also drives IC4a’s clock input,
this time via diode D2, to perform the
audio swap function. Let’s see how
this all works.
As shown, the output of IC4a drives
transistor Q2 via a 10kΩ resistor. This
transistor effectively inverts and level
shifts the 5V signal from IC4a to a
12V signal which is then applied to
pin 10 of IC5.
IC4b and Q3 function in exactly the
same fashion. In this case, however,
the clock (CK) input of IC4b is driven
by the ‘F’ output of decoder IC1. The
level shifted output appears at Q3’s
collector and is fed to pin 9 of IC5.
Audio switching
IC5 is a 4052 CMOS analog switch.
It is basically a 2-pole 4-way switch
which is controlled by the signals on
its A & B inputs (pins 9 & 10).
When A & B are both low, the X0
and Y0 inputs are selected and fed
The switches on the PIP module must
be set exactly as shown here; ie, two
switches down, the rest up.
through to the X and Y outputs (pins
13 & 3). Similarly, if A is high and
B is low, the X1 and Y1 inputs are
selected. And if B is high, either
X2 or X3 and either Y2 or Y3 are
selected, while X0, X1, Y0 and Y1
are all open.
Note, however, that inputs X2, X3,
Y2 & Y3 are all connected together
and biased to half supply (V/2). They
are also AC-coupled to ground via a
10µF capacitor. If B is high, X2 & X3
are connected to the X output, while
Y2 & Y3 are connected to the Y output.
The left and right audio signals from
VCR 1 are fed to the X0 & Y0 inputs
of IC5, while those from VCR 2 are
fed to the X1 & Y1 inputs. Each input
is AC-coupled via a 10µF capacitor
and biased to half supply via a 10kΩ
resistor. In addition, a 1kΩ resistor is
included in series with each input to
provide current limiting.
If A & B are both low, it follows
that the signals from VCR 1 are fed
through to the X & Y outputs of IC5.
Similarly, if A is pulled high (ie, Q2
switches off), the signals from VCR 2
are fed through instead. And finally,
if B is pulled high, no input signals
are selected and the X and Y outputs
are shunted to ground via the 10µF
capacitor connected to X2, X3, Y2 &
Y3; ie, the audio is muted.
When power is first applied, flip
April 1997 17
The various inputs and outputs are all run via RCA sockets at the rear of the
unit. Note that the power supply socket must be insulated from the rear panel
if a metal label is used.
flops IC4a & IC4b are set via the 10µF
capacitor connected between their
Set inputs (pins 8 & 6) and the +12V
supply rail. This sets the Q outputs
high and the collectors of Q2 and
Q3 low. Thus at power up, the audio
signals from VCR 1 are selected and
the muting is off.
The left & right audio signals
from IC5 are buffered using op amps
IC6a and IC6b. The outputs from
these stages appear at pins 7 & 14
respectively and are fed to the output
sockets via 100Ω resistors and 10µF
capacitors.
In addition, the left and right channels are mixed via 10kΩ resistors and
fed to amplifier stage IC6d. Its pin
14 output in turn drives the audio
input of the modulator via a 10µF
capacitor. VR1 provides a level setting
adjustment.
PIP board
While we do not propose to describe
in detail how the PIP board works, we
can give a precis of its operation. A
video signal consists of luminance
(brightness) and chrominance (colour)
information, mixed with colour burst
and line and frame sync pulses.
The line sync pulses indicate the
beginning and end of each line in
the picture; ie, from the far left to the
far right of the TV screen. The video
luminance and colour signals are
present between these sync pulses
and produce the picture information
in each line. The frame sync pulses
indicate the beginning and end of a
Where To Buy The Parts
The major parts for this design are available as follows:
(1) PIP module plus main PC board: Av-Comm Pty Ltd, PO Box 225,
Balgowlah, NSW 2093. Phone (02) 9949 7417; Fax (02) 9949 7095. Price
– $209 plus $10 p&p. Please quote Cat. K1400 (available end of May 1997).
(2) Complete IR transmitter kit plus all IR receiver parts (please specify
no PC board for receiver when ordering): Oatley Electronics, PO Box 89,
Oatley, NSW 2223. Phone (02) 9584 3563; Fax (02) 9584 3561. Price $30
plus $3.50 p&p.
(3) Astec UM1285AUS 0/1 video modulator: Dick Smith Electronics (Cat.
K-6043).
18 Silicon Chip
complete picture.
In order to shrink the full-sized
picture into a PIP size, the line sync
information must be altered so that
the picture is positioned on a different
part of the screen. This is done in two
ways. First, the line length for the PIP
is reduced by discarding some of the
video information so that it fits into a
smaller space. And second, the num
ber of lines is reduced to decrease the
picture height.
The way in which this is done is
rather complicated. First, the required
information for each video frame is
sampled using a fast A-D converter
and stored in a dual-port RAM. The
term “dual-port” simply means that
we can simultaneously store information in memory and retrieve it, without halting either process. The stored
video information is then retrieved
from the memory at the appropriate
rate, reconverted to analog format and
inserted into the main (full-screen)
video signal.
Basically, all we are doing is substituting PIP video information over
part of each line for the main picture,
until the PIP is complete. Because of
this, the information retrieved from
the RAM does not contain vertical or
horizontal sync pulses, since these
would upset the operation of the
main picture.
The video output from the PIP
board goes to two separate circuits:
(1) a buffer stage based on transistor
Q4; and (2) to the modulator.
VR2 sets the video level into the
base of Q4. This transistor is wired as
an emitter follower and the resulting
signal is coupled to the video output
socket via a 470µF capacitor. The
75Ω emitter resistor sets the output
impedance.
VR3 sets the input level for the
video modulator. This modulator provides an RF output on either channel 0
or 1, depending on the channel select
linking option. Power to the modulator is derived from the +12V rail via a
180Ω current limiting resistor.
Power supply
Power for the circuit is derived from
a 12VAC plugpack. It’s output is fed
to bridge rectifier D3-D6 and filtered
with a 2200µF capacitor to derive a
16VDC (nom.) supply. This is then
applied to 3-terminal regulator REG1
which provides a 12V supply rail for
the PIP board and ICs 5 & 6.
A 3-terminal regulator on the PIP
board provides a separate +5V rail
and this is used to power IRD1 and
ICs 1-4. It also drives a LED power
indicator via a 560Ω resistor.
Finally, a half-supply voltage is derived from a voltage divider consisting
of two 10kΩ resistors. This is buffered
by unity gain amplifier stage IC6c and
the resulting V/2 output used to bias
the audio input signals to IC5.
Construction
The parts for the PIP Unit are mounted on a PC board coded 02302971 and
measuring 197 x 154mm. This board
accommodates the preassembled PIP
module, the modulator and all the
support circuitry. You can buy the
PIP module and the PC board from
Av-Comm Pty Ltd, while the handheld transmitter and receiver parts
are available from Oatley Electronics.
Dick Smith Electronics stocks the
specified video modulator.
Fig.5 shows the parts layout on the
PC board. Before mount
ing any of
the parts, check the board carefully
for shorts between the tracks and for
breaks in the copper pattern. You
should also check that the mounting
holes for the PIP board and for REG1
are drilled to 3mm and that the mounting holes for the modulator earth lugs
are correct.
Begin the assembly by installing
the links and the resistors. Note that
two of the links are shown dotted, to
indicate that they go under the PIP
module – don’t forget these. Table 1
PARTS LIST
1 PC board, code 02302971, 197
x 154mm
2 self-adhesive labels for front &
rear panels, 215 x 34mm
1 remote control transmitter label,
31 x 63mm
1 plastic case, 225 x 165 x 40mm
(Jaycar Cat. HB5972)
1 PIP board (from Av-Comm)
1 video modulator, Astec
UM1285AUS 0/1 (DSE Cat.
K-6043)
1 12VAC 500mA plugpack
2 2 x 2-way PC-mount RCA
sockets (Altronics P-0211)
1 RCA panel-mount socket
1 DC panel socket to suit
plugpack
1 SPDT toggle switch (S1)
1 TO220 heatsink, 19 x 19 x
6mm
1 50kΩ horizontal trimpot (VR1)
2 1kΩ horizontal trimpots
(VR2,VR3)
1 400mm length of 0.8mm tinned
copper wire
1 500mm length of hook-up wire
4 self-tapping screws to secure
board to case
4 3mm dia. x 9mm screws & nuts
4 5mm spacers
1 3mm dia. x 6mm screw and nut
1 8mm ID grommet (to insulate
DC socket)
15 PC stakes
1 10mm dia. x 3mm red Perspex
for IR sensor window
Semiconductors
2 4013 dual-D flipflops (IC2,IC4)
1 4093 quad Schmitt NAND gate
(IC3)
1 4052 dual 1-to-4 analog
multiplexer/demultiplexer
(IC5)
1 TL074, LF354 quad op amp
(IC6)
1 7812 12V 3-terminal regulator
(REG1)
3 BC548 NPN transistors (Q2,
Q3, Q4)
2 IN914, 1N4148 signal diodes
(D1,D2)
4 1N4004 1A diodes (D3-D6)
1 3mm LED (LED1)
Capacitors
1 2200µF 16VW PC electrolytic
1 470µF 16VW PC electrolytic
1 47µF 16VW PC electrolytic
1 22µF 16VW PC electrolytic
14 10µF 16VW PC electrolytic
1 .012µF (12n or 123) MKT
polyester
Resistors (0.25W 1%)
2 100kΩ
5 1kΩ
13 10kΩ
1 180Ω
1 5.6kΩ
2 100Ω
1 4.7kΩ
1 75Ω
3 2.2kΩ
8-Channel IR Transmitter
1 Magnavox remote control
handpiece (includes IRLED
and battery clips)
1 455kHz resonator (X1)
1 PC board
2 AAA cells
2 PC stakes
Semiconductors
1 SM5021B encoder (IC1)
1 BC548 NPN transistor (Q1)
1 C8050 NPN transistor (Q2)
Capacitors
1 10µF 16VW PC electrolytic
2 100pF (100p or 101) ceramic
Resistors
2 1kΩ
1 4.7Ω
8-Channel IR Receiver
1 SM5023B remote control
receiver (IC1)
1 BC338 NPN transistor (Q1)
1 PIC12043 infrared receiver
(IRD1)
Capacitors
1 10µF 16VW PC electrolytic
1 .001µF (1n0, 102 or 1000p)
ceramic
Resistors
1 39kΩ
1 10kΩ
1 4.7kΩ
April 1997 19
RF OUT
+
+
MUTE
+
AUDIO
+
ROTATE
+
VIDEO
PICTUREIN-PICTURE
REMOTE
CONTROL
SWAP
SWAP
+
PIP
Fig.7: the full-size artwork for the rear panel. It can be photocopied and affixed to the rear panel using double-sided adhesive tape.
AUDIO OUT
IN2
IN1
12VAC
IN
+
R
+
VIDEO
IN 2
+
R
+
+
L
+
VIDEO
IN 1
+
VIDEO
OUT
Fig.6: this full-size artwork can be used as a drilling template for the front panel.
POWER
+
+
+
+
L
+
+
TV PICTURE-IN-PICTURE
Fig.8: this is the full-size front panel
artwork for the hand-held transmitter.
lists the resistor colour codes but it is also a good
idea to check each value using a digital multimeter,
just to make sure.
The diodes can be mounted next, taking care to
ensure that they are oriented correctly. Note that
two types are used on the main PC board: (1) the
1A 1N4004s which have a black body; and (2) the
smaller 1N914s which are usually orange in colour.
The 14 PC stakes can now be installed on the PC
board, followed by the ICs. Take care with the orientation of each IC and check that the correct type has
been installed at each location before soldering. Note
particularly that IC1 & IC6 are oriented differently
to the other ICs.
The LK1 and LK2 linking options for IC1 can be
left open circuit, unless you already have an identical
IR remote control with the same coding.
The four transistors are all BC548 types and these
must be oriented exactly as shown. REG1 is mounted
horizontally, with its leads bent at rightangles so that
they pass through the PC board. It is fitted with a
small heatsink and bolted to the PC board using a
3mm screw and nut.
The capacitors can now be installed, along with
IRD1, LED1 and the trimpots. Be sure to orient IRD1
with its bubble-shaped lens towards the front. LED1
should be mounted at full lead length, so that it can
later be bent over and pushed through its mounting
hole in the front panel hole.
The two RCA socket sets must have their plastic
locating pins removed before they are mounted.
Remove these using sidecutters, then solder the RCA
sockets in position, taking care to ensure that their
bottom surfaces sit flush with the board.
The video modulator is mounted in the top
righthand corner of the board. As shown, the unit is
wired for channel 0. If you want channel 1, simply
transfer the lead from the CH0 position to the CH1
position.
The PC board assembly can now be completed by
mounting the PIP module. This board is mounted
on 5mm spacers and secured using 3mm screws and
nuts. Wire up the board using the supplied shielded
leads and the red/black power lead. Don’t forget to
solder a length of hookup wire from the onboard 5V
regulator output to the +5V PC stake on the main
PC board.
Final assembly
The completed assembly is housed in a standard
plastic instrument case measuring 225 x 165 x 40mm.
20 Silicon Chip
The infrared transmitter should only take a few minutes to assemble. Notice
how the two transistors are bent over, so that they sit flat against the board. The
board simply clips into position in the case.
Begin the case assembly by affixing
the labels to the front and rear panels.
This done, drill out the holes on the
rear panel for the RCA sockets, the
power socket and the RF OUT socket.
The best way to go about this is to first
drill small pilot holes and then carefully enlarge each hole to the correct
size using a tapered reamer.
Moving now to the front panel, drill
the holes for the power switch and its
adjacent indicator LED. You will also
have to drill a 10mm hole in the front
panel in line with IRD1. We fitted a
10mm-dia. red Perspex window to this
hole, rather than simply leave it open.
The various items can now all be
mounted in position and the wiring
completed as shown in Fig.5. Note
that the PC board assembly is secured
using self-tapping screws which go
into integral pillars in the base of the
case. Two small self-tapping screws
are also used to secure the stereo RCA
sockets to the rear panel.
Important: if a metal label is used
on the rear panel (eg, Dynamark),
be sure to insulate the power socket
from the panel. This can be done by
stripping back the label from around
the mounting hole and then fitting
a large insulating washer under the
mounting nut. If this is not done, the
metal label will short one side of the
12VAC power supply to ground.
Transmitter assembly
Very little work is required to assemble the IR transmitter, as Fig.9
shows. It’s mainly a matter of soldering a few parts to the transmitter
board. Take care to ensure that the
infrared LED is installed with the
correct polarity and note that Q1 is a
BC548 while Q2 is a C8050.
After that, all you have to do is attach the label to the transmitter case
and cut out the holes for the switch
pads, as marked. You will also have
to cut off the switch pads on the rubber membrane that were originally
intended for the volume and CD
selections.
The two halves of the case are simply clipped together after installing
the two 1.5V AAA cells.
Testing
Now for the smoke test but first go
back over your work carefully and
check for possible wiring errors. In
particular, check that all components
are correctly oriented and that the
correct part has been used at each
location.
This done, apply power and check
that there is +12V at the output of
REG1 and +5V at the output of the
regulator on the PIP board. If these
voltages are OK, switch off and set two
of the DIP switches on the PIP module
to the down position, as shown on
Fig.5. These select the video sources
for the main and PIP display.
It’s now simply a matter of connecting the unit as shown in Fig.1
and testing it for correct operation.
Remember to tune the TV set to the
appropriate channel (either CH0 or
CH1), if you are using the RF output
from the PIP Unit. Of course, this step
will not be necessary if you are feeding
the audio/video outputs from the PIP
Unit to the TV set.
Now apply power and check that
the signal applied to INPUT 1 appears
on the screen as the main picture. At
this stage, there should be no PIP. If
this is correct, adjust VR3 to obtain the
correct contrast range and to prevent
Fig.9: take care with the orientation
of the infrared LED and don’t confuse
transistors Q1 & Q2 when installing
the parts on the transmitter board.
The two transistors are installed flat
against the board as shown in the
photo at the top of the page.
overmodulation (assum
ing the RF
output is being used). If the direct
video output is being used, adjust
VR2 for correct contrast instead. VR1
is adjusted for a normal sound level.
You can now check the remote
control. Select PIP and check that a
small picture corresponding to the
second video input appears in the
lower righthand corner of the screen.
If it does, check that the ROTATE and
video SWAP functions work – the
sound should follow the main picture.
Finally, check that the audio SWAP
SC
and MUTING functions work.
April 1997 21
|