This is only a preview of the July 1996 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 VGA Digital Oscilloscope; Pt.1":
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This simple device lets
you operate your VCR
using its remote control
from another room in
the house. It picks up
the signal from the
handpiece and sends
it via a 2-wire cable
to an IR LED located
close to the VCR.
Remote control
extender for VCRs
By RICK WALTERS
have two or more TV sets which
M
are linked (via antenna cable) to a single VCR. The problem is,
you can’t directly control the VCR from another room in the house.
ANY HOUSEHOLDS NOW
For example, you might want to watch a video on a second set in
the bedroom but if you want to stop, fast forward or freeze-frame
the action, you have to “walk” the remote control to the room where
the VCR lives.
Wouldn’t it be great if you could control the VCR directly from
your bedroom?
Well, the answer is you can – by building this simple Remote
Control Extender circuit. It packs into a small plastic zippy case
and should only take you half an hour to assemble.
In use, the device sits on top of the remote TV set (or in some
other convenient location in the room) and picks up the signals
from the VCR’s remote control. It then converts these signals into
electrical impulses and feeds them down a thin 2-wire cable to an
IR (infrared) LED placed in front of the VCR.
Because the IR pulses from this LED mimic the IR pulses from
the remote control handpiece, the VCR responds in exactly the
same fashion. It’s as though the handpiece was being operated in
the same room as the VCR. Fig.1 shows the basic scheme.
It’s been done before
OK, we confess that the idea is not new – designs for remote
control extenders have been published before. Our last unit was
described in April 1994 and was very popular. However, the SL486
IR preamplifier IC used in that design is no longer available and so
this circuit is now obsolete.
July 1996 31
Fortunately, a new IC which can do
the job has recently appeared. This
device, from Dick Smith Electronics,
carries a Z1954 type designation and
is actually a complete IR receiver subsystem. An equivalent part, designated
PIC12043, is available from Oatley
Electronics.
In both cases, the device comes in a
TO-220 style package with an integrated plastic lens on one side. This lens
sits in front of an integral IR receiver
diode. As well, the device includes
amplifier, limiter and bandpass filter
stages, plus a demodulator. Its on-axis
reception distance is quoted as eight
metres but this will obviously depend
on the intensity of the light output
from the remote control.
Circuit details
Because so much circuitry is packed
into the Z1954, the final circuit of the
extender is much simpler than previous designs – see Fig.2. Apart from the
Z1954, there’s just one low-cost CMOS
IC, a transistor, an IR LED and a few
sundry bits and pieces.
Each time the VCR’s remote control is operated, it sends out bursts of
pulsed IR radiation. These bursts are
picked up by the IR photodiode inside
IC1, converted to electrical signals
and fed to the internal amplifier and
filter stages. The demodulated output
appears at pin 1 and is fed to pin 2 of
NOR gate IC2a (note: this gate is actually wired in parallel with IC2d but
Fig.1: the unit picks up infrared (IR) light from the VCR’s remote control and
converts it to an electrical signal. This signal is then sent down a 2-wire cable
and drives an IR LED located in the same room as the VCR.
wave oscillator stage based on NOR
gates IC2b and IC2c. The output from
this stage appears at pin 10 of IC2c
and is fed to pin 3 of IC2a, where it is
gated by the signal from IC1.
The output from IC2a is depicted
by the bottom waveform in Fig.3.
This signal drives transistor Q1 via
a 2.2kΩ resistor. Q1 in turn drives
IRLED1 which is at the end of the
2-wire cable and is positioned where
it can be “seen” by the sensor in the
VCR. Because the signal drive
to IRLED1 mimics the transmitted signal, the VCR will
obey all the remote control
functions.
Trimpot VR1 allows the
oscillator frequency to be
adjusted to suit your VCR (or
whatever piece of equipment
you are controlling). The frequency is usually not all that
critical and will typically be
somewhere around 30-40kHz.
Power for the circuit is derived from a 9V DC plugpack
supply via reverse-polarity
protection diode D1. The resulting supply rail is filtered
using a 470µF capacitor and
regulated to 5.1V using ZD1
and a 470Ω resistor.
Finally, an acknowledge
Fig.2: the circuit is based on IC1 which is a complete IR receiver subsystem. When IR
LED
is connected in series
light is received, IC1’s output switches high and low. This signal is applied to NOR
with a 1kΩ resistor between
gate IC2a,d and gates an oscillator signal generated by IC2b and IC2c. The gated
the positive supply rail and
signal then drives transistor Q1 which in turn drives infrared LED IRLED1.
32 Silicon Chip
we’ll just talk about IC2a to simplify
the circuit description).
The top two waveforms in Fig.3
depict the transmitted signal and the
signal at pin 1 of IC1. Note that the
latter waveform has been stripped
of the carrier and that it is inverted
compared to the transmitted signal.
Unfortunately, we don’t want to lose
the carrier but we don’t have a choice
with IC1. To overcome this, a suitable
carrier is regenerated using a square-
lead will be the longer of the two. The
IR sensor (IC1) should be installed so
that it sits about 5mm above the board
surface.
The IR LED (IRLED1) is connected
via a suitable length of figure-8 cable.
This is wired as follows:
(1) slide a 50mm length of 5mm-diameter heatshrink tubing over one end
of the cable;
(2) separate the leads at this end
and slide a 30mm length of 2mm-diameter heatshrink tubing over each
lead;
(3) strip the ends of the leads and
solder them to the LED. Connect the
black trace lead to the cathode and the
plain lead to the anode.
(4) Push the 2mm heatshink tubing
over each soldered joint and shrink it
down using a hot-air gun. This done,
cover both leads with the 5mm tubing
and shrink it down as well.
The other end of the cable goes to
the jack plug. Connect the black trace
lead to the centre pin – ie, to the tip
terminal. The plain lead goes to the
outer pin.
Fig.3: this diagram show the waveforms at various points
in the circuit. The output waveform is obtained by gating
the middle two waveforms together using parallel NOR
gates IC2a and IC2d.
Testing
Fig.4: install the parts on the PC board as shown in this diagram,
taking care to ensure that all polarised parts are correctly oriented.
the output of IC1. Normally, IC1’s
output is high and LED 1 is off. When
the remote control is operated, IC1’s
output pulses low and LED 1 lights
to indicate that the code is being
received.
Putting it together
The circuit is built on a small PC
board coded 15107961. This should
be carefully checked for etching faults
before you begin assembly.
Fig.4 shows where the parts go. Fit
the two wire links first, then the six
resistors and the two diodes. This
done, install the trimpot, transistor
Q1, both jack sockets and the ca
pacitors. Make sure that the diodes
and the electrolytic capaci
tors are
correctly oriented.
Next, install the acknowledge LED
so that it sits about 12mm proud of
the PC board. Again, make sure that
the LED polarity is correct – the anode
The unit can now be bench tested
to check that it is working properly.
Before applying power, check that the
centre pin on the 2.5mm power plug is
positive. If it is, plug it into the power
socket and plug the IRLED lead into
the other socket.
Now aim the remote control at the
IR sensor, press a button and check
that the acknowledge LED flashes. If
it doesn’t, check the supply voltage to
IC1 and IC2 (it should be 5.1V).
If everything is OK so far, place the
IR LED in front of the VCR and position
the Remote Control Extender in another room. Operate the remote control
and check to see if the VCR responds.
If it doesn’t, hold down a button on
the remote control and slowly adjust
VR1 until it does.
SILICON
CHIP
Fig.5: check your board carefully against this full-size etching
pattern before mounting any of the parts. Fig.6 (right) shows the
full-size front panel artwork.
REMOTE CONTROL
EXTENDER
July 1996 33
PARTS LIST
1 PC board, code 15107961, 78
x 33mm
1 plastic utility case, 28 x 54 x
83mm
1 9V DC plugpack with 2.5mm
plug
1 3.5mm PC-mounting socket
1 2.5mm PC-mounting socket
1 3.5mm line plug 2.5mm
1 50mm length 5mm-dia. heatshrink tubing
1 60mm length 2mm-dia heatshrink tubing
1 length of figure-8 light duty
speaker cable to suit
1 10kΩ horizontal mount trimpot
(VR1)
The assembled PC board fits neatly inside a standard plastic case and is held in
place by the collars of the jack sockets and by the acknowledge LED.
Once the VCR operates, find the
minimum and maximum trimpot
settings and adjust it to the mean
position.
If it doesn’t work, go over the PC
board carefully and check for missing or bad solder joints. You should
also check that all polarised parts
(ICs, transistor, LED, diodes and
elec
trolytic capacitors) have been
correctly oriented and that all resistor
values are correct.
Once testing has been completed,
the PC board can be installed in the
case. Note that you will have to drill
four holes (two at each end) to accept
the jack sockets, the acknowledge LED
and the lens of IC1. The PC board is
then pushed down into the case so
that the collars of the sockets protrude
through their respective holes.
After that, it’s simply a matter of
pushing the acknowledge LED into
its hole and aligning the lens of IC1
with its hole, so that it can “see” the
IR pulses from the remote control.
Finally, if you find a plugpack sup-
Semiconductors
1 IR subsystem (IC1); DSE
Z1954 or Oatley Electronics
PIC12043
1 74HC02 quad NOR gate (IC2)
1 BC548 NPN transistor (Q1)
1 1N4004 power diode (D1)
1 5.1V 400mW or 1W zener
diode (ZD1)
1 IR LED, 940nm, Oatley 600D
or equivalent (IRLED1)
1 5mm red LED
Capacitors
1 470µF 16VW PC electrolytic
1 100µF 16VW PC electrolytic
1 680pF 100VW MKT polyester
Resistors (0.25W, 1%)
1 100kΩ
1 1kΩ
1 8.2kΩ
1 470Ω
1 2.2kΩ
1 220Ω
Top: the lens of the IR sensor (IC1)
must be aligned with a hole in the end
of the case, so that it can “see” the
pulses from the remote control. Above
is a close-up view of the IR LED.
ply inconvenient, the unit can be run
from a 9V battery. Its current consumption is around 8mA under quiescent
conditions and around 25mA when
pulsing. Don’t forget to turn it off when
you are finished as the battery will
not last very long if the unit is left on
SC
continuously.
RESISTOR COLOUR CODES
❏
❏
❏
❏
❏
❏
❏
No.
1
1
1
1
1
1
34 Silicon Chip
Value
100kΩ
8.2kΩ
2.2kΩ
1kΩ
470Ω
220Ω
4-Band Code (1%)
brown black yellow brown
grey red red brown
red red red brown
brown black red brown
yellow violet brown brown
red red brown brown
5-Band Code (1%)
brown black black orange brown
grey red black brown brown
red red black brown brown
brown black black brown brown
yellow violet black black brown
red red black black brown
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