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IR remote control
for old TV
I have recently put together an
infrared remote and attached it to
my old TV (with pushbutton channel selection) as an on/off switch
and channel changer. It is operating
fine as it is but I am looking for a
method of perhaps storing the last
sent signal in some kind of a buffer
to be retransmitted when the next
button is pressed, thus turning of
the previously selected channel.
As it is, you have to turn off the
channel you are on before selecting
the new channel.
I have used two Dick Smith Electronics 4-channel infrared remote
control kits (Cat. K-2810). I have
used Channel 8 to operate the on/off
relay, with the other seven outputs
for the seven channel positions.
Each of these outputs drives two 5V
relays to switch the signals. These I
have connected directly to the back
of the original switch.
These kits use the MC145026
9-bit trinary encoder IC for the
transmitter and the MC145027 9-bit
trinary decoder IC for the receiver.
about two years ago and find that it
works just fine. Now I’m about to install another one in a 1992 Renault 19.
My concern is that a radiator expert
on a motoring radio program raised
the possibility (and he quoted actual
occurrences) of electrolysis occurring
with cars fitted with aluminium radiator cores. Apparently, a current of
50mA is enough to ruin a radiator in
a short time.
My knowledge of electronics is limited to soldering kits together. There-
The signal is inverted and two
74HC74 dual D flipflops are used
as latches or not, depending on the
intended application. Could the VT
outputs be utilised in some way for
this purpose?
Could you please suggest possible components and/or a circuit
which may suit this application?
(W. W., Murwillumbah, NSW).
• We don’t understand why you
have to turn off the presently selected channel when a new channel
is selected. In any conven
tional
remote system, such as a hifi amplifier, it is not necessary to turn
off individual program sources (eg,
CD player) when another program
source is selected. Of course, in
an integrated system, sources are
usually turned off when a new one
is selected but it does not have to
be done that way.
Nor can we see any way of storing
the last transmitted signal. Possibly
a better way would be to have a logic
selector system, perhaps using a
counter (4017?) or shift register so
that when a new count (data) was
selected, the old one could naturally
be de-selected.
fore, I would appreciate it if you could
clarify as to whether there is a possibility of electrolysis occurring with the
coolant level alarm. I understand that
all the late model cars are fitted with
aluminium radiator cores. It would be
great if you could show how to check
if electrolysis is happening, with a
multimeter. Do aluminium radiator
equipped cars have a sacrificial anode
in the system? (J. B., Surrey Hills, Vic).
• While there is a potential problem
with electrolysis occurring in alumin-
ium radiators, the sensor current used
in our circuit is very small, at around
47 microamps. This is determined
by the 100kΩ sense resistor and 4.7V
supply.
You can confirm this current by
connecting your multimeter in series
with the sensor lead.
As far as we know, there is no sacrificial anode in car radiators. Inevitably
though, the car’s aluminium head will
perform the same function.
Inverter for
a scanner
I have a 12VDC car battery and I
wish to get 10VAC <at> 50Hz from it to
power a VHF and UHF scanner drawing about 350mA. Have you published
a circuit for such an inverter? (A. P.,
Gladstone, Qld).
• The project most suitable to your
application would be our 12V-to240VAC 40W inverter described in
the February 1992 issue. You would
have to use it with a 10VAC plugpack
to drive your scanner.
However, we wonder if the scanner does not already have a 12V DC
input or failing that, does not actually
run from 12V DC after the 10VAC is
rectified. You may even be able to
feed 12V DC into the 10VAC input,
if it is followed by a bridge rectifier.
It would be worthwhile investigating
this point.
Notes & Errata
LED FUN, March 1999: we have been
advised by Dick Smith Electronics that
a batch of PIC12C508 microcontrollers
have been found to latch into Mode 1
when Mode 3 is selected. The solution
is to change all 2.2kΩ resistors in the
circuit to 270Ω. All resistors in the
supplied kits will now be 270Ω. SC
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