'PIC controlled remote TV Tuner'
My parents have an old TV in their bedroom without a remote control. I
would like to add the functionality of a VCR, but without the tape deck
part. I would like to use a PIC to control a sort of TV tuner and
remote power switch. There must be a lot of old TV's that could use a
device like this.
I have absolutely no idea about TV transmission. I understand that it's
transmitted on a carrier frequency, but I will have to look up the
frequencies for my area (we use PAL standard, and I need to get VHF and
UHF channels). Is there a world standard for the frequencies they
Assuming our antenna catches the signal and it comes magically down the
coax, here is what I have to do :
1) Filter the antenna signal for the carrier frequency of a particular
2) To get a 'composite' signal, which is the raw TV signal, I have to
filter out the carrier frequency.
3) Re-modulate this composite signal to a frequency the TV is always
tuned in to.
Am I on the right track? It might be easier to make a VCR out of
coconut shells like on Gilligan's Island. I'll bet there is a chip to
do this because this is how all VCR's work isn't it? Can I buy a
pre-built module etc?
Then comes the remote control bit. I can get an old remote control from
a broken VCR somewhere - which will have a nice case and buttons. Then
I have to decode the signal. Some people have posted Sony protocols etc
but I can't be sure what protocol it will use. Does anyone know how to
capture a code from ANY control (assuming 40kHz IR type) in response to
a button being pressed?
Once I have the tuner figured out, and can decode a remote, they can all
be tied together with the PIC. For the power switch is it better to use
a relay or a triac to switch on the TV?
Thank you, any help appreciated,
> My parents have an old TV in their bedroom without a remote
> control. I would like to add the functionality of a VCR,
> but without the tape deck part.
It sounds like you're making a one-off assembly. Rather
than build a wide bandwidth VHF/UHF tuner and RF modulator,
why not buy a used VCR with remote control?
If you want to include a PIC, have it monitor the VCR remote
control's IR signal for some unique code. When it sees it,
toggle a relay on and off to control power to the TV set.
> Does anyone know how to capture a code from ANY [remote] control
> (assuming 40kHz IR type) in response to a button being pressed?
Set up a breadboard with an IR receiver module. Watch the
module's output pin with an osciloscope, logic analyser,
parallel port pin of a PC (with software pin monitoring),
etc. General protocol might be tricky to reverse engineer
but learning enough to recognize specific button presses
isn't too hard.
David Lions wrote:
> I would like to add the functionality of a VCR, but without the tape
> deck part.
Second hand VCRs with crook transport are a "dime a dozen". Cadge
from the video shop repair department. Garage Sales.
> There must be a lot of old TV's that could use a device like this.
Matched by lots of dead VCRs.
> I have absolutely no idea about TV transmission.
That's a *very good reason* to do the above ;-) All the following
will be on the understanding you want to learn about TV, not because
it is practical to make your own VCR. Except from a kit, like the E-A
Teletext Decoder etc., but that's only if you want to spend money.
Cheaper to buy new VCR! (Less than $400 at Big W)
> I understand that it's transmitted on a carrier frequency, but I will
> have to look up the frequencies for my area
Try the Dick Smith cattledog.
> (we use PAL standard, and I need to get VHF and UHF channels). Is
> there a world standard for the frequencies they transmit on?
Might be, but we wouldn't use it here! :<*)
> Am I on the right track? It might be easier to make a VCR out of
> coconut shells like on Gilligan's Island.
Now you're getting the idea!
> Can I buy a pre-built module etc?
It's called a VCR! See above (i.e., second hand machine; E-A project)
> Then comes the remote control bit. I can get an old remote control
> from a broken VCR somewhere - which will have a nice case and buttons.
Vorlac had some a while back.
> For the power switch is it better to use a relay or a triac to switch
> on the TV?
Much to be said for a relay.
|On Sun, 10 Jan 1999 16:04:32 +1100 David Lions <MAGNA.COM.AU> bjlions
>My parents have an old TV in their bedroom without a remote control.
>would like to add the functionality of a VCR, but without the tape
It is easy to find a junker VCR which still tunes OK but has no hope of
ever playing a tape again. This would serve the remote-control tuning
part of the project. (You also get a clock for free, if you can figure
out how to set it...) For the power on/off, most VCRs have a 12V DC
supply bus which switches on and off with the "Power" button. Connect
the coil of a relay to this bus and the contacts in series with the AC
line to the TV. Usually you'll find the switched supply near the motor
Obligatory safety note: Unlike a TV, it's fairly safe to probe around
inside a VCR since most everything works on low voltages that are
isolated from the power line. But stay away from areas near where the
power cord connects, since there may be line voltage there. It's best to
treat everything as being live if you're not sure what you are doing.
How many of us are sure what we're doing?
Since you aren't using the motors any more, the current drawn by the
relay won't overload the VCR's supply. Now the "Power" button on the
remote will switch the VCR *and* the TV on and off.
> I would like to use a PIC to control a sort of TV tuner and
>remote power switch. There must be a lot of old TV's that could use a
>device like this.
Devices like this (called a "converter box" are still made for cable-TV
tuning. There used to be some for over the air TV but they are probably
hard to find now since most everyone uses cable.
>I have absolutely no idea about TV transmission. I understand that
>transmitted on a carrier frequency, but I will have to look up the
>frequencies for my area (we use PAL standard, and I need to get VHF
>UHF channels). Is there a world standard for the frequencies they
TV broadcasts generally occur on frequencies between 50 and 900 MHz, but
the exact frequencies are determined by politics in each country. There
seems to be some agreement but it is by no means universal.
>1) Filter the antenna signal for the carrier frequency of a particular
TV's and VCRs have a module called the "tuner" which does that. The
tuner module is easily identified since the antenna lead goes into it.
Usually the tuner is in its own metal box to shield out interference.
Old-fashoined tuners are controlled by a knob, while new ones use a
voltage. The low-tech way to control the voltage controlled ones is to
set a voltage with little preset knobs or EEPROM settings, one for each
channel. A voltage-controlled tuner can also be used as part of a PLL
tuning system. Sometimes the PLL circuit is inside the tuner case,
sometimes it is outside.
PLL tuning is based on a synthesizer IC which accepts a binary nunber
(usually through a SPI or IIC port) to select the frequency to be tuned.
The set's microcontroller program includes a formula or table to generate
the proper PLL control number for each channel. Also it is usually
necessary to switch on and off various voltages to the tuner to select a
particular "band" of channels to be tuned. Sometimes the PLL IC handles
this, other times output pins from the microcontroller are used. In the
case of a new tuner having a built in PLL, usually only the SPI or IIC
interface and a few supply voltage are needed.
In any case, the output of the tuner is a RF replica of the TV station's
signal, translated in frequency to about 45 MHz. The output from the
tuner is the same regardless of the frequency of the TV station. Thus,
exactly the same circuit in the TV can be used to further process any
channel. If you're familiar with the design of superheterodyne radio, a
TV works exactly the same way. The tuner's output signal is called the
"IF" signal, for Intermediate Frequency.
>2) To get a 'composite' signal, which is the raw TV signal, I have to
>filter out the carrier frequency.
The next stage in the receiver does that. First the IF signal is
amplified some and passed through a precise filter to remove any signals
from TV channels that are close in frequency to the desired one (the
design of the tuner doesn't reject them very well at all). Then the
signal is amplified a lot more. Next a "detector" stage develops a
voltage coresponding to the instantaneous amplitude of the signal. This
voltage is essentially a baseband composite video signal (as would be
observed at the "VIDEO OUT" RCA jack of a camera or VCR), though it also
has sound information in it as well. Further processing filters the
sound out of the detector signal and passes it to a sound demodulator
stage. A vital support circuit controls the gain of the IF amplifiers to
match the strength of the signal from the antenna.
All the circuitry described in the paragraph above is usually based
around one IC. Especially in VCRs, the IF and detector circuits are
often integrated with the tuner and included in the tuner's case.
>3) Re-modulate this composite signal to a frequency the TV is always
>tuned in to.
For a converter box like you want, it isn't strictly necessary to go by
your plan. Cable TV converters often do not demodulate and remodulate.
Instead they convert the selected chaneel's frequency not to 45 MHz, but
to a frequency of an over the air channel that any TV can receive. They
skip steps 2 and 3 of your process by doing step 1 differently. Usually
a double conversion is involved. It should be possible to use a stock
type of tuner and convert the 45 MHz signal back up to a TV channel,
using a high LO in order to invert the frequencies again.
Obtain a "universal" control sold to replace lost or broken remotes. You
have a much better chance of finding a broken VCR (still suitable for
your project) than the remote that goes with it. Then set the control up
to send your favorite documented protocol.
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