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Video and comms question

F

flint

Jan 1, 1970
0
Hi All,

A question for you clever guys and gals -

I am using a conventional radio control unit (as used for model
planes) to activate servo motors in an experimental setup. This works
well but I now want to add video feedback from a camera. Radio control
is really not a preferred option for me in this appllication and to
keep the overall system simple, a cable would actually be better. The
separation diistance is about 200ft. The cable needs to be as small as
possible.

Is it possible to achieve all of the communications including video
down just a single co-ax? By this I guess I mean can either of these
work? -

A) A single co-ax cable carrying the video but could I somehow 'add
in' the modulated RC control i.e. get rid of the aerial at each end
and suppliment the transmitter and reciever with some electronic
interface to make the direct cable connection. Would the modulated RC
signal screw up the video or visa-versa?

B) Could I achive the same effect but not using the RC unit. i.e.
again by adding a modulated control signal to the video conection.

In order to keep the cable simple, cheap and lightweight, I don't
really want to go for a more conventional video plus RS422 twin
screened twisted pairs setup.

Your comments, and any recommendations, humbly recieved.

Thanks

F
 
M

martin griffith

Jan 1, 1970
0
Hi All,

A question for you clever guys and gals -

I am using a conventional radio control unit (as used for model
planes) to activate servo motors in an experimental setup. This works
well but I now want to add video feedback from a camera. Radio control
is really not a preferred option for me in this appllication and to
keep the overall system simple, a cable would actually be better. The
separation diistance is about 200ft. The cable needs to be as small as
possible.

Is it possible to achieve all of the communications including video
down just a single co-ax? By this I guess I mean can either of these
work? -

A) A single co-ax cable carrying the video but could I somehow 'add
in' the modulated RC control i.e. get rid of the aerial at each end
and suppliment the transmitter and reciever with some electronic
interface to make the direct cable connection. Would the modulated RC
signal screw up the video or visa-versa?

B) Could I achive the same effect but not using the RC unit. i.e.
again by adding a modulated control signal to the video conection.

In order to keep the cable simple, cheap and lightweight, I don't
really want to go for a more conventional video plus RS422 twin
screened twisted pairs setup.

Your comments, and any recommendations, humbly recieved.

Thanks

F
You could insert data in the first few video lines of the video
signal. See LM1881 sync stripper data sheet, for the basic circuit.
Use a switched PNP current source to drive the coax with data at a
suitable time. You could put say one or two bytes in a video line,
quite easily, but with a bit more care you could get say 10 bytes per
line.

Because video is normally a 75R source and 75R termination you need to
drive approx 37R to say 0.5V.
If you require two way data you could use the odd/even flag from the
1881 to set what end is transmitting.

Obviously you will need a micro at either end, which are locked to the
video, and a simple line counter to select the correct line, will
simplify the software.

Elantec/intersil make better video sync strippers that the LM1881,
that may offer a more flexible approach


martin
 
F

flint

Jan 1, 1970
0
You could insert data in the first few video lines of the video
signal. See LM1881 sync stripper data sheet, for the basic circuit.
Use a switched PNP current source to drive the coax with data at a
suitable time. You could put say one or two bytes in a video line,
quite easily, but with a bit more care you could get say 10 bytes per
line.

Because video is normally a 75R source and 75R termination you need to
drive approx 37R to say 0.5V.
If you require two way data you could use the odd/even flag from the
1881 to set what end is transmitting.

Obviously you will need a micro at either end, which are locked to the
video, and a simple line counter to select the correct line, will
simplify the software.

Elantec/intersil make better video sync strippers that the LM1881,
that may offer a more flexible approach

martin

Thanks Martin.

As you may have gathered, I am not skilled in the art (or mystery) of
electronics (I am a mechanical guy) and will need to gather more info
and assistance on taking this further. One issue is going to be cost
but I guess there are some pretty cheap micros or PICs about that
could be considered.

The other issue is going to be how effective the data speed will be
given that I am trying to control something dynamic (it's not a
vehicle or airplane but the action is similar). I can't see that
having a bidirectional link is that important although could be useful
in the future.

I had been hoping that I could just load the 27MHz (If that's what it
is) RC control straight onto the video signal. How naive is that?

Thanks again. Any further assistance always welcomed.

Flint
 
M

martin griffith

Jan 1, 1970
0
Thanks Martin.

As you may have gathered, I am not skilled in the art (or mystery) of
electronics (I am a mechanical guy) and will need to gather more info
and assistance on taking this further. One issue is going to be cost
but I guess there are some pretty cheap micros or PICs about that
could be considered.

The other issue is going to be how effective the data speed will be
given that I am trying to control something dynamic (it's not a
vehicle or airplane but the action is similar). I can't see that
having a bidirectional link is that important although could be useful
in the future.

I had been hoping that I could just load the 27MHz (If that's what it
is) RC control straight onto the video signal. How naive is that?

Thanks again. Any further assistance always welcomed.

Flint
you could feed the 27MHz into the video feed, but i can't really
suggest an optimal method.
Notch filters may be rquired to prevent it upsetting the video.

But back to basics:

How fast is the data going, I dont know much about RC protocols, and
i'm too lazy to google


martin
 
J

John Barrett

Jan 1, 1970
0
flint said:
Thanks Martin.

As you may have gathered, I am not skilled in the art (or mystery) of
electronics (I am a mechanical guy) and will need to gather more info
and assistance on taking this further. One issue is going to be cost
but I guess there are some pretty cheap micros or PICs about that
could be considered.

The other issue is going to be how effective the data speed will be
given that I am trying to control something dynamic (it's not a
vehicle or airplane but the action is similar). I can't see that
having a bidirectional link is that important although could be useful
in the future.

I had been hoping that I could just load the 27MHz (If that's what it
is) RC control straight onto the video signal. How naive is that?

Thanks again. Any further assistance always welcomed.

Flint

Didnt you say "video feedback" ?? so RC to the equipment, video back from
the equipment ?? you cant piggyback the RC data on the video that way if the
signal sources are at opposite ends of the cable :)

Get a camera with modulated channel 2/3 output, and make sure your RC is
running on a VERY different freqency.... you said 27mhz RC ?? thats far
enough away from TV freqencies at 54 to 66 mhz for channels 2/3

setup low-pass/high-pass filters at each end to isolate the RC/video signals
... you will probably need to attenuate the RC signal a LOT since its
designed for over the air rather than wireline. Set the frequency split at
about 40-45 mhz -- dont have to be horribly accurate, nor do you need a
filter with sharp roll-off. The technique is called duplexing and ham radio
repeaters do the same thing so they can transmit and recieve at the same
time over a single antenna.. there are lots of online resources including
applets that will design the filters for you.

you could even feed DC power over the same coax along with the video/rc
signals if you like :) an inductor at each end to block the RF from the DC
powered circuits, and a capacitor to couple the RF to/from the coax
 
R

Rich Grise

Jan 1, 1970
0
Hi All,

A question for you clever guys and gals -

I am using a conventional radio control unit (as used for model
planes) to activate servo motors in an experimental setup. This works
well but I now want to add video feedback from a camera. Radio control
is really not a preferred option for me in this appllication and to
keep the overall system simple, a cable would actually be better. The
separation diistance is about 200ft. The cable needs to be as small as
possible.

Is it possible to achieve all of the communications including video
down just a single co-ax? By this I guess I mean can either of these
work? -

A) A single co-ax cable carrying the video but could I somehow 'add
in' the modulated RC control i.e. get rid of the aerial at each end
and suppliment the transmitter and reciever with some electronic
interface to make the direct cable connection. Would the modulated RC
signal screw up the video or visa-versa?

B) Could I achive the same effect but not using the RC unit. i.e.
again by adding a modulated control signal to the video conection.

In order to keep the cable simple, cheap and lightweight, I don't
really want to go for a more conventional video plus RS422 twin
screened twisted pairs setup.

Your comments, and any recommendations, humbly recieved.

From what you've described, it's absolutely doable, with the right
kind of support circuitry at each end. For example, you'd modulate
your video onto some carrier and apply that at the camera end, and
modulate your RC control onto some other carrier and apply that
at the control end, with suitable filters and demodulators at the
corresponding other end.

It does sound like a project of some magnitude, however. :)

Good Luck!
Rich
 
R

Rich Grise

Jan 1, 1970
0
On 26 Mar 2007 05:52:46 -0700, in sci.electronics.design "flint"
you could feed the 27MHz into the video feed, but i can't really
suggest an optimal method.
Notch filters may be rquired to prevent it upsetting the video.

But back to basics:

How fast is the data going, I dont know much about RC protocols, and
i'm too lazy to google

I just can't restrain myself:

TV rcvr-<-[TV filter]-<-+ +-<-[TV filter]-[TV xmtr]-<-Camera
+--cable--+
RC xmtr->-[RC filter]->-+ +->-[RC filter]-[RC rcvr]->-Servos

All you need is somebody to design the stuff for you, or tell you what
you need to buy. :)

And just FYI, RC protocol is almost audio, so no worries. :)
(I once had to generate servo control signals for a robot, and so I
went down to Futaba and asked the tech. It's something like a 1-20
ms pulse at a 100 ms period, or something way slow like that. Please
don't quote my numbers!)

Good Luck!
Rich
 
M

martin griffith

Jan 1, 1970
0
I just can't restrain myself:

TV rcvr-<-[TV filter]-<-+ +-<-[TV filter]-[TV xmtr]-<-Camera
+--cable--+
RC xmtr->-[RC filter]->-+ +->-[RC filter]-[RC rcvr]->-Servos

All you need is somebody to design the stuff for you, or tell you what
you need to buy. :)

And just FYI, RC protocol is almost audio, so no worries. :)
(I once had to generate servo control signals for a robot, and so I
went down to Futaba and asked the tech. It's something like a 1-20
ms pulse at a 100 ms period, or something way slow like that. Please
don't quote my numbers!)

Good Luck!
Rich
Some days you just can't see the wood for the trees


martin
 
F

flint

Jan 1, 1970
0
From what you've described, it's absolutely doable, with the right
kind of support circuitry at each end. For example, you'd modulate
your video onto some carrier and apply that at the camera end, and
modulate your RC control onto some other carrier and apply that
at the control end, with suitable filters and demodulators at the
corresponding other end.

It does sound like a project of some magnitude, however. :)

Good Luck!
Rich

Thanks for all the suggestions everyone. I was trying to establish if
it was possible and I think you have confirmed that.

I shall be speaking to an electronic design guy I know to see if he
can knock something up for me.

Question - If control functionality such as this can be added to video
on a co-ax, why is the norm to provide a dedicated video plus either
RS232 or RS422 on twisted pairs?.

Thanks

F
 
J

john jardine

Jan 1, 1970
0
flint said:
Thanks for all the suggestions everyone. I was trying to establish if
it was possible and I think you have confirmed that.

I shall be speaking to an electronic design guy I know to see if he
can knock something up for me.

Question - If control functionality such as this can be added to video
on a co-ax, why is the norm to provide a dedicated video plus either
RS232 or RS422 on twisted pairs?.

Thanks

F

I'd be thinking maybe the twisted pair is about 1000X simpler and cheaper?.
(wouldn't want to knock one up without a customer underpinning the week's
work :)
 
R

Rich Grise

Jan 1, 1970
0
[about video and RC on one cable in opposite directions]
Didnt you say "video feedback" ?? so RC to the equipment, video back from
the equipment ?? you cant piggyback the RC data on the video that way if the
signal sources are at opposite ends of the cable :)

Why not, exactly?

Thanks,
Rich
 
R

Rich Grise

Jan 1, 1970
0
Thanks for all the suggestions everyone. I was trying to establish if
it was possible and I think you have confirmed that.

I shall be speaking to an electronic design guy I know to see if he
can knock something up for me.

Question - If control functionality such as this can be added to video
on a co-ax, why is the norm to provide a dedicated video plus either
RS232 or RS422 on twisted pairs?.

Probably because it's simpler. You could have baseband video on the
cable, and ordinary RS*** on a pair, so you don't need any modulators
or demodulators or filters. :)

Cheers!
Rich
 
J

joseph2k

Jan 1, 1970
0
flint said:
Hi All,

A question for you clever guys and gals -

I am using a conventional radio control unit (as used for model
planes) to activate servo motors in an experimental setup. This works
well but I now want to add video feedback from a camera. Radio control
is really not a preferred option for me in this appllication and to
keep the overall system simple, a cable would actually be better. The
separation diistance is about 200ft. The cable needs to be as small as
possible.

Is it possible to achieve all of the communications including video
down just a single co-ax? By this I guess I mean can either of these
work? -

A) A single co-ax cable carrying the video but could I somehow 'add
in' the modulated RC control i.e. get rid of the aerial at each end
and suppliment the transmitter and reciever with some electronic
interface to make the direct cable connection. Would the modulated RC
signal screw up the video or visa-versa?

B) Could I achive the same effect but not using the RC unit. i.e.
again by adding a modulated control signal to the video conection.

In order to keep the cable simple, cheap and lightweight, I don't
really want to go for a more conventional video plus RS422 twin
screened twisted pairs setup.

Your comments, and any recommendations, humbly recieved.

Thanks

F
Easy to do, if you understand what to do. There is endless combinations on
what you can do. Bandsplit is just the start, directional couplers and
tx/rx bridging add to the things that can be done. You can sucessfully
send power one way, voice, data, and video both ways all at the same time.

Just the same, i would have just used used an additional RF link for the
video, just like the RC flyers do.
 
J

John Barrett

Jan 1, 1970
0
Rich Grise said:
[about video and RC on one cable in opposite directions]
Didnt you say "video feedback" ?? so RC to the equipment, video back from
the equipment ?? you cant piggyback the RC data on the video that way if
the
signal sources are at opposite ends of the cable :)

Why not, exactly?

Thanks,
Rich

because if I understand correctly -- the video is sourced from the
operational equipment end of the proposed cable -- and the RC is sourced
from the control at the opposite end -- you dont have both signal sources at
the same end to combine them

also -- RC is a continuous signal -- would be a huge problem to pick up the
signal from the RC transmitter and convert it to something that can be
combined with the video signal -- would be better off sticking the RC on an
audio subcarrier IF the RC signal and video were sourced at the same end of
the cable -- but that doesnt appear to be the spec -- RC to equipment, video
feedback from equipment
 
R

Rich Grise

Jan 1, 1970
0
Rich Grise said:
[about video and RC on one cable in opposite directions]
Didnt you say "video feedback" ?? so RC to the equipment, video back from
the equipment ?? you cant piggyback the RC data on the video that way if
the
signal sources are at opposite ends of the cable :)

Why not, exactly?

because if I understand correctly -- the video is sourced from the
operational equipment end of the proposed cable -- and the RC is sourced
from the control at the opposite end -- you dont have both signal sources at
the same end to combine them

But, on what do you base your assertion that both signal sources _MUST_
be at the same end? Did you miss my diagram?

TV rcvr-<-[TV filter]-<-+ +-<-[TV filter]-[TV xmtr]-<-Camera
+--cable--+
RC xmtr->-[RC filter]->-+ +->-[RC filter]-[RC rcvr]->-Servos

The RC signal is going from left (your end) to right (the remote end),
and the TV signal is going from right to left. Can you come up with
some kind of physics that proves that that's impossible?

Thanks,
Rich
 
J

John Barrett

Jan 1, 1970
0
Rich Grise said:
Rich Grise said:
On Mon, 26 Mar 2007 15:29:06 +0000, John Barrett wrote:

[about video and RC on one cable in opposite directions]

Didnt you say "video feedback" ?? so RC to the equipment, video back
from
the equipment ?? you cant piggyback the RC data on the video that way
if
the
signal sources are at opposite ends of the cable :)

Why not, exactly?

because if I understand correctly -- the video is sourced from the
operational equipment end of the proposed cable -- and the RC is sourced
from the control at the opposite end -- you dont have both signal sources
at
the same end to combine them

But, on what do you base your assertion that both signal sources _MUST_
be at the same end? Did you miss my diagram?

TV rcvr-<-[TV filter]-<-+ +-<-[TV filter]-[TV xmtr]-<-Camera
+--cable--+
RC xmtr->-[RC filter]->-+ +->-[RC filter]-[RC rcvr]->-Servos

The RC signal is going from left (your end) to right (the remote end),
and the TV signal is going from right to left. Can you come up with
some kind of physics that proves that that's impossible?

Thanks,
Rich

what have I been saying from my first post ?? every one else has been
talking about embedding the RC signal in the video
 
J

jasen

Jan 1, 1970
0
Hi All,

A question for you clever guys and gals -

I am using a conventional radio control unit (as used for model
planes) to activate servo motors in an experimental setup. This works
well but I now want to add video feedback from a camera. Radio control
is really not a preferred option for me in this appllication and to
keep the overall system simple, a cable would actually be better. The
separation diistance is about 200ft. The cable needs to be as small as
possible.

They do that with stinger missiles, using a very thin coax.
Is it possible to achieve all of the communications including video
down just a single co-ax?
definately.

A) A single co-ax cable carrying the video but could I somehow 'add
in' the modulated RC control i.e. get rid of the aerial at each end
and suppliment the transmitter and reciever with some electronic
interface to make the direct cable connection. Would the modulated RC
signal screw up the video or visa-versa?
B) Could I achive the same effect but not using the RC unit. i.e.
again by adding a modulated control signal to the video conection.

both could work.

ordinary video occupies a basically the frequencies from 0 to 5Mhz
anything above that is available for signalling.

Bye.
Jasen
 
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