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Composite video issue
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Ultron81:
OK, I was a little confused when you originally asked the question and thought maybe you were talking about the output from an RF demodulator.

So you are looking at pin 13 (chroma carrier) right? What are you trying to do? Use the RF modulator (LM1889 in particular) as a video encoder for composite video? There are tons of ICs that would be better in that case, and may give you a better signal as well. In fact, if you already have access to the chroma and luma signals, you can buffer the 2 signals with the THS7314, then connect the chroma to the luma with a 470pF cap and use that as your composite video.

Well, anyway, if you plan on using pin 13, the only way you are getting composite video is if the luma is applied to that pin as well. Look at the application circuit I attached (from the LM1889 data sheet).

Can you tell us what the RF modulator is from (i.e. video game console)? There may be other ways to get the composite signal than going from the RF modulator.

EDIT: Oh, just saw getting the signal another way would be no dice. Still, would be good to know where it is from so I can see the rest of the video circuit.
maginnovision:

--- Quote from: Ultron81 on January 14, 2019, 05:13:38 am ---OK, I was a little confused when you originally asked the question and thought maybe you were talking about the output from an RF demodulator.

So you are looking at pin 13 (chroma carrier) right? What are you trying to do? Use the RF modulator (LM1889 in particular) as a video encoder for composite video? There are tons of ICs that would be better in that case, and may give you a better signal as well. In fact, if you already have access to the chroma and luma signals, all you need is a 470pf cap tied between the chroma line and luma line, and the buffer circuit with the THS7314.

Well, anyway, if you plan on using pin 13, the only way you are getting composite video is if the luma is applied to that pin as well. Look at the application circuit I attached (from the LM1889 data sheet).

Can you tell us what the RF modulator is from (i.e. video game console)? There may be other ways to get the composite signal than going from the RF modulator.


--- End quote ---

It's a little complicated. It is from a video game console and I don't actually have direct access to pin 13 of the LM1889 but it is routed to a pin on a 50 pin expansion port. I have access to both the luma and the composite signal encoded by the modulator. What I don't have is the chroma clock but I do have it 180 inverted and hor/vert drive signals. I also do NOT have b-y or r-y. That's the reason it's not ideal but I can't do much about it. It's also still better than the only other built-in option, RF.

EDIT: Almost all of the video is done in some custom IC's(no good data) that generate r-y, b-y, luma, hor/vert drive. Chroma is just split off from clock circuit.

EDIT 2: The RF modulator gets -5V, +10V, +2.5V, audio, chroma, luma, b-y and r-y.
vk6zgo:

--- Quote from: Ultron81 on January 14, 2019, 05:13:38 am ---OK, I was a little confused when you originally asked the question and thought maybe you were talking about the output from an RF demodulator.

So you are looking at pin 13 (chroma carrier) right? What are you trying to do? Use the RF modulator (LM1889 in particular) as a video encoder for composite video? There are tons of ICs that would be better in that case, and may give you a better signal as well. In fact, if you already have access to the chroma and luma signals, you can buffer the 2 signals with the THS7314, then connect the chroma to the luma with a 470pF cap and use that as your composite video.

Well, anyway, if you plan on using pin 13, the only way you are getting composite video is if the luma is applied to that pin as well. Look at the application circuit I attached (from the LM1889 data sheet).

Can you tell us what the RF modulator is from (i.e. video game console)? There may be other ways to get the composite signal than going from the RF modulator.

EDIT: Oh, just saw getting the signal another way would be no dice. Still, would be good to know where it is from so I can see the rest of the video circuit.

--- End quote ---

You & I have got "caught out" by mistakes in the drawings in the data sheet.
On page (1), pin 12  is shown as  "video input", & pin 13 as "chroma subcarrier".

On page (4), pin 12 is labelled "video bias" & pin 13 is "video input".

On page (6), pin 12 becomes "sound carrier input" &  pin 13 is still "video input"---"chroma subcarrier" seems to have disappeared!

"Moving right along" to page (7), the "TV Game Schematic", pin 12 goes back to being "video input".
Pin 13 has no identification, but is connected to the -9v supply via a 2k resistor!

Finally, page (9), in fig (1) shows the connection you posted in his last posting.
Pin 12 is now "DC reference voltage", pin 13 is "luminance & sync input".
No explanatory notes for that one, at all!

Aaaaarrrrgggghhh!, |O
vk6zgo:
Thinking over it, there is a vague hint of an explanation on page 8.
It seems that the luma & chroma are passively added in the 2k resistor.

It does seem to look as if there is no blanking of the subcarrier during the blanking interval, or, it seems, any provision of colour burst, so the TV or monitor relies upon locking to the, always present, chroma subcarrier.

This would account for the presence of "noise" upon  the syncs in the screenshots from the OP.

I really expected these chips to be able to produce standard video, rather than a rather primitive kluge.
The circuits in VCRs seem to be able to do so!
Benta:
Be very careful with the old video chips from National (TI). There are deliberate mistakes in the data sheets, both LM1881 and LM1889. I believe it stems from the VCR times, where Macrovision exerted pressure to keep amateurs from using the chips for copy protection removal. "Legitimate" users would get an amended data sheet under NDA.
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