How to generate synchro signal for CVBS TV signal

[Pitbuell94]

Hi everybody,

I'm trying to make a video scaler using normal video signal PAL or SECAM 625 horizontal lignes at 50 frames per second and convert it to an other format but always for Cathodic TV.

In fact, my hobby is to repair very old TV using vaccum tubes technologie.
So, I repair actually olds tv with 819 lignes definition.

The problem here is there is no more TV emetter with this kind of resolution so I need to make a brand new one to run again my old TV.


Just for your information, in France René Barthélemy develops the definition of 819 TV lines. During the years of occupation, in 1944, Barthelemy reached 1015 and even 1042 lines in Black and White.


All these TV from stoneage are in black and white.

So my idea is first to take the video signal( CVBS) PAl or SECAM, to keep out the colour with analog filter ( CHROMA information at 4.43 MHz), to convert this B&W video signal with a TDA 8708 > obtain a 8 bit luminance information> make calculation of missing lines and convert again in CVBS signal.

All the synchro signal come from a TDA1881.

My problem is that the scan rate is different between the 2 standarts.

IN video signal is 625 lines @50Hz
OUT video signal is 819 lines @50Hz.

First, to be sure my Spartan 3E-500 is able to do it, I just want to make a test and not directly design a full video converter.

I just want to sent to my B&W tv a signal with black and white horizontal and vertical stripes.

See photos.

Does someone try to do a soft to drive actual TV with video signal?

Thanks for your comments.

Pitbuell94.

 

[farhada]

Do you have any spec for that, I can give you some code, I was the person responsible for the TV IP of TI's OMAP series TV encoder and have years of experience in this, but never heard of the 819 line definition.

Cheers,
/Farhad

Added after 29 minutes:

If you want to drive the TV signals with a pattern, I can create a simple code for you, I had done it on a CPLD for TV testing purpose, it is quiet simple. But if you want to capture the picture from an outside source and show it on the new one, then it is a whole different story and it is MUCH more difficult.

 

[Pitbuell94]

Hi Farhada,

Thank you for your reply.

To test my TV, I want first check the possibility of my NEXYS2 to be able to generate and send a patter to my TV.

Next step is to realize a real time video scaler to test the great quality of these first HD TV in black and white standart.

For your information, have a look at this forum >

**broken link removed**

I repair for my hobby old electronic with tube technologie.

Actually, I send a video signal based on SECAM 625lines french standart and the result is the image on the screen is not good because the line frequency is 15625 in place of 20475> the hight voltage of CRT is running like a switch power supply drive by the video signal so because the frequency is too low, white colour are grey and focus is bad and the rest too...

The full image have 819 lines in two frames at 50Hz.

Real effectives line are 737 visibles lines.

There is by frame 1 field of 41 lines called Fiel blanking period.
the field synchro pulse is 20 µS.
Frame period is 40mS.
Field period is 20mS.
top synchro line is 2.5µs.
Back porch is 5µs.
Front porch is 0.5µs
There is around 1200 pixels per lines but a range between 360 to 720 is enought.
There is 2 half video ligne at begin and end of frame because it's interlaced image.

I hope I do not disturb you too much with this.

Thank you very much for your help.

Pitbuell94.

 

[farhada]

Hi Pitbuell94,
Thank for the info, I did some search about this and it is pretty amazing. How sad they could not get this one to become the standard for the TV broadcasting back in the 50s, the world would have looked different today
Is the signal identical to the normal CVBS signal otherwise?

The timing is not a big issue, I can give you the code by the end of the week, it is fun to make it, but I am afraid I will not have any way of testing it other than simple simulation.

What I can give you a simple pattern generator to create 2-3 different standard B&W patterns for the spec you sent here, you can trim the code and change it if you want. Part of this code is copyrighted so I really appreciate it if you do not share the code with others when I send it to you.

Cheers,
/Farhad

 

[Pitbuell94]

Hi Farhada,

This is exactly the form of the signal.

Have a look on this.

**broken link removed**

In this document, I' m interesting by the french standart.

In the Belgium standart, there is more visibles lines.

Here there is all the information concerning timing.

If you want, I can send you the code I make > don't be afraid: it's my first attempt.

Just to generate timing and not a patter or something else: to make a simulation.

this code is not finish at this time.

If you have some code, I'll appreciate to have a look on it.

I start on the past century with BASIC, ASSEMBLEUR and TURBO PASCAL.

This is for personnal use.

Is-it possible to make a pattern from a phot or jpeg, gif file or something else?

As soon this run, I'll make a video or photo to you.

Than you very much.

Pitbuell94.

 

[farhada]

Excellent,
Thanks for the link, I will look into it and get back to you when I have the code. Adding an image makes the code more complicated, but it is possible to burn the image in EEPROM and then load it during execution, will see how far I can get with this in a few days I have over.

cheers,
/Farhad

 

[Pitbuell94]

Hi Farhada,

Thank you.

Today I'm trying to flash my NEXYS2 with XILINX ISE WEBPACK.

I spent a week to try to do it with ACTIVE HDL without any success.

Do you want I sent you my first code just to get afraid?

Have a nice day.

Pitbuell94.

 

[Pitbuell94]

Hi all,

My code run fine in NEXYS2 by driving the leds.

I just now need an monitor to test it in place of my oscilloscope.

Next step is to add code to make a proper video signal in place of signal to drive video monitor.

Pitbuell94.

 

[Pitbuell94]

Hi All,

This is the simulation of my design.

Everything work fine with right timing.

This code generate a complete black screen > this is just to test the synchro signal is ok.

Next step is to add black and white stripes and very later (don't forget I'm a newbee), make a complete real time scaler.

Simulations are done with ISIM ISE webpack 11.

In yellow, this is the cvbs signal with the top line number from 0 to 818.

Others signals are HSync, Vsync, Videon.

This signal match with this standart : **broken link removed**

Have a good day.

Pitbuell94.

 

[IanP]

Here is a post on how to generate a video signal with AT89S2313 microcontroller and 17-and-something-MHz clock ..

Just different approach, that’s all ..

Rgds,
IanP

 

[Pitbuell94]

Hi Dear Gentleman,

Your idea is a good idea.

My first idea was to build a simple test pattern generator to test my old B&W TV.

Watching TV with only B&W stripes during long period is not a very good idea because after long time, yours eyes are burned like TV CRT tube on the airport .

So, at the beginning of my project, I think about small IC like yours, but, later, I think it would be a greater idea if I could made a real time video scaler to watch these TV in continuous time.

I keep in mind yours idea because with this system I can quicly check my TV.

My last idea is to convert FULL HD TV signal (1080 lignes) to 819.

Actually, I try to convert video SECAM 625 lignes to 819 B&W > in fact, the quality is the same because native definition is worst than the final format.

I just make an average between adjacent lines.

Have a good day.

Pitbuell94.