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Generating Video Sync Pulses

Can anyone advise me on where to find information on generating video sync pulses for PAL television systems, without using PIC chips?

The basic aim of the project I am working on is to take an analog voltage from a sensor, convert it to a bcd number and then display that number on a TV screen.

To start with I tried using a NOR gate astable (CMOS) to generate the horizontal sync pulses, but I may try a counter instead as that will hopefully be more accurate.

In order to generate the vertical sync signal, I have read that I can just send out 20 blank video lines with the horizontal sync inverted. Is this correct? (I would prefer to use non-interlaced display if possible)

The signal I need to generate is a standard composite video signal (So I don't need to encode it for transmission).

I did look into the possibility of using a sync signal generator chip, but the only one I could find (from Fairchild I believe) is far too complex for my needs.

Reply to
Robert Knight
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"Without using PIC chips"? Where did that come from? Whassa madda widda PIC?

A crystal and counter arrangement will be much more stable than an analog oscillator. The standard itself is pretty strict about accuracy, and some sets can be sensitive to variations. There are some "magic frequencies" that will let you derive the line and field rates with integer dividers, and will give you nice pixel clocks in the bargain -- you may want to take a look.

But why _not_ use a PIC here?

This would probably work. You're diverging from the standard so YMMV. If you use a PIC for this then you can make it interlaced fairly easily.

If it's easy to use why not go for it?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply to
Tim Wescott

Hi Robert,

In the old days (80's) I used to take a sync chip for that. Many of them had the capability, in the absence of any sync pulses that they could detect, to generate their own so that the TV set or VCR wouldn't go haywire and that the VCR could produce a clean blank image or some on-screen message when the tape was stopped. The ones for VCRs produced a slew of other signals, too..

I don't know if these are still made but it could be worth a Google search. Mine were mostly from Philips but these older versions are pretty much all obsolete I believe. Things become obsolete very quickly in consumer land. As far as I remember the part numbers began with SAA. Nowadays. I'd check Japanese companies as well.

Chip solutions will be the easiest. Once I had to make a PAL design NTSC compatible but wasn't told so when the project began. As luck had it, all I had to do is ground one of its pins and, voila, it went to the US standard for H-sync, blanking, V-sync etc. It blew the client away when the 'extra billed time' for this modification amounted to around 15 minutes. Their folks provided the logic signal for the action and all I added was a little FET.

Regards, Joerg

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Reply to
Joerg

Hi Robert,

The SAA1043P from Philips was a great chip for doing this kind of thing, it can generate a fully interlaced sync pulse and a host of other video timing signals with just a couple of other components. Very probably obsolete now however.

Philip

Reply to
Electric dabbler

Hi Philip,

That one used to be my favorite chip. But last time I checked it seems to be gone. Sigh. Maybe the EL5483 could be coaxed into a similar function. At least it can produce a default V-sync in the absence of a properly detected signal.

Regards, Joerg

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Reply to
Joerg

Thanks Philip,

Fortunately I managed to find just such a chip. The reason I cannot use PIC is as this is an A-Level electronics project, and marks are awarded for use of hardware rather than software.

Regards, Robert.

Electric dabbler wrote:

thing, it

timing

obsolete now

Reply to
RobK

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