Frequency for Sawtooth wave oscillator for both horizontal and vertical deflection

[sztibi82]

Hi all.
i want to build a Sawtooth wave oscillator for both horizontal and vertical deflection. Please can tell me somebody on what frequencys are they. Also if someon has a schematic pls post the link here.

Thanks

 

[echo47]

Tv oscillator

Are you talking about television? Which video format?

 

[slavko]

Re: Tv oscillator

maybe this will help you https://www.serasidis.gr/circuits/colour_bar_gen/colour_bar_gen.htm

 

[VVV]

Re: Tv oscillator

Can I ask what you are trying to achieve?
Sawtooth generators are easy to build, but if you are thinking about television sets, then remember it is the currents through the deflection coils which are approximately sawtooth-shaped.
Anyway, a better description of the application would help.

 

[sztibi82]

Re: Tv oscillator

Hi guys. Thanks for the answers.

It is a school project. I have to make 2 oscillators(horizontal and vertical).Also i have to design an equipment which has to have as input the 2 oscillators, and a voltage, and as output complex video signal. Depending from that voltage, it has to change the grayscale.
It has to bedone uding the above descriptions.

 

[echo47]

Tv oscillator

There are dozens, maybe hundreds of different video formats in the world. You must give more information. Are you talking about ordinary broadcast television, computer display, slow-scan video, machine vision, or what?

If broadcast television, then is it PAL, NTSC, SECAM, or something else? Or tell us which country you are in.

I've never heard of "complex video". Maybe you mean "composite video".

 

[VVV]

Re: Tv oscillator

The sawtooth oscillators make a little bit of sense when you are talking about grayscale. But what about that third voltage that has to "change the grayscale". What does that mean? Change from vertical grayscale to horizontal one, or change the contrast, or what?

I am assuming this will be a B/W television signal, am I correct?
But which standard does it have to comply with?

 

[sztibi82]

Re: Tv oscillator

Hi all.

Yea, it is B/W signal;. The output has to be composite signal. With the 3th voltage you alter the contrast.

 

[VVV]

Re: Tv oscillator

For B/W, if the signal is supposed to be NTSC compatible, the frequencies are 15750Hz for horizontal, 60Hz for vertical.
For PAL and SECAM, use 15625Hz and 50Hz respectively.

You will need more than just the two oscillators to build what you need, namely synch pulses and a way to control the contrast.
What components are you allowed to use?

 

[sztibi82]

Re: Tv oscillator

It has to be PAL, while i am in Romania. I am free to use whatever component i desire.

 

[echo47]

Tv oscillator

This sounds like a student design project. Are you expected to create a fully analog design? You will need a pretty stable horizontal oscillator. A video signal is best created with a crystal oscillator and digital logic.

How closely do you need to follow the PAL video timing specification? Is it acceptable to build a crude circuit that just barely works on a video monitor? You could do that with a few 555 timers and some mixing logic.

How about using a video sync generator chip (if you can find one that hasn't been discontinued)? Of course, that would take all the challenge out of the project.

 

[sztibi82]

Re: Tv oscillator

Can you please recomend some ICs. I want to build it as easy as possible, and as good, stable as i can. I have to receive mark for it, so it is important.

 

[VVV]

Re: Tv oscillator

One more thing: what is the grayscale supposed to look like? Horizontal or vertical? Or a combination? The latter would be the hardest. Any of the other two would be relatively easy.
I will try to post something for you. Meanwhile, here is the basic idea: you build a 1MHz crystal oscillator, follwed by a divide by 64 counter. That will give you the horizontal synch pulses. Divide that by 625 and you get the vertical synch pulses. Note that this system will only produce 312 lines, instead of 625, so it will be non-interlaced, but it will work very nicely and it will be much easier to build.

Use intermediate signals from the divider and AND them with synch pulses to obtain the correct synch pulse widths and blanking signals. The two synch signals should be XORED together to achieve the composite synch signal, which will in fact "chop" the vertical synch pulse, as required. You will not need any pre-equalization, nor post-equalization pulses. Remember, this is non-interlaced video.

To achieve the grayscale, build one (or two) sawtooth generator, using simply a constant current source that charges up a capacitor. The blanking pulses will be used to discharge the cap (basically short it to GND). That way, the sawtooth is synchronized with the synch pulses (it should be clear by now why I say only one grayscale is easiest to achieve).
The control voltage will be used to actually adjust the current that charges up the capacitor. The capacitor only charges between the blanking pulses (recall that the blanking pulses discharge the cap). So, depending on how fast the cap charges, the amplitude of the voltage at the end of the interval will be higher or lower, resulting in a different contrast. So use the third control voltage to actually vary the cap's charging current and you achieve linear contrast control.

Finally, combine all these elements (ramp, blanking, synch pulses), using resistors (and transistors possibly) and you will have your generator. The final amplitude of the video signal should be 1Vpp (the standard amplitude). Then you can test it by feeding it to your VCR video input and viewing it on your TV.

 

[sztibi82]

Re: Tv oscillator

I gona build it, and post the results.
Thanks

 

[VVV]

Re: Tv oscillator

I have to make a corection to the previous post: to obtain the vertical sync pulses, divide the horizontal frequency by 312, not 625. Sorry about that.
VVV

 

[echo47]

Tv oscillator

Don't XOR hsync with vsync. That causes the hsync leading edge to occur at the wrong time. It's better to simply omit hsync for a few lines.