I've got a question.
Does anyone know of a circuit that can take the vertical or horizontal sync pulse from a VGA signal and generate a sawtooth waveform?
I've got a project where I am wanting to display a VGA signal on a Tektronix XY display and want to have at least two resolutions.
720 X 576 for 5:4 displays and 800 X 600 for 4:3 displays.
The idea is I want the sawtooth waveforms to automatically switch frequencies if possible.
I could even use a switch to select two frequencies if need be, however I need to know what those frequencies need to be.
I've got a Leitch FR-684 video distribution frame that can hold 10 cards and two have daughter boards that plug in and I was going to use those two for the sawtooth generation and a third for the video as the output from the card will have the proper levels so that the displayed image looks its best.
Does anyone know of a circuit that can take the vertical or horizontal sync pulse from a VGA signal and generate a sawtooth waveform?
I've got a project where I am wanting to display a VGA signal on a Tektronix XY display and want to have at least two resolutions.
720 X 576 for 5:4 displays and 800 X 600 for 4:3 displays.
The idea is I want the sawtooth waveforms to automatically switch frequencies if possible.
I could even use a switch to select two frequencies if need be, however I need to know what those frequencies need to be.
I've got a Leitch FR-684 video distribution frame that can hold 10 cards and two have daughter boards that plug in and I was going to use those two for the sawtooth generation and a third for the video as the output from the card will have the proper levels so that the displayed image looks its best.
You need XYZ mode (intensity modulation), not just XY. The usual approach to sawtooth is constant current source into an integrator and reset the integrator with the relevant pulse. The simplest integrator is just a capacitor to ground.
At different frequencies the waveform will have different amplitude unless you can program the current source.
At different frequencies the waveform will have different amplitude unless you can program the current source.
So I found this site that lists the timing and frequencies for various VGA resolutions.
http://martin.hinner.info/vga/timing.html
The only thing I can think of doing is get a VGA to BNC cable then seeing if I have two function generators at work that can produce a sawtooth and have an external sync. That way I can set the sawtooth generators to the listed frequencies, set the resolution in Windows to the desired resolution and see how well it works.
The two resolutions I need 720 X 576 and 800 X 600 both according to the resolution settings in Windows 11 can have a refresh rate of 75Hz.
For 800 X 600 the horizontal frequency listed on that site is 53.7kHz. Given 720 X 576 is real close, I'd be willing to bet that frequency would work for both resolutions.
So I'd need a simple sawtooth generator that is accurate with one oscillator set for 75Hz and the other set for 53.7kHz that has a sync input. I'd use trimpots to allow for varying the frequency for tweaking things properly.
http://martin.hinner.info/vga/timing.html
The only thing I can think of doing is get a VGA to BNC cable then seeing if I have two function generators at work that can produce a sawtooth and have an external sync. That way I can set the sawtooth generators to the listed frequencies, set the resolution in Windows to the desired resolution and see how well it works.
The two resolutions I need 720 X 576 and 800 X 600 both according to the resolution settings in Windows 11 can have a refresh rate of 75Hz.
For 800 X 600 the horizontal frequency listed on that site is 53.7kHz. Given 720 X 576 is real close, I'd be willing to bet that frequency would work for both resolutions.
So I'd need a simple sawtooth generator that is accurate with one oscillator set for 75Hz and the other set for 53.7kHz that has a sync input. I'd use trimpots to allow for varying the frequency for tweaking things properly.
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Here's what I'm thinking.
I've got three of these boards.
Two have daughterboards and one does not.
I would remove the daughter boards from the two, cut some perfboard to fit the size then put the vertical sawtooth generator on one and the horizontal sawtooth generator on the other.
Now both have jumpers on the inputs to select AC or DC coupling so what I'll do is use that to send the sync signal to the sawtooth generators on the daughterboard then the signal will be picked off and sent back to the jumper connection so that the amp circuitry can be used to control the sawtooth amplitude.
I may include a trimpot on the daughterboard just so I can be able to reduce the output if it's too high for the amp circuitry on the card.
The board sends +/- 8Vdc to the daughterboard so that would power the OP-AMP buffer and sawtooth generator. The buffer would need to drive a 75 ohm load given the input impedance of the board is 75 ohms.
I could send the sync signals through the circuitry that is before the daughterboard as that would be easiest, but I don't know how the circuitry would do with the sync pulses. I suppose since it is meant for NTSC video signals it should pass sync pulses just fine.
I've got three of these boards.
Two have daughterboards and one does not.
I would remove the daughter boards from the two, cut some perfboard to fit the size then put the vertical sawtooth generator on one and the horizontal sawtooth generator on the other.
Now both have jumpers on the inputs to select AC or DC coupling so what I'll do is use that to send the sync signal to the sawtooth generators on the daughterboard then the signal will be picked off and sent back to the jumper connection so that the amp circuitry can be used to control the sawtooth amplitude.
I may include a trimpot on the daughterboard just so I can be able to reduce the output if it's too high for the amp circuitry on the card.
The board sends +/- 8Vdc to the daughterboard so that would power the OP-AMP buffer and sawtooth generator. The buffer would need to drive a 75 ohm load given the input impedance of the board is 75 ohms.
I could send the sync signals through the circuitry that is before the daughterboard as that would be easiest, but I don't know how the circuitry would do with the sync pulses. I suppose since it is meant for NTSC video signals it should pass sync pulses just fine.
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