VGA scan conversion alternatives

[Logistics]

Re: VGA scan conversion alternatives

First, that document in the first post comes up empty for me, unless I edit it in a dos box and then it contains a few words but mostly jargon.

From what I'm seeing online about the VFX1, it accepts normal VGA. But you seem to believe it has to be converted to something other than VGA. If it still uses RGB + Sync whether it's H+V or Composite Sync, it could only be converted to PAL or NTSC if anything other than VGA, right? Which would be 31kHz scan rate versus 15kHz scan rate, respectively.

But again, from what I'm reading, the VFX1 uses only VGA hookups. This leads me to believe that the box you're trying to build is nothing more than a couple of LCD drivers combined with some sort of re-distribution for the RGB + H/V Sync. I don't think you can run two monitors off the same hookup so this box probably contains some form of repeaters.

The Televiewer page I saw didn't mention any RGB output, only Composite and S-Video. I saw a mention of VGA throughput, but no PAL/NTSC RGB output.

[pentium]

Re: VGA scan conversion alternatives

Uh oh, UH oh, UH OH!
AAAAAAAAAAAAAA!!
Mass confusion!!!

Before everybody gets confused:

1- Yes, the headset uses a regular VGA signal
2- Yes, you can get a picture on the headset if you feed a composite sync and a regular VGA RGB signal to each of the headset LCD panels.

What this schematic does is EXACTLY what the controller card does:

-Input a regular VGA video signal
-Convert Horizontal and Vertical Sync into a Composite sync
-Separate the odd scan lines to one LCD panel and the even scan lines to the other LCD panel

The only difference here is that we are no longer limited to a specific screen size and color depth like we were when the video came in through the VESA feature connector.
Nothing more, nothing less.

[pentium]

Re: VGA scan conversion alternatives

Okay, we will disregard threads 16-20 as they are going to confuse people.

Let's try it again.

You pointed out that the DG541 blocks were missing their power connections.
You then pointed me to pages on the datasheet for the DG541.
Now I am confused.

From what you told me, I will require a +12V connection on the "V" pin and a -5V connection on the "V-" pin.

Correct?

[shadow]

Re: VGA scan conversion alternatives

What you have to keep in mind is that every chip that you are going to use, whether it be your flip flop package or your Exclusive-Or gate package or this DG541 chip package. It needs power. They will not operate without power.

I am not sure what voltage would need to be placed on the V+ terminal or the V- terminal (since I have not looked at the datasheet), however I can tell you that they are required. These are the pins that will be powering the chip and making it work.

Now onto my general query . I noticed in the block diagram that whoever wrote it is using Exclusive-Or gates. I do not understand the purpose of them in Block 1. They seem to be just simple buffers. The Exclusive-Or (XOR) gates in Block 2 are simply inverters. Now if Block 1 is simply acting as a buffer, why would a person like to use XOR gates to do the job. They are more expensive, they are slower and there is no benefit from using it instead of say NAND gates. That is unless I am missing something, which I probably am. However I would still like to know the answer .

Now I also hope that all these chips that you are using come from the same manufacturer and are all in the same series of chips. Otherwise I hope that the chips chosen are compatible with each other. Things can start getting really messy in electronics once you start mixing brands and mixing series of chips. If it possible, avoid doing so. Otherwise you will have a hard time because you need to check whether the voltage generated from one chip is compatible with the next chip that it is connected to. If they are not then you have to scratch your head and find a way to make them compatible. Bah, a nightmare to say the least. Just letting you know just in case this is the case.

[pentium]

Re: VGA scan conversion alternatives

What you have to keep in mind is that every chip that you are going to use, whether it be your flip flop package or your Exclusive-Or gate package or this DG541 chip package. It needs power. They will not operate without power.

I am not sure what voltage would need to be placed on the V+ terminal or the V- terminal (since I have not looked at the datasheet), however I can tell you that they are required. These are the pins that will be powering the chip and making it work.

Now onto my general query . I noticed in the block diagram that whoever wrote it is using Exclusive-Or gates. I do not understand the purpose of them in Block 1. They seem to be just simple buffers. The Exclusive-Or (XOR) gates in Block 2 are simply inverters. Now if Block 1 is simply acting as a buffer, why would a person like to use XOR gates to do the job. They are more expensive, they are slower and there is no benefit from using it instead of say NAND gates. That is unless I am missing something, which I probably am. However I would still like to know the answer .

Now I also hope that all these chips that you are using come from the same manufacturer and are all in the same series of chips. Otherwise I hope that the chips chosen are compatible with each other. Things can start getting really messy in electronics once you start mixing brands and mixing series of chips. If it possible, avoid doing so. Otherwise you will have a hard time because you need to check whether the voltage generated from one chip is compatible with the next chip that it is connected to. If they are not then you have to scratch your head and find a way to make them compatible. Bah, a nightmare to say the least. Just letting you know just in case this is the case.

The 74LS73 and the 74LS86 are made by Farchild Semiconductor, the DG541 is made by Temic Semiconductors and there should not be any compatibility issues between them.
Also, don't forget this:

So, I have to supply power to ALL of the chips? oh god, this will be fun. At least I have the datasheets for them all.

[Logistics]

Re: VGA scan conversion alternatives

Does it absolutely have to accept Composite Sync?

[pentium]

Re: VGA scan conversion alternatives

Yep.

[Logistics]

Re: VGA scan conversion alternatives

I don't remember hearing about "native resolution" back in the 90's when LCD/TFT started becoming a big deal. Does the headset have a native resolution?

[pentium]

Re: VGA scan conversion alternatives

As in a preferred resolution? It's hard to tell. I assume it was something like 640 x 480 as back then that was still commonly used.
Why are you asking?

[davmax]

Re: VGA scan conversion alternatives

If you wish to use only a +5V supply you can use two small DC-DC converters to supply power to the two DG541. One +12V and one +5V (output reverse connected to give -5V). Data sheet link is here:

http://www.cdiweb.com/datasheets/meanwell/srs-spec.pdf

SRS 0505 and SRS 0512

Joined Yahoo group today, awaiting approval!

[shadow]

Re: VGA scan conversion alternatives

Your Exclusive-Or package and your JK Flip Flop package require 5V to operate. You need to have +5V on VCC and have ground (aka 0V) connected to GND. The tolerances are fairly tight (to me at least ). It will not work correctly if the voltage is less than 4.75V or above 5.25V.

I checked the datasheets and all the chips seem to be compatible. They have equal voltage values for the appropriate logic levels. This makes life a bit easier.

The DG541 is a tricky beast since I do not understand how the V+ and V- are related yet. However they are very flexible, they are designed to be able to use all sorts of voltages depending what you have on hand and what kind of signal you would like to switch. You really need to find out what sort of voltages you are dealing with the RGB signal. All I know at the moment is that the RGB signal is analog. Therefore most likely you will need to apply a negative voltage at the V- terminal and you probably can not get away with connecting V- to ground (0V).

[pentium]

Re: VGA scan conversion alternatives

Well in that case we should be comfortable with drawing power directly from the PSU since it will supply reasonably stable voltages and, if necessary, supply us with a -5V line. That's easy to do.

Do you want me to modify the schematics so all power now comes in through another connector?

[davmax]

Re: VGA scan conversion alternatives

Well in that case we should be comfortable with drawing power directly from the PSU since it will supply reasonably stable voltages and, if necessary, supply us with a -5V line. That's easy to do.

Do you want me to modify the schematics so all power now comes in through another connector?

Do not follow your statements.

Are you now going to use the +12v and -5V from PSU to supply DG541?

You can modify your connection diagram if you wish. Do not fully understand the question.

[pentium]

Re: VGA scan conversion alternatives

Do not follow your statements.

Are you now going to use the +12v and -5V from PSU to supply DG541?

You can modify your connection diagram if you wish. Do not fully understand the question.

I was just pointing out that if we needed all these other voltages (I did not say we were going to use them) we can just make things easier by leaving the 5V lead I tapped into alone and just draw directly from the PSU in the computer (so we don't have to get all these different voltages from that one 5V line).


Clearer?

[davmax]

Re: VGA scan conversion alternatives

Clearer. You made no comment about DC to DC converters, I presume that possibility is not a goer.

Maybe it is time to take a check on progress.

1. We are taking the input that the RGB levels do not need changing. Just switch them via DG541.
2. DG541 requires +12V and -5V supplies. This will cover the RGB signal without doubt. It is a given that the 74LS86 has +5V supply.
3. A synch converter is being used to drive the fourth switch in the DG541. The output of this switch goes from +5V to zero. If the switch is pulsed with a positive input the output to VFX1 synch is a negative going pulse to ground.
4. The Synch converter in your diagram is the first of two designed by Tomi Engdahl and delivers 1Vpp. This is insufficient drive for the DG541, the converter needs to be simplified to the TTL design (No.2). Remove the transistors and change the pin 13 connection of 74LS86.

I have yet to confirm that the VFX1 does indeed need a negative going pulse from +5V.

[pentium]

Re: VGA scan conversion alternatives

I redrew Fig. 1 to the TTL design however I didn't understand what you meant by changing the pin 13 connections. I also hooked up pin 7 to ground and pin 14 to +5V

[davmax]

Re: VGA scan conversion alternatives

I redrew Fig. 1 to the TTL design however I didn't understand what you meant by changing the pin 13 connections. I also hooked up pin 7 to ground and pin 14 to +5V

the first circuit shows pin 13 connected to ground. The TTL circuit shows it connected to +5V.

I found it interesting that the DG541 switches used for C synch are in fact signal inverters. So far I have assumed that the C synch out of the quoted modules is the same polarity as the signal from the synch converter circuits.

[pentium]

Re: VGA scan conversion alternatives

Oh, I see how I got you confused!
Silly me didn't notice the little numbers meant the pins on the chip and I just hooked it up another way.

[davmax]

Re: VGA scan conversion alternatives

I assumed you were using the same pin connections as per design. Have traced out your connections, you have it correct. Pin 13 original becomes pin 10 in your connection and it is connected to +5V.

[pentium]

Re: VGA scan conversion alternatives

So does fig. 1 look okay?