Harlequin video modifications

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PokeMon
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Re: Harlequin video modifications

Post by PokeMon »

Yes - I can use composite video and RGB at the same time.
I can connect both signals to my broadcast monitor, it's a high quality SONY BVM9045D.
I can switch between composite and RGB simply by clicking on the front and that was the reason to have the same output level or brightness when switching. The monitor was calibrated a few weeks ago by a professional video company where I bought it from.

So I measured the voltage levels and they match exactly what you can calculate from resistor values. The maximum (bright) color value is 2.0V at the base of the transistors and about 1.3V at the emitter. So the resistors R19,R20,R21,R34,R38,R43 will give nearly 700mV (calculated 682mV) when choosing these resistors as 68R in combination with the 75R input impedance. And - more important - the output level of RGB and composite video is identictal.

The relationship of bright and non-bright colors are okay and not touched through this mod (75% of full range signal with bright set).
superfo
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Re: Harlequin video modifications

Post by superfo »

PokeMon wrote:I can connect both signals to my broadcast monitor, it's a high quality SONY BVM9045D.
I can switch between composite and RGB simply by clicking on the front and that was the reason to have the same output level or brightness when switching. The monitor was calibrated a few weeks ago by a professional video company where I bought it from.
As I understand your monitor can accept both composite and RGB, I am not sure when you switch between input, the internal 75 ohm still connect to both inputs or not.
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PokeMon
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Re: Harlequin video modifications

Post by PokeMon »

Well thats not really important. In fact I don't understand your question. Both outputs are completely different by different drivers or buffers. Composite is buffered through AD724 and the RGB are buffered through the transistors Q2,Q3,Q4. As these are emitter followers, the output level at the emitter is always 1.3V regardless if RGB is connected (and terminated with 75R) or not. There is no interdependency. I could even short the RGB output signals at the mini din connector.
superfo
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Re: Harlequin video modifications

Post by superfo »

I understand your point, I ask McLeod if he have any comment.
I'm OK to change the value of resistors, a group of forum's members in Spain is going to order the new batch.
Maybe they want to know a bout this change.
Jose_Leandro
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Joined: Fri Nov 25, 2011 3:58 pm

Re: Harlequin video modifications

Post by Jose_Leandro »

Hi

My name is José Leandro and I helped superfo with the develop of the first versions ( a-e) of the Harlequin clone.

First:
I would to say sorry because English isn't my first language and I don't have enough level to have a fluent convertation
Also because I'm direct person and not very polite. I am not attacking you with my opinions.

your question

Why not s-video?. Easy, I'm not interested in this solution. I toke a look to all my tv ( and also girdfriend's tv). All of them have composite video and scart connector (rgb). All CRT tv and Small ( and cheap) lcd TV don't have s-video. Only big LCD have.

- When I go to a retro party, most people go with crt and little lcd. Most of themhad the same configuration ( rgb and/or composite)
- Easy solution
- S-video mod are more common outside europe ( when RGB connector are more rare).

Like Harlequin is a native RBG machine, the composite option was nice for my. But if you like s-video , the ad724 option was a good desing decision because it easy to do.

Why minidin connector? I like superfo solution for rgb connector. Harlequin clone was desing to fit in a spectrum / spectrum + case. The minidin allow not cut spectrum case. Other connector? well, standard DIM ( like spectrum+128k,spectrum +2,+3, amstrad cpc, dragon 32, etc, etc) won't fit in spectrum case.

I read you propose a connector with 9 pins. I suppose you are talking about sub-d 9 pins. It's bigger connector and I don't think it'll fit without modifications in a spectrum case. I thinl it'll be a worst solution that superfo toke with minidin.

RGB signal. Well, I remembered that we have some problem with this part. Rev-a has also strange problemw when you try to connect two tv ( one with composite and other with rgb). The bright change a lot.

When you say that you take a look with the scope to rbg signal. Did you make it with or without tv? I say that because you are wrong in one thing. The TV imperance affect to rgb signal (and also to ad724 at least in rev a-e ).

Like superfo say, in this point we ask for help to McLeod / Chris order to improve rgb signal ( and also for NTSC mode) without lossing the zx spectrum palette. You can read the discussion desing int the document that Superfo has put.

The solution we toke maybe it was not the perfect solution but it worked in most of case. I say that because my experence say that you modification will be OK for you harlequin and your monitor / tv but not for other people. One TV model can work a bit diferent that other ( if it happen with original spectrum , why not with Harlequin?)

Thinkin about it, pobably it was my fault my decision of choise this configuration and not take a configuration like spectrum +3. RGB signal more high and the necessity of make a rgb cable with resistor. With this configuration, you will assume taht you have to put a cable with resistor acording to your requirement.

Bye

José Leandro
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PokeMon
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Re: Harlequin video modifications

Post by PokeMon »

Hi José,

thanks for your participation.
Well, design decisions are mostly influenced from personal preferences.

Referring the S-Video connection, this is more and more popular as the video quality is significantly better than the composite mixed signal. Nearly all better TVs or monitors offer this connection at front side to connect a video camera easily. So nearly any TV I would buy (I am not talking about the china garbage) has this connection. In the same way SCART is getting less popular over years as this is a very old connector type and many TVs offer these for compatibility reasons to old hardware only. You have usually more HDMI and USB connectors than SCART. The access of SCART is also problematically as this is offered at the backside of TVs only - to bad when already mounted at a wall.

About the influence of RGB connected monitor to composite signal - yes you are right there is a little bit influence but not as much as worth discussing. When shortening all RGBs (I did it for test purposes over the internal 68R resistors) I can measure about 40mV decreasing RGB output level and in the same way see a small difference when connecting the short jumper or let it open. When I use 75R termination resistors this effect is reduced to about 20mV. This can be seen on display when switching but I would say you can not say if the pins are terminated or not when just seeing the picture brightness, only in direct comparison. Anyway - here we are talking about 3% of full range level.

Test with short outputs:
RGB_shortk.jpg
RGB_shortk.jpg (167.76 KiB) Viewed 10834 times
Test with 75R termination:
RGB_75Rk.jpg
RGB_75Rk.jpg (155.34 KiB) Viewed 10834 times
Jose_Leandro wrote:The solution we toke maybe it was not the perfect solution but it worked in most of case. I say that because my experence say that you modification will be OK for you harlequin and your monitor / tv but not for other people. One TV model can work a bit diferent that other ( if it happen with original spectrum , why not with Harlequin?)
In that point I disagree. There is a norm for video signals defining levels very properly and this should be respected. It is fact that not every display delivers same good picture quality, strength, sharpeness, colour intensity - but it is wrong to compensate a poor picture quality by modding the video levels. The approach is to have a Harlequin with a standard output signal. What if you go to your next LAN party and connect it to a high quality monitor ? Would you change the resistors ? Should everybody match the signal in a personal way to best fit his home equipment ? I don't think so.

Here is a good summary of video levels of different signals and TV norms.
http://www.maximintegrated.com/en/app-n ... vp/id/1184
shadow338
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Re: Harlequin video modifications

Post by shadow338 »

Hello all,

I know that this thread is been quiet old but I would like to ask a few questions.

1 - Pokemon says: "The Harlequin uses the AD724R circuit to create a composite video signal and I wonder why the signals Chroma und Luma are not used as it offers a S-Video (Y/C video) output for free which give a better color signal than the composite video. "

Q: Does this means that the 8 pin connector on the harlequin is not able to provide S-video quality video? What's the role of the 8 pin connector then and what it does exactly?

2 - Ok so the harlequin uses a 8 pin connector. No big deal. The thing is, all lcd's that I came across (including mine) have 4 pin input connectors.
Q: It is possible to convert 8 pin to 4 pin without loosing video quality? (I assume there is a cable/converter out there that does this).

3 - This one may be a silly question:
Q: I know that I can convert s-video to an RCA cable, but does this means the signal will be converted to composite or can convert s-video to an RCA and keep the s-video quality?


Thank you!
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1024MAK
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Re: Harlequin video modifications

Post by 1024MAK »

The 8 pin mini DIN connector is for the RGB video output signals.

There is NO S-video output on this connector.

The RGB (and sync and audio) signals on the 8 pin mini DIN connector are used to feed to a RGB SCART equipped television.

For a proper conversation of S-Video to composite video, you really need a properly designed mixer circuit. But some people in the past have bodged various simple circuits using resistors and capacitors and reported that it "worked for them", but it does not work for everyone.

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PokeMon
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Re: Harlequin video modifications

Post by PokeMon »

1024MAK wrote: There is NO S-video output on this connector.
Yes but it is available at the chip and can be wired to this 8-pin mini din connector.
In the first postings I described exactly how I did this.
On my connector I have now both, RGB and S-Video and I use of course own cables.
Anyway there is no standard cable existing for connecting monitors/tv's via this socket, as far as I know some guy in spain made the cables with Scart connector more or less by "hand". ;)
shadow338
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Re: Harlequin video modifications

Post by shadow338 »

thanks PokeMon, I will probably try one of your mods.

My goal is to move away from s-video in favor to HDMI, so I will try your RGB mode and then use a converter from RGB (component) to HDMI.

Hopefully it will work.
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