Sinclair +2 to VGA without VGA box
A few days ago someone in a Spanish forum mentioned that his friend claimed to have built a cable to connect his Sinclair +2 to a VGA monitor without a VGA box. The only info I was able to get was that he used this kind of cable:
Amstrad Sinclair RGB 15Khz>
LM1881
> 30Khz VGA.
http://www.national.com/mpf/LM/LM1881.html
Would something like this work? If it does, it's much more affordable than one of those VGA boxes. And the idea of having the Speccy connected directly to the PC monitor has a nice ring to it! Add a Belking switch and you can switch between the Speccy and the PC!
edit:
It seems the Atari people have found a way to connect their computers to LCD monitors, if certain conditions are met:
http://www.atari-forum.com/viewtopic.php?t=1516
http://www.atari-forum.com/wiki/index.php/Atari_ST_to_VGA_adaptor
But with no colour, I'm afraid. :/
Amstrad Sinclair RGB 15Khz>
LM1881
> 30Khz VGA.
http://www.national.com/mpf/LM/LM1881.html
Would something like this work? If it does, it's much more affordable than one of those VGA boxes. And the idea of having the Speccy connected directly to the PC monitor has a nice ring to it! Add a Belking switch and you can switch between the Speccy and the PC!
edit:
It seems the Atari people have found a way to connect their computers to LCD monitors, if certain conditions are met:
http://www.atari-forum.com/viewtopic.php?t=1516
http://www.atari-forum.com/wiki/index.php/Atari_ST_to_VGA_adaptor
But with no colour, I'm afraid. :/
Post edited by zxbruno on
Comments
No. The LM1881 can only separate H and V syncro signals from an conposite one. Is still 15 Khz frequency. This only work if the VGA monitor can down to 15 Khz and only a few can do that
Still, it seems the Atari people connect their computer to any monitor (doesn't matter if it supports 15Khz or not), but in monochrome:
http://www.atari-forum.com/wiki/index.php/Atari_ST_to_VGA_adaptor
The adapter mentioned on that Wiki-link, is just an adapter from one type of plug onto another plug. It still requires the Atari to give a 30 kHz signal to use a VGA-monitor.
You could try to get hold of an old Amiga (Microvitec) 1438 monitor, which accepts 15 - 30 kHz signals. But you still only have 15 kHz signal, with the original resolution) available from the +2, so you could really just use a tv.
Yes, but VGA boxes only operate with composite (PAL/NTSC) input signals.
You (probally) get better picture quality using ZX_Spectrum RGB outputs and a small TV set...
There were made scandoublers for Amiga's about 10 years ago. These used the Amiga's 15 kHz RGB-signal and converted it into VGA. A such box, and an adapter, would probably do the trick.
But this box http://www.cypress.com.tw/product.php?PId=90518&CId=001&CName=PC%20Multimedia/Scan%20Converters&SR=1 is probably the thing you're looking for.
(a 625 line to 32 line standards converter, and a 32 line to VGA box. so a 625 to VGA seems feasible with a modern PIC)
I think those scandoublers are custom-built to Amiga hardware, connected directly to "Denise" chip (A500,A2000)
I program myself PIC micro-controlers and i don't see a PIC doing video standards conversion...Maybe an DSP with fast ADC/DAC converters...
But a PIC can generate a VGA output, like a TV game or monitor patterns generator.
obviously there were other components in there! fast ADCs and such, but the PIC was the main processing part
I the "later days" of the Amiga's, there were also external scandoublers that were connected to the 23-pin video outlet. I can't remember exact dates, but they came after the A1200 was released. Don't remember who made them either, but is sure wasn't C=.
:lol:
I won't buy a multi-system tv. I won't, I won't, I won't. :grin:
The PAL TV card will do for now. It has TV and composite video input. I can use it with any Spectrum. I want to have the LCD monitor, the Spectrum on top of the computer table in front of the LCD monitor, and the PC keyboard on top of the keyboard drawer. Perfect set-up. :)
I almost bought Sintech's VGA box for CRTs, but since I got one 17" LCD for less than 30GBP, I got rid of the CRT. :)
Yes, the PIC is "controling all the thing" :smile: , surelly using TV color decoder
chips, the PIC is controling them using i2c bus protocol.
Yes. But they are Amiga specific. There are lots of external signals present
in the 23p outlet. One LM1881, two "inverter" buffers for H/V sync signals, +5V (and maybe +12V) power supply. This maybe work ! ;)
Gods, you seem to know at least something about scan doublers (at least you do PICS!). I do not.
Can you tell me if a scandoubler just multiplies the Sync Frequencies (15625 Hz / 50 Hz, I think), or does it also fiddle around with the video signal? :confused:
I'm assuming it has to fiddle with the video, otherwise one would end up seeing either half or two images side-by-side, huh? :o
If it does not have to, I think an LM1881 and a PLL frequency doubler would do the trick, but I think that's an incredibly cheap & easy solution someone would have come by with already... :grin:
Thanks,
Marcelo.
No, it scandouble and deinterlace PAL RGB input. It work by "doubling" each video lines. To do this job it need some SRAM chip to store the line to be displayed at this time. You have one simple scandoubler (for C128 ) at:
http://starbase.globalpc.net/~vanessa/hobbies/projects/scandoubler-schematic-0.2.3.png
Hehehe... Yup, my idea was too "bright" to be viable! D'oh! :oops:
Thanks for the link! The schematic will go straight to the "someday I'll do it" room (a drawer was simply not enough) :lol:.
Marcelo.
This schematic is "too simple", it never work with ZX_Spectrums. It was build for commodore C128 computers. The C128 graphical chip is also "synchronized" by the scandoubler.
No, C128 have TTL (0-5V) RGB output. ZX_Spectrum is analogue output (0.7V at 75 Ohm). ZX_spectrum +2 have 3x 150 Ohms in RGB lines to do this conversion. But if you discard thoses resistors (with a junper), eliminate the 3x 1N4148 diodes in "Bright" line and transform this line in one "intensity" (TTL) output...You have TTL RGB outputs ! :wink:
(For the scandoubler, i may have take the wrong example...)