Oh, yes, the entire discussion is about monochrome video. Sorry, should
have mentioned it in the follow up email as well.
On 2021-04-11 9:26 p.m., gregebert wrote:
At least it's just monochrome. NTSC composite video with color is
rather complex, though I must say it is also ingenious in that it is
backward-compatible to monochrome and packs so much video information
into a 3.58Mhz bandwidth. Similar for PAL, though higher bandwidth.
On Sunday, April 11, 2021 at 4:19:20 PM UTC-7 [email protected]
wrote:
It sounds a bit of a stretch - 15kHz to 19kHz. You could try
running the monitor without an input signal and adjusting
horizontal frequency (if there is one) to see what range it can
manage.
Another possibility is to fix it in software by creating a custom
monitor signal. Some information is at
https://github.com/raspberrypi/documentation/blob/master/configuration/config-txt/video.md
<https://github.com/raspberrypi/documentation/blob/master/configuration/config-txt/video.md>
On Sun, Apr 11, 2021 at 10:51 PM jb-electronics
<[email protected]> wrote:
Thank you! I think it should be possible to modify the
horizontal and vertical deflection circuitry on the board to
make it a proper NTSC frequency, yes?
Jens
On 2021-04-10 10:52 p.m., 5-ht wrote:
Jens,
The horizontal sync requirement of this monitor (52 uS /
19.2Khz) is somewhat higher than a standard NTSC signal which
is about 63 uS / 15.7 Khz.
Mark
On Saturday, April 10, 2021 at 8:04:15 AM UTC-5 Jens Boos wrote:
Thank you! I did some more digging and found the service
manual for the display (Panasonic TR-60S1A, see here:
https://www.opweb.de/english/company/Panasonic/TR-60S1A
<https://www.opweb.de/english/company/Panasonic/TR-60S1A>)
There is is a timing chart (see below). It looks an awful
lot alike NTSC to me, can somebody confirm?
Best wishes
Jens
On 2021-04-10 12:28 a.m., Adrian Godwin wrote:
It's easy enough to extract the sync signals, as you've
seen. It may not be particularly difficult to modify the
TTL input to analog, or to create a TTL level signal if
you don't need a grey-scale. On many general-purpose
monitors like that they could often be built for either
standard - the microvitec Cub popular with the BBC
Microcomputer had that option.
But the critical thing is that it runs at the right
speed. CRT circuits are built around the line oscillator
which generates the horizontal scan AND the EHT voltage.
It was only when multisync monitors came along that the
optimisation was split to reduce the dependency. And if
the frame frequency is wrong, you will often have
problems getting a full frame scan when you force it
into sync.
So the first thing is that you need to make sure the
8920 monitor ran at either PAL or NTSC rates so you can
choose a raspberry pi format to match. There's a good
chance it's NTSC but later monitors like the ones in the
54 series of digital scopes were more like the IBM
standards MDA and EGA (CGA was NTSC).
On Sat, Apr 10, 2021 at 4:28 AM jb-electronics
<[email protected]> wrote:
Hi all,
This is a bit of an off-topic question, but I hope
there will be
somebody here that can help. I have bought a new-old
stock monochrome
CRT for a HP Agilent 8920A, basically this unit here:
https://www.ebay.com/itm/273930914548
<https://www.ebay.com/itm/273930914548> .
It looks to me that it is just a rebranded
OmniVision 6" display:
http://www.omnivisionusa.com/Industrial-LCD-CRT-Monitors/replacement-crt/crt-monitors/6-inch-kit-.html
<http://www.omnivisionusa.com/Industrial-LCD-CRT-Monitors/replacement-crt/crt-monitors/6-inch-kit-.html>
Now unfortunately it takes TTL video as input. But I
have a composite
source (a Raspberry Pi). How can I convert composite
into TTL? I
basically need to extract Hsync and Vsync and feed
it separately to the
unit, okay. There is an old circuit here that does
just that:
https://www.elektormagazine.com/magazine/elektor-198812/47485
<https://www.elektormagazine.com/magazine/elektor-198812/47485>
But I know there are also dedicated chips, like the
GS1881:
https://www.mouser.com/datasheet/2/761/GS1881_GS4881_GS4981_Datasheet-769183.pdf
<https://www.mouser.com/datasheet/2/761/GS1881_GS4881_GS4981_Datasheet-769183.pdf>
So basically here is my question: before I dive into
this any further,
is there any chance of success? What is the optimal
choice? Or is it
quite unlikely that I will be able to convert the
signals? I mean, even
if I manage to extract Hsync and Vsync, is it likely
to work?
I am sorry for the naive question, but I am no
expert on video signals,
and it would be nice if anybody more experienced
could chime in with a
few words of caution/experience.
Best wishes
Jens
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