Still new to the whole composite video thing---could you clarify what is
the stretch? Do you think the driving electronics might not work at the
lower NTSC frequency? Or is there a mechanical impediment, like the
windings of the CRT's yoke? Thank you!
Jens
On 2021-04-11 7:19 p.m., Adrian Godwin 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] <mailto:[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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