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 . > > 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 > > 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 > > But I know there are also dedicated chips, like the GS1881: > > 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 > > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/e0f398e8-24b1-952c-c998-0ddfbed6849e%40jb-electronics.de > . > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/CALiMYrvHCiXd3QSDmEJ%2Bpe3XgUutOC_C3yLFGxeOEo2bjtEAWw%40mail.gmail.com.
