Composite or VGA output through edge connector

[spawnerbr]

Hi all. There is a simple way to take from the edge connector a composite or VGA output from ZX81? Maybe a simple interface, not like Chroma 81. Is just because I have some ZX81 clones that the video output from RF is horrible and the only way is have very old TVs to use them, so I'm looking for a easy to have video output not opening the computers. There is something like that? Thanks

[mrtinb]

The only way for video output on edge connector is the Chroma interface. It is quite complex to create a picture from the edge connector, as there is no video output there. The Chroma interface is complex, because it remembers all the events on the address and data bus, and builds a picture from all information and recreates, what it believes is on the tv.

If you want VGA output I only know of the ZX-Wespi-V. This is not a ready made interface, but a recipe how to connect it inside your ZX81. 2 wires need to be soldered to your ZX81's PCB, and the power/ground can be taken from the power jack. You need to upload the firmware to an ESP32 board as well.

https://github.com/holmatic/zx-iot-video

[spawnerbr]

The only way for video output on edge connector is the Chroma interface. It is quite complex to create a picture from the edge connector, as there is no video output there. The Chroma interface is complex, because it remembers all the events on the address and data bus, and builds a picture from all information and recreates, what it believes is on the tv.

If you want VGA output I only know of the ZX-Wespi-V. This is not a ready made interface, but a recipe how to connect it inside your ZX81. 2 wires need to be soldered to your ZX81's PCB, and the power/ground can be taken from the power jack. You need to upload the firmware to an ESP32 board as well.

https://github.com/holmatic/zx-iot-video

Thanks for reply. What I'm looking for is a way to have video with good quality like composite or VGA but not opening the computer. I have some composite boards that I use sometimes to test my ZX81 clones, but wanna practicality on this Chroma 81 is the best way, just need a new batch. Thanks!

[mrtinb]

There are only two options:

• Chroma interface without modification
• Composite modification or Wespi modification

[bola_dor]

To get video out the border connector you have to build it from scratch replicating the ULA work outside. That's what the chroma interface or de ZX-HD does (this late for the spectrum).
Just being curious... what clones do you refer to? I have several myself some of them (without a ferranti ULA) doesn't produce a backporch signal. Some times you need an old TV set, others you até luxky and a new LCD one just do the job.. I have one 60" LCD that some times needs me to make a blind SAVE and then break to get in Sync at first start with some machines...

[1024MAK]

As Martin says, there is no video signal available on the expansion port / edge connector on a ZX80, ZX81, TS1000 or other official ’clone’ that uses the same pin-out.

The Chroma interface cheats. It records memory writes to RAM by the Z80 CPU in it’s own RAM. Then uses it’s own custom logic to replicate the video functions of the ULA and in so doing, creates it’s own video signal.

The only inexpensive way to get a composite video signal from a ZX81, TS1000 or other official ’clone’, is to open the case and carry out a modification.

Mark