HP 82985A video interface for the Portable Plus - poor image quality

[Martin Hepperle]

(08-16-2022 07:21 AM)Klaus Overhage Wrote:  This picture shows my old 19 inch Belina VGA monitor connected to an Extron DVS 304. I read about it in the thread HP-75C Demo and can confirm it produces a very clear, steady image.

I also have this interface and am very happy with it. I am using it with a small TFT panel and the picture is much, much better than the built-in LCD screen. Especially if you compare with the early gray LCD. But also compared with the green LCD variant it is much better.
There are some glitches (uneven character stem widths) due to scaling/aliasing to the TFT resolution, but this is expected.
The inverse video parts indeed "bleed" a bit, but if you really work with the Portable, you will not do much in PAM.
I have written a few Turbo Pascal programs using this video interface and find it very useable.
If you use the NEC/HP green monitor, you might want to reduce brightness, this might also help to obtain a better image with less bleeding.

It might be an interesting project to build a new interface for this purpose but one has to sample the digital LCD output at a relatively high rate so that one would probably have to revert to a FPGA or similar device. Such a new interface could be designed to better match the resolution of modern TFT screens and avoid generating analog output.

Martin