HP-48GX cards other than RM/ROM?

[Jeff_Birt]

I dug out my HP-48s to play with and got to wondering if there were every any other types of expansion cards made for the GX other than RAM/ROM. The Port 2 connector has some signals related to the LCD and I watched a video at lunch today of HHC 2018 that talked about the 50G LCD projector connector which insinuated that the 'something' might be done with these signals on the 48.

After spending some time searching the interwebs I have not found any such device or project. Perhaps the physical constraints of creating such a card made using the relatively simple, and external, serial port connection a more attractive option.

[Eric Rechlin]

The InVision 48 projector panel plugged into the card slot of the 48SX/48GX and then was placed on top of an overhead projector to project the calculator's display. For the 38G/49G model of the product it used a cable into the oversized serial port on those models, but originally it only worked through the card slot.

[Jeff_Birt]

Thanks Eric. I could not find the correct search terms to track down the projector interface but after you provided the name it was quite easy. Knowing the search terms in the key

https://literature.hpcalc.org/community/...ohd-en.pdf

[Eric Rechlin]

There was also a similar product direct from HP, I think just called the "HP Overhead Display", part F1212A, but I haven't come across documentation for it.

[brouhaha]

(10-27-2023 07:25 PM)Jeff_Birt Wrote:  I dug out my HP-48s to play with and got to wondering if there were every any other types of expansion cards made for the GX other than RAM/ROM. The Port 2 connector has some signals related to the LCD and I watched a video at lunch today of HHC 2018 that talked about the 50G LCD projector connector which insinuated that the 'something' might be done with these signals on the 48.

After spending some time searching the interwebs I have not found any such device or project. Perhaps the physical constraints of creating such a card made using the relatively simple, and external, serial port connection a more attractive option.

Bizarrely, HP did not provide a vertical (frame) sync signal. There was a kludge to detect frame sync by the state of a bit in a scan line outside the visible area, but that was not rntirely reliable, so the displays that were sold also had buttons for manually adjusting the vertical sync.