LCD Screen Output (HP-49, 110+)

[Martin Hepperle]

Hello,

some members of the HP-38/48/49 family and the Portable Plus come with an LCD output connector. The connector carries a pixel clock signal and several data lines for parts of the display (display memory is often split into 2 (HP-49) or 4 (Portable Plus) parts).

I know that there was an overhead panel e.g. for the HP-49 available.

Has someone ever made an interface to display the screen content via these LCD interfaces on an external screen?

Nowadays we have high contrast LCD or even color TFT screens and it should be possible to create a secondary display of high quality and readability.
Due to the high pixel clock rate one would probably have to create an FPGA hardware solution, a cheap microprocessor solution (Arduino, Raspberry) will be too slow. Output could be a composite video signal or something like HDMI.

Would this be feasible?

Martin

[Dave Frederickson]

(12-05-2014 02:25 PM)Martin Hepperle Wrote:  Has someone ever made an interface to display the screen content via these LCD interfaces on an external screen?

Yes. The 82985A Monitor Interface for the Portable PLUS.

[Martin Hepperle]

(12-05-2014 02:31 PM)Dave Frederickson Wrote:  

(12-05-2014 02:25 PM)Martin Hepperle Wrote:  Has someone ever made an interface to display the screen content via these LCD interfaces on an external screen?

Yes. The 82985A Monitor Interface for the Portable PLUS.

... darn, I did not see this. However, I have some slight difficulties to order one and for $425 it seems to be a bit High-Priced ... but I will have a look at the schematic.

Martin

[Dave Frederickson]

(12-05-2014 04:44 PM)Martin Hepperle Wrote:  

(12-05-2014 02:31 PM)Dave Frederickson Wrote:  Yes. The 82985A Monitor Interface for the Portable PLUS.

However, I have some slight difficulties to order one and for $425 it seems to be a bit High-Priced ...

$425 is not the selling price, but the original price in 1985. The link is to the HP Computer Museum, not a store.

[BruceH]

(12-05-2014 02:25 PM)Martin Hepperle Wrote:  Due to the high pixel clock rate one would probably have to create an FPGA hardware solution, a cheap microprocessor solution (Arduino, Raspberry) will be too slow.

It doesn't have to be any faster than the screen refresh rate of the built-in LCD - which isn't the fastest thing in the world, for the 39/49 at least. An RPi would do the job.

[Martin Hepperle]

(12-05-2014 09:51 PM)Dave Frederickson Wrote:  

(12-05-2014 04:44 PM)Martin Hepperle Wrote:  However, I have some slight difficulties to order one and for $425 it seems to be a bit High-Priced ...

$425 is not the selling price, but the original price in 1985. The link is to the HP Computer Museum, not a store.

Dave,

I am well aware of that - I was just trying to be funny ... and obviously failed...

Martin

[Martin Hepperle]

(12-05-2014 11:22 PM)BruceH Wrote:  It doesn't have to be any faster than the screen refresh rate of the built-in LCD - which isn't the fastest thing in the world, for the 39/49 at least. An RPi would do the job.

That's how I understand how the system works:
The screen refresh rate is about 50Hz, but the pixels are sent out as several serial streams - one for each quadrant of the screen (Portable: dot clock <= 1.25 MHz). They would have to be captured, combined and stored in a RAM and then, after a frame is complete, one would have to output the frame according to the external display needs, e.g. scan line by scan line. Therefore I think one has to capture the data at a relatively high rate.
In case of the HP-49G the screen is split into two halves, so that only two pixel streams have to be captured. It would be a nice project to hook up modern TFT screens to these machines.

Martin

[Dave Frederickson]

(12-08-2014 10:26 AM)Martin Hepperle Wrote:  

(12-05-2014 09:51 PM)Dave Frederickson Wrote:  $425 is not the selling price, but the original price in 1985. The link is to the HP Computer Museum, not a store.

Dave,

I am well aware of that - I was just trying to be funny ... and obviously failed...

Martin

Hi Martin,

Sometimes I have difficulty detecting humor in forum posts. Perhaps you could help me out and add a smile to you humorous posts.

I agree, $425 in 1985 is over $900 in 2014! I have the Portable PLUS part so if you come across the 82985A please let me know. Here're a couple of pics of the connector panel for the Portable PLUS. That's my prototype in the bottom two pics.

Dave