HP48 LCD

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olaf

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Jan 28, 2022, 1:15:04 AMJan 28
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I look at this schematic of the HP48SX:

https://www.hpcalc.org/details/3543

It shows that the screendriver-circuit are two SED1181 serial connectet.

I think that is unusual because the datasheet of the SED1181 claims
that it build together with an SED1191 for a matrix-lcd.

I wonder if it is possible to grab the two data-bit in a microcontroller
and translate it for an oled for a much better readable display.
Did knows the code that generate the LCD-Signal to the output bits?

I still like my old HP48, but the low contrast of the early graphic-lcd,
are very poor by todays standard.

Of course it is now only an idea. :-)

Olaf

Jerry Xu

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12:00 AM (13 hours ago) 12:00 AM
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Hi Olaf, I Think your idea is definitely possible. Since the data sheet of
SED1181 is obtainable, we may just use one STM32, or any other kind of
micro-controller, to build an converter.

I just got a set of HP48 with keyboard problem, I may attempt to dissemble
it and go forward to build a converter. It sounds a fun little project to
do.

JX

olaf

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2:15 AM (10 hours ago) 2:15 AM
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Jerry Xu <jer...@sdf.org> wrote:

>Hi Olaf, I Think your idea is definitely possible. Since the data sheet of

I know that it is possible because I connected my Logicanalyzer to the
datastream. :-D

>SED1181 is obtainable, we may just use one STM32, or any other kind of
>micro-controller, to build an converter.

It is not so easy. The HP sends 2x67bits. ARGH! That is a little
bit unusual for traditional SPI Hardware in any controller.
Perhaps with RP2040 or an CPLD/FPGA. But in this case we have
to think a little bit about power consumption. .-)

>I just got a set of HP48 with keyboard problem, I may attempt to dissemble
>it and go forward to build a converter. It sounds a fun little project to
>do.

Strange, I have many HP48 because I bought them wenn they are cheap,
but I have never seen a keyboard problem. Only the HP49 ist famous for
it and I have a 49 with broken Keyboard.

BTW: Ich bought my first HP48SX in 1990 for 700DM, in the first year I
pour out a cup of tea (with sugar) on it. I had to open it without
youtube video (looks strange since this opening), I dryed it, but
never opend the keyboard themself. It is still working! The first
years the keys felt a little bit rough because of the sugar, but the
sugar is pressed to dust and it feels like new in the last 20years. So
I think the keyboard is bulletproof.

Olaf

Bruce Horrocks

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9:07 AM (3 hours ago) 9:07 AM
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On 26/11/2022 07:11, olaf wrote:
> Jerry Xu <jer...@sdf.org> wrote:
>
> >Hi Olaf, I Think your idea is definitely possible. Since the data sheet of
>
> I know that it is possible because I connected my Logicanalyzer to the
> datastream. :-D
>
> >SED1181 is obtainable, we may just use one STM32, or any other kind of
> >micro-controller, to build an converter.
>
> It is not so easy. The HP sends 2x67bits. ARGH! That is a little
> bit unusual for traditional SPI Hardware in any controller.
> Perhaps with RP2040 or an CPLD/FPGA. But in this case we have
> to think a little bit about power consumption. .-)
>
> >I just got a set of HP48 with keyboard problem, I may attempt to dissemble
> >it and go forward to build a converter. It sounds a fun little project to
> >do.
>
> Strange, I have many HP48 because I bought them wenn they are cheap,
> but I have never seen a keyboard problem. Only the HP49 ist famous for
> it and I have a 49 with broken Keyboard.

Hi Olaf,

That 49 might help you with your OLED problem even with a broken keyboard.

I don't know if you are aware but HP produced an overhead projector
display for the 49 for classroom use and used pins 5 - 10 on the 10-pin
connector on the calc to carry the raw LCD signals to the OHP display.

You could try using this to prototype your OLED display adaptor and then
modify it to get signals direct from the 48 once it is working?

The pinouts of that connector are:

Top of Calculator

6 7 8 9 10
+-----------------------+
| o o o o o |
\ o o o o o /
---------------------
1 2 3 4 5

Bottom of Calculator


"Pin" Signal
1 Shield
2 TX
3 RX
4 SGND

5 VCO
6 XSCL
7 LP
8 LD0
9 LD1
10 GND

where:
- LP is line pulse - goes high when a new LCD scan line is about to start
- XSCL is column pulse - goes high as each column is reached
- LD0 & LD1 are the pixel values for the left half and right half of the
display
- VCO and GND I don't quite understand. The data signals are 0-5V with
respect to VCO but 0-9.5V (more or less) with respect to GND. This may
just be something to do with powering the OHP display unit because it
needs a 9V battery when used with the HP48SX card but not when used with
the HP49G.
- lastly there's no 'start of screen' signal as they ran out of pins.
The OHP unit has a microswitch that moves the whole display 'up' one
pixel row each press and you use that to align the top of the display
with the top of the LCD. Most times it starts just fine - it's only if
you plug in while the calc is running that it can get out of sync.

I started on an Arduino project to read the signals and then
(eventually) Bluetooth the display to a PC, got so far and then got
distracted by other projects!

There's some sample output here.
<https://1drv.ms/b/s!AjwWLJj3pb2Qk38dgtjCo54lf-Mf?e=VUHeJE>


--
Bruce Horrocks
Surrey, England

olaf

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9:45 AM (3 hours ago) 9:45 AM
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Bruce Horrocks <07....@scorecrow.com> wrote:

>I don't know if you are aware but HP produced an overhead projector

I know that it existed somewhere. :)

>You could try using this to prototype your OLED display adaptor and then
>modify it to get signals direct from the 48 once it is working?

Na, it is not a problem to solve this problem somehow.

I only have to use some powerful hardware. I think for example
an RP2040 could do this. Or perhaps a smaller Controller
with some dirty tricks. (external Register, small CPLD, Assembler)

But I like to think about a more elegant solution. :-)

However an OLED inside the HP48 needs some reworks for the
battery compartment, too. (goto Lithiumpower)
Anyway it would be nice not the heat up a to powerful
controller for this job.
But I guess I will start with the RP2040 and downsize it later.

>5 VCO
>6 XSCL
>7 LP
>8 LD0
>9 LD1
>10 GND

What you describe is the direct inteface to the old LCD-Driver HP uses
in the 48. :) I soldered it with a busdriver to my HP48, too.
It looks now a little bit frankensteined.

>I started on an Arduino project to read the signals and then
>(eventually) Bluetooth the display to a PC, got so far and then got
>distracted by other projects!

THat is my problem, too. The HP48 is number two in my project
list. Number one is to connect a very special Tektronik probe to my
cheap RTB2004. .-)

Olaf


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