On 26/11/2022 07:11, olaf wrote:
> Jerry Xu <jer...@sdf.org
> >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
> 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.
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
- 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
- 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
- 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.