Using an old Casio calculator's display

[fridgecow]

I have a calculator very similar to this one (same chip/screen) and would like to reuse the screen with my Pi. The display has a large ribbon connector, and some experimentation shows that each pin corresponds to a row/column. How would I a) connect this to the pi and b) output to it?

[DougieLawson]

Time to formulate plan B.

The chances of being able to connect some random display from any old kit are so close to zero that it is pointless.

Plan B is simple: buy a supported HDMI, RCA analog a/v, USB or SPI display and use that.

[Burngate]

With enough information, it might be possible, though unlikely to be worthwhile.

Having ascertained that the screen is addressed as a matrix, you'll need to find out what voltages are both required and safe (it would be irritating to almost complete the project, only to find it died on you)

If it really is a matrix, it should be possible to drive it in a similar fashion to the many LED matrices around - it appears to have about 32 rows, and maybe 64 or 96 columns?
Obviously, the Pi hasn't that many GPIO pins, so maybe I2C expanders could help there. Since the image will be static, they should be fast enough?

Driving an LCD isn't as straight-forward as applying a voltage - that may be ok for testing, but can age the display quite rapidly. They're generally driven with a square-wave, with the other electrode driven in anti-phase (though there are many variations on that theme) You may have to find out what it's expecting, before designing the electronics.

As DougieLawson has said, Plan B is optimum, though Plan A might be worthwhile if you have a spare year or so, lots of money, and an obstinate streak.

[toxibunny]

Try a bunch of shift registers in order to multiply your gpio pins. those lcd displays work with very low voltages too, so be aware. fractions of a volt should do it, or maybe even less - google it. resistors will no doubt be vital here.

imho, the biggest challenge will be physically putting an adaptor board together. hopefully you've got a socket for that ribbon cable. if not, then the low power requirements will allow you to bodge something up with thin wire, conductive glue, and a steady hand.

If it really is a matrix, then it really shouldn't be all that difficult. definitely make sure you don't do anything daft like putting 5v into it and burning it out though. good luck!

[DougieLawson]

Getting a hd44780 based LCD matrix running with the RPi is going to be more successful more quickly.

[fridgecow]

Ahhh okay everyone. I just thought it would be 'fun', and possibly save a tiny bit of money, but I'm seeing now I was mistaken. Thank you for the help, seems my old calculator has died in vain!

[toxibunny]

Sounds like fun to me.

btw, hd44780-controlled lcd displays are easy to get working, and are relatively cheap, but you don't get pixel-level control...