I have come into the possession of a GLCD that I'd like to have a crack at using on my Arduino, but it currently uses an 18-pin connector, which is gonna use up pretty much everything I have available on my little UNO style board.
I already have a 20x4 character LCD which has been converted to use I2C, and I am wondering if I can potentially do the same with this board too. The board has an LC7981 controller, and I think it is probably the 240x128 panel size (my rough calcs came up with 224 x 140, so I am waiting on the manufacturer to confirm this for me, as there are no reference numbers on the board to give this info away). Note - I haven't even powered it up yet, so forgive me if the first thing it will do when I apply power is to give me that information as it boots...
If it is feasible to drive this GLCD via I2C, can you give me some advice on what I need? Are all I2C boards created equal, or do I need one that is specifically geared up for this display (or at least for this controller)?
Thanks
Graham
(PS - if this post should really be in the I2C section of the forum, then please feel free to move it or let me know so that I can repost it there)
The popular I2C adapters for 16x2 displays bit-bang the 16x2 in 4-bit mode.
They are not suitable for your display. You would need to bit-bang the LC7981 in 8-bit mode which needs a bigger chip than the PCF8574. And you would need to make it yourself.
The alternative is to use an intelligent microcontroller. It appears as an I2C Slave and controls all the LC7981 pins. You could use a Tiny2313 or PIC. Or any MCU with enough pins and hardware I2C capability.
As far as I know, no-one has written an Arduino library for a PCF8575 (the 16-bit version of PCF8574)
And no one has made an 8-bit Tiny2313 backpack.
So it would require a LOT of effort on your part. Much easier to buy a ST7920 display which has an SPI interface and existing libraries.
Yes, it would be an interesting project if you had a shed full of thousands of these displays for sale.
You would need to design, build and assemble a custom backpack.
Even so, it would be hard to compete with Chinese ST7920 modules.
David.
Regarding an intelligent MCU adapter. Search Ebay for KS0108 I2C adapter by Digole.
You would need to do quite a bit of detective work i.e. to check whether it could drive your module.
Likewise, you would need to check whether the dumb 16-bit Port Expander project would need some extra software to work with your LC7891. Note that this method will be very SLOW.
The ST7920 modules and ST7920 libraries are all ready to use. Unless you have hundreds of free LC7891 displays, it will be quicker and cheaper to just buy ST7920.
David.
david_prentice:
They are not suitable for your display... you would need to make it yourself... it would require a LOT of effort on your part...
LOL - Thanks for that David (and all the other info and suggestions). That's all I needed to hear to put me off the idea altogether. I will see if I can get it working with the 18 pin interface, just for the satisfaction of getting it running, and then most likely retire it to my 'might come in useful one day' box 
The alternative displays are available for around $10 on ebay - I might treat myself to one when I get too frustrated by my 20x4 character display's limitations.
Cheers
Graham
I would simply get it running on a Uno or Mega. I am sure that someone has a regular parallel library for it.
It will be much like a KS0108 project.
I have often thought about the intelligent backpack approach. But with the advent of cheap Chinese PCF8574 adapters, no-one would be interested for a 16x2. Just look at the Digole adapter sales.
The monochrome 128x64 LCD looks rather sad compared to a full colour TFT display.
David.
TFTLCDCyg:
See this work...
Whoosh!
Ha ha - that stuff went way over my head - I am sure I'd pick it up eventually, but think I would probably need a couple more years experience, and reading and re-reading all Nick's info many many times, before I would even consider going down that route!! 20 years ago, I'd probably have thought it a great project to pursue until I understood every detail - but now, life is too short - I'll take the quick easy option every time
Thanks for taking the time to offer up the potential solution though - much appreciated.
Cheers
G
david_prentice:
The monochrome 128x64 LCD looks rather sad compared to a full colour TFT display.
Even more so against a 35" 4K curved screen monitor (not that I can afford one of those)
My TV is 21 inch with vacuum tube CRT. Which still works fine.
My PC has a 24 inch flat TFT screen. I am not sure whether a bigger screen would fit on my desk.
David.