LCD4004A Support

[gmitch64]

I'm having issues getting the library to work with a 4004A LCD screen (4 lines of 40 columns).

I'm wondering if the library should support a 4004A LCD screen?
If it does, is there a preferred I2C module to connect up the screen with? I'm using a standard PCF8574T module, and just using Select0 on the LCD (so I'm only expecting half of it to work at the moment). Is there another/better known good module for the 4004A screens that I should use?

G

[bperrybap]

I've considered adding support for this a few times.
The main reason I haven't is I really don't like that display because it really is two separate independent displays that are controlled separately.
I don't ever intend to support it directly in the hd44780 library.
That said, I have considered writing a wrapper template class that allows joining two displays to work as a single logical display.
It essentially offers the same functionality but IMO, it is better way to handle this funky display.
A wrapper virtual multi LCD class could work with any existing hd44780 i/o class or any existing LiquidCrystal API compatible library.
It could support the 4004 by treating it as two separate displays that operate as one.
i.e. virtual display would be told about the two displays and their geometry and what the desired virtual geometry is.

But truly supporting the 4004 is more difficult than it may first seem if it is to fully operate the same way as the "normal" hd44780 displays.
There are things related to cursor status, cursor positioning, scroll/shift modes, and wrapping that have to have s/w to emulate things to make it work the same as a "normal" display.
So isn't as simple as just being able to write the correct lcd, and address the cursor position, there is quite a bit of hd44780 state stuff that has to tracked in s/w to try to make the 40x4 display behave the same was the "normal" displays.

For I2C using something like an i/o expanded can be done but it will take more than just 8 i/o pins to control the two LCDs and the backlight.
If you don't need to control the backlight, then you could use a PCF8574 backpack steal the backlight pin to control the other E signal and just hard wire the backlight be on.