Is the backlight on and do you see the initial banner on the display?
when the Arduino powers up?
* i2C Smartie *
* Arduino *
If you do not see this, then there is a library issue, most likely the constructor is incorrect.
That must be corrected before going any further.
If do you see this, then the switch between libraries for the sketch is correct and it something else.
It could be a timing issue because of the sketch using command()
I had a look at the sketch to see what it was really doing.
It is calling command() to send raw lcd commands when it could (and should) be calling library functions to do the same thing. There are lcd library functions to do all the things the sketch is doing and there should be no need to be using a command() function.
The issue with that is that some lcd commands take a considerable amount of time and if another command is sent too soon, things can get screwed up.
The library will do the proper timing when its functions are called but if command() is called, the sketch must handle the timing. (and it isn't doing anything with respect to timing)
fm's library is significantly faster than other libraries so it could result in a timing issue because of the way the sketch is using the interface by calling command() directly. (hence why the command() function was originally private)
If you did see the banner and want to see if it is timing issue you can put a delay in the loop processing and see if that helps.
I would add the delay right at the top of the loop() function.
4 ms should be more than enough to verify if this is the issue.
so add a delay(4); just before reading the serial interface at this line:
rxbyte = serial_getch();
If that clears up the trash on the display, then there is a timing issue and the sketch is violating the lcd timing by using command()
The delay can remain (if everything works with it), or the sketch will need to be fixed to use the lcd functions and stop using the command() interface.
--- bill