I2C LCD connected to a PIC16F micro

[Alexandros81]

Hi!
I have recently purchased an LCD Display from here:
https://www.ebay.co.uk/itm/LCD-Display-Module-LCM-blue-blacklight-Character-1602-16x2-HD44780-3-3V-5V-UK/152214576387?ssPageName=STRK%3AMEBIDX%3AIT&var=451404694759&_trksid=p2057872.m2749.l2649

I also got the interface board that lets you use the display via I2C.
Do you know if thereis  a user guide for the interface board?
What is the I2C Interface protocol for the interface board?

I am connecting the LCD with a PIC16F15345.

Thanks

[mariush]

As the ebay sale says, that's a HD44780 based lcd, so you use those commands.

You can see the name on the chip, PCF8574.... here's datasheet: http://www.ti.com/lit/ds/symlink/pcf8574.pdf
That's a basic  I2C port expander, it creates 8 i/o pins which are most likely connected to your  LCD's RS , RW, EN and probably 4 i/o pins.

So you send the i2c commands to the chip to set some i/o pins as input, some i/o pins as output , then set the pins to some values...  the same commands you'd send if you connected the lcd display directly to a bunch of i/o pins on your micro, you will send them through i2c formatted as the chip wants.

If you don't have documentation, you can use a multimeter to figure out which i/o pins from the io expander IC go to which pins of your lcd display.
you also have on the board pads labeled A0 , A1 and A2 .... those allow you to configure unique i2c address for your board, probably some default address is set if those 3 pins are floating (and if you put a blob of solder on one of those pairs of pads you basically set one bit of the 8 bit i2c ID to 1 or something like that)

[Alexandros81]

@mariush
Thanks. Just a few minutes ago I discovered it was the chip PCF8574T by looking at the picture.
I'll give it a go then!

[JustMeHere]

For about $5 USD, you should be able to find an LCD display that speaks I2C directly.  The actual protocol seems to be "shared" so finding a driver might not be that hard.