Multiple I2C LCD's

Other Hardware Displays
21

Paul__B:
The address pins are tied to VCC - thus the $3F address. The VCC line runs through them but could be modified with some difficulty! (Data)

The +5v routing on that backpack really sucks!

Given that layout I see two ways that aren't so bad:

  1. carefully desolder pin 1 and lift the pin and then solder a small wire on it ground.
    This is a bit dangerous since if the pin bends back down you have VCC to ground short.

  2. two cuts, one/two jumps

  • cut the trace from the pot to pin 3 of the PCF8574
  • cut the trace between pins 1 and 2 of the PCF8574
    (verify this with an ohm meter to ensure the trace is fully cut as it is difficult to get between the pins)

It appears that the VCC header might get power from the back side VCC plane. But if not

  • Solder a wire from VCC to the 2 pin header to restore VCC

  • scrape the solder mask just beyond pins 2 and 3 to expose the ground plane

  • put a tiny solder blob from pins 2 and 3 to the ground plane.

Big takeaway from this, is to carefully look at the product before buying.
I always check the product photos and make sure that what I'm getting matches the photo, and then that it is/does what I need. For i2c backpacks, I better be able to set the contrast and change the address so I have to see the address jumpers and pot on the side of the board that will be facing up when soldered to the LCD.

--- bill

22

Hi, guys I know this is a very old thread but still several newbies in Arduino ask the same question, how to connect two or more I2C LCD to Arduino

Here is post I found online this was a really helpful and worked flawlessly:

I tried to hook two I2C LCDs with Arduino uno and worked like charm.

Have a great day guys.

23


OK, people - it says "TESTED: OK", but does it actually work and did you spot the blunder in the illustration?

Note as ever, the blunder in these designs. The potentiometer should not be connected to 5 V at all - the end should be left unconnected or in fact, connected to the other end because the correct value for the potentiometer would be 1k while connecting both ends to ground reduces the 10k value if you are using that and spreads the workable range of contrast adjustment more widely over the potentiometer range. :grinning:

In fact, it should not be presumed that the contrast value should be the same for any two displays though in practice it will be "near enough" to connect them together.