Hi,
Is it technically possible to connect more than 2 (say 3 or 4) LCD 1602 units with I2C backpacks to an Arduino Mega 2560 R3?
I know how to change the LCD address on my backpacks by soldering between the pads A0/A1/A2, and I have successfully connected 2 such LCD units to my Mega using the 2 available sets of SDA/SCL pins, as shown in the attached picture.
I seem to have run out of SDA/SCL pin pairs, so is it possible to attach any more such LCD units to the Mega, and if so, how?
Thanks.
Okay,
I figured this out, after realizing from a comment on the forum that the SDA/SCL pin pairs are connected in parallel on the board.
So I created an SDA and an SCL bus from the board and connected my 4 displays in parallel off these buses.
Of course, the 4 LCD's need to have different addresses. Note that I am drawing the power and ground off an external +5V and GND bus.
Solved.
Got that figured then.
Now the backlights on most of these LCD displays draw no more than 20 mA, so four of them at 80 mA should be reasonably within the capability of the Arduino to supply - as long as nothing else is drawing more than a few mA and certainly if it is powered by USB.
For this many, you do not need a separate supply and it will be less trouble to power them from the Arduino Vcc.
There is at least one other possible problem. Many I2C adapters, including the ones in your picture, have pull-up resistors on the pc board. This is really convenient when you are using only one device but may be a problem when you are using several.
The problem is that on each line (SDA and SCL) the resistors on all of the boards are in parallel thus lowering the effective pull-up resistance. You may have to remove the pull-up resistors on all except one of the boards.
Don
