gmcmurry:
But I assume one would still need to make sure the two LCDs do not have the same physical address; ie bridge the A0 jumper on the BackPack. I think most of these we find will have all the address jumpers open.Correct?
Greg
Correct.
If using more than one LCD device at a time, the i2c addresses on each device must be unique.
While most LCD modules have jumpers or solder pads and they are typically open when shipped, not all LCD backpacks have the same default i2c address nor the same configurable address range.
This is because there are two different address ranges for the PCF8574 chips.
0x20 to 0x27 and 0x38 to 0x3f.
So depending on which chip is on your backpack the default address and address range may be different.
Also, some backpacks are wired to have open jumpers as high and some are wired to have open jumpers as low.
So it isn't always obvious what the default address is or what it will change to when bridging a jumper.
If you are unsure about the address of your backpack, run the included I2CexpDiag sketch and it will tell you the address.
(on serial port and on the LCD itself)
You can even hookup up multiple LCD devices at a time and it will test all the devices it can locate.
--- bill