Hi! I wasn't sure if I should put this in the "displays" section or even the "programming questions" section, as it's kind of a hybrid question, but here goes.
I've done a few small projects in Arduino, but I'm still new to a lot of it (as well as electronics in general), so forgive the noobishness. I am working on a project where I want to connect four OLED dispays to my Arduino UNO, and send different text/data to each one. The displays I currently have are cheap ones from China that a lot of people seem to get (http://www.amazon.com/Huhushop-TM-Serial-Display-Arduino/dp/B00JM7SWI4/ref=sr_1_4?ie=UTF8 ), but they only have four pins (VCC, GND, SCL, and SDA) as opposed to 6- or 8-pin displays that I've seen elsewhere. Because there are only four pins, I am led to believe that I2C is the best/only way to communicate with them via the UNO.
I did a test with two of them (using the u8glib, by the way - not sure if that's recommended/how that's different from Arduino's 'Wire' library), and am able to display the same text on each. Which is a start, but I don't know how I would send different messages to different displays via the u8glib. I dug around a lot more, eventually finding the "I2C Scanner" on Arduino's site. Running the scanner, I get the result "I2C device found at address 0x3C !" when I have either OR both displays connected, and "No displays found" if I disconnect both of them. Huh? This tells me that both displays are given the same address, which would mean that I couldn't differentiate between them in my code. If this is the case, is there something I can do to change the address of one of the displays?
As an aside, on the back of the displays there is a box which says "Address select: 0x7A | 0x7B" (see picture). Might this be useful for the Arduino detecting different addresses for the two (and soon to be four) displays, or is it nothing I should concern myself with?
Finally, I have read in many places that a 4.7k 'pull-up' resistor is necessary for I2C devices. This is where my lack of electronics hardware starts to shine. The displays are obviously displaying stuff fine without them, but would that possibly be a reason for not having more than one address show up from the I2C Scanner?
Whew, that was a lot of questions in one! I feel like it's a simple enough request (send data from an Arduino to four OLED displays independently), but actually figuring it out has been plaguing me. If I can provide any additional pictures or information to help clear anything up, let me know. Any help would be greatly appreciated. Thank you!