I recently bought a handful of these
to play with. So far I'm quite puzzled/disappointed by the result. They seem to work (that is, to be found by an I2C Scanner sketch) just once. After that, any attempt to talk on the I2C bus with this device attached will hang on endTransmission, so I2C_Scanner won't work any more. If I disconnect the device, I2C Scanner starts working again. But the device never works again.
I fear I may be killing them somehow, but can't figure out what I might be doing wrong. I've used a number of other IIC devices successfully, so it's not my first time connecting SDA and SCL :-)
I have tried powering the OLED from the Arduino, and also powering it independently (with a bboard power supply); I've put 4.7K pullups on SDA and SCL. Nothing seems to help. Before investing hours in a big debugging drama, I was wondering whether I've just bought a bum product and no one is having any joy with these devices.
I note that when I2C Scanner did work, it found the device at 0x3D; but the stencil on the module says it should be found at 0x78. This wasn't too reassuring re quality control :-)
Anyway, if anyone else has bought one of these and either found out how to make it work, or gave up and threw it away, I'd like to know :-)