I2C with Arduino Mini Pro: Address trouble

Dear all,

Recently I bought an Arduino Mini Pro 328 - 3.3V/8MHz (Sparkfun). I started to program it with this using the following connection:

CP2102 || Mini Pro 3.3v ---------> VCC GND ---------> GND TX ---------> RX RX ---------> TX DTR ---------> GRN

As long as I upload classic blink script or similar, Arduino works well. My project is connect a GPS module and display latitude, longitude and other infos on OLED display like this one. In order to use I need of I2C address, hence I used I2C scanner but it stuck to scanning without show any information. This happens in presence or not of screen (doesn't display either "Not I2C device found"). I checked twice the wiring between OLED and Arduino and I think it's right:

OLED || Arduino SDA ---------> A4 (SDA from official pinout) SCL ---------> A5 (SDA from official pinout) VCC ---------> VCC GND ---------> GND

I can not get on top of this issue. Could you help me, please?

P.S. The programmer is AVRISP mkII, I don't know if is important.

Does your OLED library say its for that controller? What's the name of the library?

Are you saying that the I2C scanner hangs even if you disconnect everything from A4 and A5 on the mini, including the display?
The description of the display you have linked is in poor English, but from what I understand, it does not conform fully to the I2C specification and you have to download some additional software. This may cause also cause a problem for the scanner.

Yes I2C scanner hangs even if I disconnect everything from A4 and A5 on the mini

Plenty of tutorials suggest which can be used the library from Adafruit.

Looking description on Sparkfun: "The latest and greatest version of this board breaks out the ADC6 and ADC7 pins as well as adds footprints for optional I2C pull-up resistors! We also took the opportunity to slap it with the OSHW logo." Do you think which two footprints are in the small pad close to A5 as in picture?

If yes do you believe it's necessary solder two pull-up resistors, let's of 4.5k?

No one can help me?

The two pairs of solder pads to the the right of the A5 hole can be used for the optional pull-up resistors. The right hand side of each pair is connected to Vcc. The left hand side of the top pair is connected to A5. The left hand side of the bottom pair is connected to A4.

You can, of course locate the pull up resistors elsewhere if you cannot manage smd component soldering.

The I2C scanner should give the following output if nothing is connected.

I2C Scanner Scanning... No I2C devices found

If you are not getting that far, may be it is something simple. The version of the I2C scanner I used for the above test writes to the serial monitor at 9600 baud.

Even if I haven't nothing connect the result is following (at any baud rate):

I2C Scanner Scanning...

Nothing else... I don't know, could be a corrupted bootloader? :confused:

The scanner hanging with nothing connected can be caused by shorts between A4/A5 or between one of them and ground. Check carefully for any bridging or test between the pins with a multimeter when everything is disconnected and power is off.

Can you provide a photograph which shows the soldering of the header pins or lead wires to the A4 A5 pads?