I2C requires a pullup on the bus. "master" devices like the raspberry pi have those integrated on their PCB, but if this is not the case (e.g. arduino), this can be solved with this little PCB!

The PCB follows the bitwizard "standard" pinout. The photomodel above was assembled wrong. Sorry. Female connector belongs on the left (looks good so far, right?) but the GND, pin 1 of the connector needs to be nearest the viewer. So you'll get the female on the left, pin1 nearest the viewer (and resistor designators upside down for now). 

Pinout is 1 GND, 2, 3 SDA/SCL, 4 VCC. 

The pullup resistors are 4k7. (If you think we should change that, let me know and why.).