On the Arduino Nano, pin A4 is SDA and pin A5 is SCL for the I2C bus.

Today I moved the prototype from breadboard to veroboard. So there's a new photo.

I'll have to add more to the veroboard so I cut it big so I can add:

• TX/RX from UART to R-Pi
• Voltage regulator to take 12v in and give 3.3/5v out to power the Arduino Vin.