I plan to use this OLED display that has the following spec:
from the seller:
Type OLED Display
Interface I2C
LED Colour White
Resolution 128x64
Viewing Angle 160°
Power Consumption 0.08W Voltage 3-5V DC
Working Temperature -30 to 70°C
Driver IC SSD1306
Dimensions 27x27x4mm
Now, most of the time I will use UNO that uses 5V logic.
In which case Vcc=5V and both I2C lines are also matching 0 to 5VDC levels.
My question is - what will happen to the display if I try Vcc=3.3V but the I2C logic be of 5V?
Can I mix the two voltage levels safely?
Best to use the guidance of the manufacturer's datasheet. Adafruit has the SSD1306 datasheet in pdf on there server. It says:
VDD = 1.65V to 3.3V for IC logic
Similar for OLEDs based on SSD1309. May work at 5V logic, but may not be within manufacturer's specs. Some OLED module manufacturer's provide level shifting for 5V operation (see Adafruit "5V Ready" OLED products), so check the module's PCB for level shifting circuits. Adafruit provides a schematic of there level shifting approach.