Do I have to switch my Qwiic Pro Micro from 5V to 3.3V to use any of the Qwiic sensors which are rated at 3.3V?
If so, do I have to run my Qwiic Pro Micro at 8 MHz somehow, instead of 16???
Hello bobzooki,
In the [schematic the I2C lines are pulled up to 3.3V by default. This ensures that they’ll work with all of our 3.3V Qwiic products.](https://cdn.sparkfun.com/assets/4/4/f/2/a/Qwiic_Pro_Micro_V2_0_USB_C_Schematic.pdf)
Hi bobzooki.
To add to TS-Brandon’s post and to explain in a bit more detail what makes this OK:
The way I2C works is your micro controller doesn’t apply any voltage to the SDA and SCL pins, that’s supplied by your pullup resistors and every Qwiic board includes pullups that connect to 3.3 volts.
When your micro controller wants to communicate over I2C, it grounds the SDA and SCL lines in pulses rather than applying 3.3 or 5 volts. That lets you connect a 3.3 volt I2C/Qwiic device to a 5 volt micro controller without any issues. When a low needs transmitted, the line is pulled to ground and when a high needs transmitted, we just stop grounding the line.
As long as you’re powering your Qwiic device with 3.3 volts, (the correct voltage for Qwiic anyway) and you don’t have another 5 volt I2C device connected to the same I2C/Qwiic bus, it’s safe to use a 3.3 volt Qwiic device with a 5 volt micro controller.
In short, with I2C/Qwiic the clock and data lines go between ground and whatever your pullup voltage is and Qwiic devices set the pullup voltage to 3.3 volts by default so everything is safe. 