I have a project where a pro-mini acts as a primary controller for a hydroponics setup. Part of that setup is an I2C LCD with buttons that lets you set (among other things) the lights-on and lights-off times. I want to add a Wemos D1 Mini that communicates with the pro-mini on its shared bus to the LCD to control the light cycle whereby the pro-mini tells the D1 what the on- and off-times are, then the D1 monitors the time from the internet, and alerts the pro-mini at the proper times.
So I'm wondering how you go about doing that, considering the D1 mini is not 5V tolerant. Since the pro-mini is running at 5V, I'm guessing simply pulling SDA and SCL up to 3.3V wouldn't be enough since all the communication coming out of the pro-mini would still be 5V, right? Or does all the communication happen though pins being pulled low, meaning this would work?
Alternatively, would putting the whole I2C bus on a voltage divider like pictured below be sufficient? This image shows SDA and SCL coming from the pro-mini, going through the voltage divider after being pulled high to 5V, then going on out to the rest of the components on the bus. VCC = 5V.