Getting on the bus: I2C

On top of the serial connection I was using to get the Uno and NodeMCU talking, there is also I2C bus line communications. That is what I need to learn now, in order to be able to master the (PCF8591) DAC module, and build a voice-box around it.

The quick rundown of I2C is that it allows you to connect multiple devices to the 2 designated (Clock and Data) pins of your microcomputer, by assigning a unique addresses to each connected device. Only the specific device who’s door is being knocked on will open it and respond to the Microcomputer, so it is key to know:
1) what the address is for everything connected to the I2C busline.
2) which of the pins on your Microcomputer are your SCL and SDA (They may not be labelled, and layouts can vary by model/manufacturer) I needed to find a schematic/factsheet to find out the NodeMCU has it’s SCL on D1, and SDA on D2

That established, I then connected D1, D2, Power and Ground from the NodeMCU to the PCF8591 module, and ran a diagnostic “I2C Scanner” sketch that I found in an archived Arduino forum from 2016, which informed me that I had something sitting at 0x48. This told me, first, that I was correct about D1 and D2 (hooray) and second that I now had an address that I can send signals to.

What the signal is going to be, and how I’m going to generate it still to be determined… as are the questions of how and where I’m supposed to connect the speaker, but at least I can say that I know I’m going to take the bus to the right address.