The UDA1334A is an I2S amplifier - it does not use analog inputs, it only has digital audio input support! Don't confuse I2S with I2C, I2S is a sound protocol whereas I2C is for small amounts of data.
There are 3 required data pins used on the Pi for I2S Audio, and 2 pins that are optional but good to know about.
- Pin #18 - I2S Clock
- Pin #19 - I2S LR Clock (also sometimes called WS Clock)
- Pin #21 - I2S Data Into the amplifier (out from Pi)
- Pin #16 - Mute pin, you can use this to mute the output complete, sometimes helpful if you want to keep audio running and then turn it on/off with a switch or button.
- Pin #20 - I2S Data Out from a microphone (into the Pi)
You don't have to do anything with that info other than know that pins 18, 19, 21 are not available for to use and pin #16 is by default used for muting. Pin #20 isnt used by the bonnet, but its handy if you plan to connect some other I2S microphone in.
The output from the DAC is into a standard 3.5mm stereo headphone jack. Output is 'live level' (approx 1Vpp). You can plug in a set of headphones but the output isn't designed for driving low impedance so you will get some distortions at loud volume. The output is fully AC coupled with 47uF capacitors, sleeve ground is connected to the Pi ground.
There's also a breakout slot for soldering in dual/stereo RCA jacks, not included with the bonnet.
Or you can just use one of these cables: