The AUX connector
The AUX connector on the MidiStick can be used for outputting audio for testing, as an input for a E-STOP button or for the data connection during a firmware recovery. The pinout is shown in the image on the bottom of the page. (I have no idea how to make the image show up small enough to put it here sorry 😞)
The connector is a JST-XH one, that can be found cheaply on ebay/amazon/aliexpress so if the cable I included is not enough you can make your own. I recommend getting a set with different sizes and a crimping tool if you don't have one already, as they are used all over the place.
The pin has a 10k pull-up to 3.3V, an impedance of 470 ohms and is protected by a tvs diode so it ESD is not a concern. But it can't really provide a lot of current.
I recommend using the output impedance as part of a voltage divider if you want to send this to an audio pin, as the 3.3Vpp are outside the ~2Vpp of normal line level. For this you should use a resistor in the range between 220-1000 ohms in parallel with the audio output, the lower you make this, the more quiet the signal will be.
Connect the E-STOPs NC (normally closed) position to the pins of the stick. An open between the lines will disable the output.
Connect a normal UART transmitter device so the data going to the MidiStick (TX on the UART bridge) connects to the signal connection and then the grounds of the two devices together. To recover the firmware follow this guide
