I added a basic breath sensor to the pastry saxophone. It kinda works! The response of the breath sensor is quite slow - I think I need to use something stretchier than a nitrile glove. It doesn't feel sensitive enough to do staccato notes or anything yet.
I didn't get dynamics working with the USB MIDI yet, but on/off breath control works well
The breath sensor works like this guy's video: https://www.youtube.com/watch?v=es92GqYBge0
The black tape all over it is to block out light - I found it was making a big difference to the readings.
I've started printing the mouthpiece and designed the sensor half of the breath sensor. This uses a TCRT5000 IR reflectivity sensor, which shines at a diaphragm clamped between the two halves.
When you blow into the mouthpiece, the diaphragm expands towards the sensor, increasing the amount of IR that's reflected back into it.