I'm planning to create a midi trumpet. If it works, I will expand the idea to a midi trombone.
I picked some components from an old matrix printer. Among the stuff there was a piece of PCB holding the three push buttons of the front panel. So I thought of turning it into a trumpet. I just received a pressure sensor, which I'll use. I'm going to create midi events that I send to an old midi synthesizer through a standard midi cable (with DIN connectors). My idea is to attache a tube to the sensor. I'll be blowing in the tube. I might want to make holes in the tube to adjust the amount of pressure that reaches the sensor. And I want the feel of actually blowing, not just pressing air. A certain threshold will create a midi note-on event (or is it called key-down?). First the pressure will determin a pitch, or a frequency. Then I will read the three buttons. I will calculate the nearest tone to this key combination. This tone will be the one that the note-on event will play. I will also create a pitch-bend event to match how much off the pitch the pressure is. And as long as there's a pressure over the threshold, the sound will continue. My controller will read the pressure continuously and create pitch-bend events accordingly. When the button combination changes, a note-off event is created and a new note-on event is prepared and performed. When there's a sound on and the pressure changes enough to activate another tone, a note-off event happens and a new note-on is prepared.
So far I've just planned to have the tube I'll be blowing in. This is far from the real feel of playing a brass instrument! But I'm hoping anyway to create a feeling remotely resembling the playing of a three valve brass instrument. And a synth with a trumpet-like sound will add to the illusion. But I might develop the idea to include a real mouth piece to blow in.
And if it works, I'll continue with a trombone. I'll use electric installation tubes for the slide, a light source (bright white led) and a light depending resistor to measure the slide position. The nature of a trombone requires a greater pitch bend range. Moving the slide while the tone is on only affects the pitch-bend, whereas pushing the buttons on the trumpet creates new note-on events.