Okay, a primer.
Breath controllers are devices you blow into to produce a variable voltage for expression. Breath control (MIDI CC#2) is a very musical way to get expression after you play a note. I have three instruments that have breath controller inputs: a Kurzweil K2500X, Yamaha VL1, and Alternate Mode DrumKAT.
Geoff linked the MIDI Solutions breath controller - MIDI converter (for instruments that don't have inputs) and the TEC USB one, but the first ones I know of were made by Yamaha and are now discontinued. They're all awful - the BC1 required way too much pressure, and the BC2 and BC3 had the feel of an orthodontic appliance. However, you can put a tube into the BC2/3 without using its ****e mouthpiece, and then it's actually quite good.
A company called Hornberg makes an absolutely beautiful breath controller. It's not cheap, however - nor could it be, given that it's a high-quality musical instrument:
https://www.hornberg-research.de/ind...er-products-en
I've been involved with two breath controller products. One was a hardware one made by an engineer I teamed up with, but that project petered out after only a handful of sales.
The other is an iPad program called Blowfinger, which uses wind noise across any cheap mic (for example a $3 iPhone headset mic, preferably with the earpieces cut off) to produce the varying voltage, which gets sampled and translated into MIDI values.
Blowfinger - the "finger" part of the name - can work as a wind controller or just a breath controller. Wind controllers are like the thing TimR described, most likely a Yamaha WX-11. (Bummer that your impression of them was tainted, because wind controllers are wonderful instruments.) The best-known wind controllers are Akai's EWI series and the Yamaha WXs, but there are others.
Wind controllers work like acoustic wind instruments - you hold down combinations of keys and blow into them, only they send MIDI notes (and some have internal synths now). Blowfinger has a familiar keyboard you touch on the screen, or it has touch pads on the screen that you finger using standard Boehm fingering system.
Or you can play it - as well as the Akai EWI - using a modified recorder fingering system, which is what I use since recorder is my first instrument. While the WX-11 and WX-5 have keys like a clarinet or sax, the EWIs have touch pads, which is totally natural for a recorder player but a little harder for a sax player to get used to. (The touch pads are capacitance-sensitive, like elevator buttons.)
Wind controllers are incredibly satisfying to play if you have the right synth paired with them. I use a 24-year-old Yamaha VL1 most of the time with my EWI 3020 - an awesome instrument if you exploit its unique sounds rather than its emulations - and I also like the analog synth contained in the EWI's brain (the 3020m rack box).
But unlike breath controllers, wind controllers aren't usually good for working with modern sample libraries, which are set up for keyboard control. Usually you switch articulations - samples of different playing techniques - with keyswitches, which are like program changes triggered from notes in an unused part of the keyboard.
So for example if you're playing long connected notes on a violin and then you want a hard, short attack, you'd switch to a staccato sample program for that note. That's hard to do with your fingers on a wind controller; now picture a library with over a dozen keyswitched articulations.
Wind controllers are designed to shape the notes while you're playing them, rather than switching articulations. But you can use breath controllers with samples very effectively to shape the dynamics and brightness in real time, by mapping them to volume and filtering/eq.
Anyway, I have a BC2 that isn't working, and I want to fix it.