https://www.eevblog.com/forum/projects/breath-controller-for-synths-w-bc-input-need-design-help/

http://www.tecontrol.se/products/usb-midi-breath-controller

https://www.hornberg-research.de/index.php/en/breath-controller-products-en

http://www.mrtaudio.com <http://www.mrtaudio.com/>

http://new-type.asia/ntbc_01_en.html

http://kelfar.net/bck-1-breath-controller/