Bluetooth Foot Pedal for Onsong – an alternative to Airturn ?

Project History!   The intention of this post is to serve as an aide-memoire for a little project I've been working on recently. From time to time, I lead worship at my church, and play acoustic guitar.  For song lyrics / chord charts I use a popular app on IOS called Onsong. A while ago I found an old guitar foot switch unit that started life belonging to a Marshall amp.  I took most of...