Because you are using iPhone you will need to use bluetooth BLE. An HM-10 bluetooth module on a 5v breakout board and a Pro Mini are not only pretty small but also about the same size. A bare HM-10 is a 3.3v device and you can get 3.3v Pro Minis.
Because you are using iPhone you will need to use bluetooth BLE. An HM-10 bluetooth module on a 5v breakout board and a Pro Mini are not only pretty small but also about the same size. A bare HM-10 is a 3.3v device and you can get 3.3v Pro Minis.