Arduino code for a RedBear Nano v2 to allow it to send serial messages from external sensors to an iOS device via Bluetooth BLE.
Read more about the RedBear BLE Nano v2.
They have a good GitHub repo for getting started.
Including a guide for installing the boards library in Arduino.
Here's how I wired it in for a Water Quality sensors project.
See the accompanying iOS app repo: https://github.com/sighmon/WaterQualitySensorsiOS