Collection of sample Bluetooth Low Energy applications for iOS, Android, ESP32 and Arduino Nano 33 IoT.

The apps implement basic BLE communication:

• Central scans for Peripheral and connects to it
• Central reads a value from Peripheral
• Central writes a value to Peripheral
• Peripheral notifies Central that a value has changed

Each BLE Central is compatible with each BLE Peripheral, because they use the same service and characteristics UUIDs.

Android BLE Central	iOS BLE Peripheral

To run and see it working, you need 2 physical devices supporting Bluetooth Low Energy:

• one device for BLE Central app - Android, iOS, ESP32 or another supported device
• another device for BLE Peripheral app - Android, iOS, ESP32 or another supported device

...and some development tools:

• Android Studio - for Android project
• Xcode - for iOS project
• Arduino IDE with ESP32 board installed - for ESP32
• Arduino IDE with ArduinoBLE library - for Arduino Nano 33 IoT

Peripheral (also called Slave or Server) works similarly on all platforms:

• Advertises a service with our UUID (see Table of UUIDs)
• The service contains 3 characteristics:
  • for read - has only read permission (see Table of UUIDs)
  • for write - has only write permission (see Table of UUIDs)
  • for indication - supports only indications (see Table of UUIDs)
• Allows the user to change the string value of the characteristic for read
• Allows the user to change the string value of the characteristic for indicate
• Allows the user to send an indication with updated string value to the connected Central

Note 1: technically characteristics can have any amount of permissions (read, write default, write without response, notify, indicate), but in this project each characteristic has only one permission for simplicity.

Note 2: indication is a notification with response - Peripheral notifies, Central confirms that notification received.

Central (also called Master or Client) works similarly on all platforms:

• Scans for Peripherals which have a service with our UUID (see Table of UUIDs)
• Connects to the first found Peripheral
• Discovers services and characteristics of the connected Peripheral
• Subscribes to indications of the "Characteristic for indicate" (see Table of UUIDs)
• Allows the user to disconnect from Peripheral
• Allows the user to read a characteristic value (string) from Peripheral
• Allows the user to write a characteristic value (string) to Peripheral

Android BLE (usually articles cover only BLE Central role):

• The Ultimate Guide to Android Bluetooth Low Energy by PunchThrough
• Making Android BLE work by Martijn van Welie
• (Talk) Bluetooth Low Energy On Android by Stuart Kent

Android BLE Peripheral role (less popular topic):

• How to Advertise Android as a Bluetooth LE Peripheral by Paul Trebilcox-Ruiz
• Bluetooth GATT Server Sample by Android Things

iOS:

• Transferring Data Between Bluetooth Low Energy Devices by Apple (with sample code, Central and Peripheral)
• The Ultimate Guide to Apple’s Core Bluetooth by PunchThrough

LightBlue: for iOS, for Android

BLE Scanner: for iOS, for Android