HM-10 BLE module
Known-good module type for iOS because it exposes BLE serial-style service and characteristic UUIDs (FFE0 / FFE1).
Wiring and compatibility
Use BLE serial and cross TX/RX
The iOS app connects over Bluetooth Low Energy. Your microcontroller sees ordinary serial bytes through the BLE module's UART pins.
UART wiring checklist
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Cross TX and RX
The module's TX pin goes to the microcontroller RX pin. The module's RX pin goes to the microcontroller TX pin.
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Share ground
The module and microcontroller must share GND or the signal levels do not have a common reference.
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Check voltage before power
Many BLE modules are 3.3V devices. Check the board label or datasheet before connecting power or logic.
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Avoid upload conflicts
Pins 0 and 1 on Uno-style boards are also used for USB upload and Serial Monitor. Disconnect the BLE module while uploading if those pins are in use.
Primary Serial fallback for Uno-style boards
#include <BluetoothSerialConnect.h>
// Use this only when the BLE module is wired to pins 0 and 1.
// Verbose logging is disabled because Serial is also the module port.
BluetoothSerialConnect serialConnect(Serial, false);
void setup() {
serialConnect.begin(9600);
}
void loop() {
serialConnect.readSerial();
}
SoftwareSerial on spare pins
#include <SoftwareSerial.h>
#include <BluetoothSerialConnect.h>
// Put the BLE module on two spare pins (Uno/Nano: RX = 10, TX = 11).
SoftwareSerial bluetoothModuleSerial(10, 11);
BluetoothSerialConnect serialConnect(bluetoothModuleSerial, true);
void setup() {
Serial.begin(9600);
// Start the SoftwareSerial port yourself; begin() below only opens hardware UARTs.
bluetoothModuleSerial.begin(9600);
serialConnect.begin(9600);
}
void loop() {
serialConnect.readSerial();
}Arduino Uno / Nano
Use primary Serial pins 0 and 1 with verbose mode off, or choose a board with a spare hardware UART.
Teensy 3.1 / 3.2
Hardware serial ports make wiring and upload flow cleaner.
HC-05 / HC-06
Classic Bluetooth modules are not supported by the iOS app.
Other BLE UART modules
They may work if service and read/write characteristic UUIDs match the app settings.