Bluetooth HC-05

The standard Bluetooth module for Arduino projects. Once paired it behaves exactly like a wired serial connection, so existing Serial.print and Serial.read code works unchanged over the air — which is why it appears in so many robot control and data logging projects. Unlike the HC-06 it can act as master as well as slave, so two modules can talk to each other directly without a phone involved. Two practical points: it pairs with Android and Windows but not iPhone, and its RX pin is 3.3V and needs a divider from a 5V Arduino. Wireless serial with no changes to existing code; Master or slave mode, unlike the slave-only HC-06; Two modules can link directly to each other; Configurable name, PIN and baud rate via AT commands