HC-04 Bluetooth Module (SPP/BLE) and HC-T Test Adapter (USB-to-TTL converter)

HC-04 Bluetooth serial communication module is a new generation of dual-mode digital transmission module based on classic Bluetooth SPP (V2.1) and BLE.
~ Product page
~ HC-04 Specification (v2.4)

HC-T Test Adapter (USB-to-TTL converter) can be used with HC series modules.
~ Product page

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First Test HC-04 Bluetooth SPP/BLE Module

It's my first test on HC-04:
- A Raspberry Pi is used as test host, via RP2040 dev. board as USB-to-Serial adapter, connect to HC-04. HC-04 act as slave in default.
- Test with AT-command.

- And communicate with Android device with HC's Android Bluetooth Serial Assistant App, in BLE mode and Classic Bluetooth SPP mode.


For the USB-to-Serial adapter implemented with RP2040, refer to the post Serial communication between two RP2040 (Arduino Framework). Both Serial_9600N81_SH1107.ino (with SH1107 OLED) and SerialPassthrough_9600N81.ino (without display) can be used.

Connect RP2040 board with HC-04:

	HC-04		RP2040/Pico
	=======================
	KEY		no connection
	VCC		3V3
	GND		GND
	TXD		GP1(RX)
	RXD		GP0(TX)
	STATE		no connection

Use a Android device used as master to connect to HC-04 (default in slave role).

Install HC's Test App on Android device:
Visit https://www.hc01.com/downloads
Select 测试工具
Download and install 安卓蓝牙串口助手（支持蓝牙2.0、BLE）Android Bluetooth Serial Assistant (support Bluetooth 2.0, BLE)

In test host (Raspberry Pi) side, Arduino IDE's Serial Monitor is used to communicate with HC-04. By default HC-04 is set 9600N81 mode.

Exercise:
~ Bluetooth serial communication between RP2040 using HC-04 Bluetooth Module, in BLE/SPP mode.