TXD: the sending end , generally expressed as their transmitter, normal communication must be connected to RXD another device .
RXD: the receiving end, generally expressed as their receiving end, the normal communication TXD must be connected to another device.
Itself when normal communication TXD RXD devices connected forever !
Collected spontaneously : RXD when normal communication to other devices connected TXD, so if you want to receive data transmitted by its own name suggests , it is their own to receive data transmitted , which is directly connected to its own TXD RXD, used to send and receive test itself is normal, is the quickest and easiest test method, when a problem first do the test to determine whether a product failure. Also known as the loopback test .

Level logic:
TTL level: typically binary data representation , +5 V equivalent to the predetermined logical 1, 0V is equivalent to logic 0, the system is called a TTL signal is positive logic
RS232 level: -12V used to -3V, equivalent to a logic 0, +3 V to +12 V logic level is equivalent to logic 1 , negative logic

Features :
1, the core module from the module using the HC-05 , leads interface includes VCC, GND, TXD, RXD, KEY pin , pin-out Bluetooth connection status (STATE), not connected to the output low , after connecting the output high
2, led indicate Bluetooth connection status , Bluetooth connection means no flash , slow flash indicates enter AT mode , double flash indicates Bluetooth is connected and open ports
3, bottom set anti-reverse diode with 3.3V LDO, the input voltage is 3.6 ~ 6V, when unpaired current of about 30mA, the pairing of about 10mA, the input voltage must not exceed 7V!
4, the interface level is 3.3V, you can directly connect a variety of SCM (51, AVR, PIC, ARM, MSP430 , etc. ), 5V microcontroller can also be connected directly , not through without MAX232 MAX232!
5, open to 10 meters effective distance ( power rating of CLASS 2), more than 10 meters are possible, but do not make this connection to ensure the quality of distance
6, after the pair when using full-duplex serial port , without having to know any Bluetooth protocol support 8 data bits, 1 stop bit, parity can be set communication format , which is the most common communication format , not support other formats.
7, can be pulled 34 feet into the AT command mode to set parameters and query information
8, small size (3.57cm * 1.52cm), chip production plant to ensure the quality of the patch . And set transparent shrink tube , dust and beautiful, and there is some anti-static capabilities.
9, can be switched via AT commands as master or slave mode , the device can be connected via AT commands
specified
10, support from the Inter- standard baud rate 4800bps ~ 1382400bps

Usage:
After pairing just as the same as using the serial port baud rate can be fixed , so long as it is fixed baud , 8 data bits, no parity , communication format of serial devices can be wired directly to the serial port and replace the original do not need to modify the program . Such as data acquisition , smart car , serial printers, dot matrix screen control , such as outdoors .
Paired with a computer : fit between computers via Bluetooth serial communication with the device , using the same method and serial
Paired with the phone : Good room phone via Bluetooth serial communication with devices using the same method and serial
Paired with a Bluetooth Host : For two devices directly via Bluetooth serial communication, such as between the microcontroller and microcontroller serial cable with microchips , etc., using the same method and serial

Flexible use:
Baud rate conversion, because the receiver and the sender can choose their own baud rate, in a small amount of data when you can use as a device baud rate conversion.

Packing included: 1 x Bluetooth Transceiver Module + 1 x wire harnesss