1.1 Tips (Very important) :
TXD: sending end, generally expressed as its own sending end, normal communication must be connected to the RXD of another device.
RXD: receiving end, generally expressed as their own receiving end, normal communication must be connected to the TXD of another device.
Normal communication when the TXD itself is always connected to the device RXD!
Self-absorption: Normal communication TXD RXD connect other devices, so if you want to receive their data, as the name implies, is receiving themselves to send data, is directly connected to the RXD TXD itself, that is, used to test whether the sending and receiving of normal itself, is the most simple test method is the fastest, when problems arise first do this test to determine whether the product failure. Also known as loop testing.

1.2 Level logic:
TTL level: usually the data is expressed in binary. It is specified that +5V is equivalent to logic "1" and 0V is equivalent to logic "0". It is called TTL signal system and positive logic
RS232 level: adopt -12V to -3V, equivalent to logic "0", +3V to +12V logic level, equivalent to logic "1", is negative logic

1.3 Product Features:
1, the core module uses HC-05 from the module, the output interface includes VCC,GND,TXD,RXD,KEY pin,  connection status pin (STATE), the output is low if not connected, the output is high after connected
2. Led indicates the  connection status. Quick blinking means no  connection; slow blinking means AT mode; double blinking means  is connected and the port is opened
The bottom plate is equipped with anti-reverse connection diode, with 3.3V LDO, the input voltage is 3.6-6V, the unpaired current is about 30mA, the paired current is about 10mA, the input voltage is prohibited to exceed 7V!
4, interface level 3.3V, can be directly connected to a variety of microcontroller (51, AVR, PIC, ARM, MSP430, etc.), 5V microcontroller can also be directly connected, without MAX232 can not go through MAX232!
5, open effective distance of 10 meters (power CLASS is CLASS 2), more than 10 meters is also possible, but the connection quality of this distance is not guaranteed
6. After pairing, when the full-duplex serial port is used, there is no need to know any  protocol. It supports 8-bit data bit, 1-bit stop bit and parity check communication format, which is also the most commonly used communication format, and other formats are not supported.
7. You can enter the AT command mode by raising 34 feet to set parameters and query information
8, small size (3.57cm*1.52cm), factory SMT production, to ensure the quality of SMT. And set transparent heat shrinkable tube, dustproof and beautiful, and has a certain anti-static ability.
9. Switch to host or slave mode by using THE AT command, and connect to the specified device by using the AT command
10, support from 4800bps to 1382400bps between standard baud rate

1.4 Product Usage:
After pairing, the serial port can be used as a fixed baud rate serial port. Therefore, as long as the serial port device is in the communication format of "fixed baud rate, 8 data bits, no parity check", it can directly replace the original wired serial port without modifying the program. Such as data acquisition, intelligent car, serial printer, outdoor dot matrix strip screen control, etc.
Pair with computer: suitable for computer and device to communicate through  serial port, the use method is the same as serial port
Pairing with mobile phone: suitable for communication between mobile phone and device through  serial port, the use method is the same as serial port
Pairing with  host: it is suitable for two devices to communicate directly through  serial port, such as between single chip microcomputer and single chip microcomputer, wired serial port and single chip microcomputer, etc. The use method is the same as serial port

Flexible use:
Baud rate conversion, because the receiving end and the sending end can choose their own baud rate, in the case of small data volume can be used as baud rate conversion equipment.

2.1 How to connect  module to computer (effective in slave mode)
Here is an example of pairing it with a  computer:
First, power on the  passthrough module, and then the LED flashes. Open "My Location" and click "Search for devices in the valid range".

The system searches for devices with the default device name "linvor" (modified name if modified, such as "jiayuanelectron"), double click or right click and choose "add  device".

Enter the pairing password (default: 1234),

Click "Next". If the password is correct, the connection between the computer and the passthrough module will be established. If serial port device has not been installed before, the system will automatically install the driver and generate a virtual serial port

Click Config, select the appropriate COM port,

I can only choose COM5 here, which is the serial port for computer operation after connection. For example, WHEN I open com5 here, the LED of module will change from quick flash to double flash. At this time, you only need to use  module as the serial port of fixed baud rate of computer, but it is wireless.
Tips:

1. The supply voltage must be 5V, not 3.3V

2. Do not connect the pin of the power cable to the data cable. Confirm it carefully before connecting the cable

3. The LED must enter the slow blinking mode before the AT command test

 

4. After each AT instruction is input, you must press enter to send it

5. If OK cannot be returned, swap RXD and TXD

6. Do not tear the heat shrinkable tube or weld it by yourself. Otherwise, the warranty and return and replacement service will be waived

 

7. The RXD and TXD on UNO cannot be used to connect  module for AT instruction test