Here we are going to look, how
we can connect two Bluetooth serial modules.
Here I am taking the example of Bluetooth module HC 05
because it is a widely using Bluetooth serial module (Bluetooth SPP). Serial port
Bluetooth module is 3Mbps Modulation with complete 2.4GHz radio transceiver and
baseband.
 |
| HC 05 Module and important pins |
Some of other features of this module are
- ·
Up to +4dBm RF transmit power
- ·
Low Power 1.8V Operation ,1.8 to 3.6V I/O
- ·
Default Baud rate: 38400, Data
bits:8, Stop bit:1, Parity:No parity,
Data control: has. Supported baud rate:
9600,19200,38400,57600,115200,230400,460800.
- ·
Given a rising pulse in PIO0, device will be disconnected.
- ·
Status instruction port PIO1:
low-disconnected, high-connected
- ·
PIO10 and PIO11 can be connected to red and blue led separately.
When master and slave are paired, red and
blue led blinks 1time/2s in interval,
while disconnected only blue led blinks 2times/s.
Auto-connect to the last device on power as default.
- ·
Permit pairing device to
connect as default. Auto-pairing PINCODE:”0000” as default Auto-reconnect in 30
min when disconnected as a result of beyond the range of connection.
- ·
Bluetooth protocal: Bluetooth Specification v2.0+EDR
- ·
Frequency: 2.4GHz ISM band
- ·
Modulation: GFSK(Gaussian
Frequency Shift Keying)
- ·
Emission power: ≤4dBm, Class 2
- ·
Sensitivity: ≤-84dBm at 0.1%
BER
- ·
Speed: Asynchronous:
2.1Mbps(Max) / 160 kbps, Synchronous: 1Mbps/1Mbps
- ·
Security: Authentication and
encryption
- ·
Profiles: Bluetooth serial
port
- ·
Power supply: +3.3VDC 50mA
- ·
Working temperature: -20 ~
+75Centigrade
- ·
Dimension: 26.9mm x 13mm x 2.2
mm
You can easily connect your android
phone/ PC to this HC 05 module. For that, just power ON your HC module, then switch
on your PC/Phone Bluetooth. Now search from
your PC or Android phone, it will show the device name. Select pair option and
give pair password. The default password might be 1234 or 0000. If everything
is OK, then your HC-05’s pair LED (if
any) will glow.
But if you want to connect to two embedded system device
using HC-05 we want to do following tricks.
How to connect two
embedded system project using Bluetooth module
HC-05
comes from the factory as SLAVE mode; that means a master (Android/PC) can
easily manage the connection between the
HC slave connections. But if you are
connecting two HC modules, for example, you want
to connect two embedded system projects,
you should do some tricks!. Otherwise, it will not works.
The reason is that,
Initially Both of the modules are in slave configuration and slave-slave
(or master-master) communication is not possible. So we want to change the mode of one Bluetooth module for the
communication.
For this you need
following tools
- 1.
TTL to RS232 converter
- 2.
Terminal Software (you can download it from www.pravysoft.org website)
Normally
HC-05 modules are TTL module means if we directly connected this module to PC
serial port the RS232 signals from PC will damage our module. So you should use
a
TTL to RS232
converter. If you are
familiar
with MAX232
chip, you can make this using
simple circuit (visit
http://pravysoft.blogspot.org
) for
making this module.
 |
| HC 05 With built in RS232 PORT |
Now you need
to connect the RS232 connector to your PC. Latest PC’s does not have
serial port (DB9 pin), if so you need to use RS232 to USB converter module, note that you should install proper drivers to
work USB to serial converter. You can see the
corresponding ports of USB to serial converter in DEVICE MANAGER as shown in
the figure.
 |
| Serial to USB convertor (Black) and HC 05 module |
 |
| Device Manager window to find serial port number |
If the port number is greater than COM7, change the port number to a lower
one. Otherwise, the terminal software won't detects the PORT
Then
take your HC05 module and feed a 3.3V voltage for its KEY pin (Please
see the first figure).
Some HC05 RS232 modules are
coming with KEY PINs, for that you just
place a jumper there.
 |
| HC05 with Key Jumber is shorted |
Open terminal software select correct serial port
Please
note that you should select baud rate of
38400.
To
test all connections are ok or not, you just type AT and press enter
You
will get continuous OK string, don’t worry please power off your HC05 module
and reopen terminal now.
Again connect the module using terminal software and sent AT+ROLE=1
 |
| Terminal software window |
If
everything is ok, then your module become MASTER now. To check it is master or
not just power ON the device and search it using a phone.
Alternatively
power on another HC module (slave config) and Power on configure HC module, if
it is MASTER, it will automatically connect to the slave module (Check PAIR LED
status)
TIP: Power on slave module before
Master one for fast pairing
