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tutorials:common:customization:wireless_serial_port

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Wireless Serial Port Based on Bluetooth

About this Article

Abstract

Sometimes, the serial port cable between Cubieboard and PC is annoying, because it may mess up your desktop. In this tutorial, two similar approaches are presented to guide you to get rid of the annoying cable. Serial-bluetooth module is quite common and cheap these days, and it is really a good choise to make a wirless serial port connection to PC.

Method one: ttyS0 directed to serial-bluetooth module

Prerequisite

Hardware

  • Cubieboard side: A serial-bluetooth module, to be attached to Cubieboard's TTL serial port. Notice that, this module should be 3.3v powered, because Cubieboard's TTL VCC is 3.3v.

  • PC side: Another serial-bluetooth module combined with a TTL-to-USB serial module(5.0v VCC), to be plugged into PC's USB port. If your PC has a built-in bluetooth, these two modules could be omitted, but you have to create the bluetooth serial port(rfcomm port) for communicating on your own, will be discussed later of this tutorial.

  • Some connecting wires and 2.54mm connectors

Software

  • Cubieboard side: ttyS0 should be configured as an interactive console, which means the following configurations should be done
    1. /boot/uEnv.txt should add extra boot arguments like bootargs=console=ttyS0,115200
    2. /etc/inittab should add a line like T0:2345:respawn:/sbin/getty -L ttyS0 115200 vt100
  • PC side: Serial console clients like minicom or gtkterm(recommended)

Configuration & Connection

  • Both serial-bluetooth modules should be configured to baud rate at 115200, and pre-paired.
  • The 3.3v serial-bluetooth should be conected to Cubieboard's TTL serial port(aka. ttyS0 in Linux)
  • The 5.5v serial-bluetooth module combined with the TTL-to-USB module, should be plugged into the PC's USB port
  • Open gtkterm(or minicom) port /dev/ttyUSB0 with parameters 115200-8-n-1

Method two: usb serial console to serial-bluetooth module

When installed in a case, like this, Cubieboard's TTL interface would be blocked and can no longer be plugged in the TTL to USB cable. In this case, we could exploit the USB port to make wireless serial port possible. This method is a bit different from method one previously mentioned, especially on the Cubieboard's side.

Prerequisite

hardware

  • Cubieboard side: A serial-bluetooth module, combined with a TTL-to-USB serial module (5.0v VCC), to be plugged into Cubieboard's USB port.
  • PC side: The same as method one.

software

Cubieboard's kernel configuration should be done, enable below configs (press 'Y' to select)

  1. Device Drivers→USB support
  2. USB Serial Converter support
  3. USB serial console device
  4. The USB serial driver corresponding to the TTL-to-USB serial module, USB Prolific 2303 Single Port Serial Driver in my case.

:!: Do remember, all above features should be compiled into kernel instead of modules.

Like configurations mentioned in method one, the follwing alteration should be done.

  • /boot/uEnv.txt should add extra boot arguments like bootargs=console=ttyUSB0,115200
  • /etc/inittab should add a line like T0:2345:respawn:/sbin/getty -L ttyUSB0 115200 vt100

Connection

Both Cubieboard and PC 's USB port will be used for connection.

For those PC has built-in bluetooth device

If your PC has a built-in bluetooth device, the serial-bluetooth module and TTL-to-USB serial module won't be necessary anymore. Most OS can simulate the built-in bluetooth as a serial port(a COM port for Windows, or a rfcomm for Linux). Assuming your OS is Linux, the configurations are described below.

Firstly, install the necessary packages.

$ sudo apt-get install bluez

Secondly, create /dev/bluetooth/rfcomm.conf, input these lines

#
# RFCOMM configuration file.
#

rfcomm0 {
#	# Automatically bind the device at startup
	bind no;
#
#	# Address of the bluetooth device attached to cubieboard
        # This address could be achieved by "hcitool scan"
	device 00:06:69:00:0B:D3;
#
#	# RFCOMM channel for the connection
	channel	1;
#
#	# Description of the connection
	comment "Cubieboard bluetooth device";
}

Thirdly, start the bluetooth service

$ sudo service bluetooth start

Then, bind the target bluetooth to a serial port

$ sudo rfcomm bind /dev/rfcomm0

At last, you can open this port as usual serial ports

$ minicom -D /dev/rfcomm0

Conclusion

  • method one is simpler, but the TTL port is the only choice for connection.
  • method two needs more hardware, and the boot message such as U-Boot message could never show up, because the USB serial console won't work until the kernel boots up. The advantage is USB connection is much easier and could be expanded by USB hubs.

References

tutorials/common/customization/wireless_serial_port.1383955765.txt.gz · Last modified: 2013/12/23 14:50 (external edit)