Overview

The idea behind this project was to make use of the new bluetooth modules that allow a serial connection to be created to an external device.
 

note: not all modules are the same check the specifications of the module you intend to purchase before you buy.  

These modules run on 3.3V and as such have logic levels operating at this potential.

In order to use one of these modules in essence we have two problems, firstly RS232 utilize     +/- 12V signals to relay data between devices and secondary the requirements of the module itself need to be met.

A common device for interfacing with RS232 is the popular MAX232 integrated circuit, the MAX232 device is designed to interface RS232 communications potentials (+/- 12V) to TTL potentials (+5V/0V).

A MAX3232 device is also available that is specifically designed to interface between RS232 and 3.3V logic, but in this instance I have opted for the MAX232 device (I have a reasonable stock of these) as with a little extra circuitry these can also be used with 3.3V logic.

Circuit

RS232 to TTL logic board

As outlined above the RS232 converter is based around the MAX232 device, the circuit includes LED drivers to indicate Tx and Rx data and a 100mA +5V regulator. Data Out is supplied at +5V and +3.3V logic levels via a potential divider.Here the Data In input will work for +5V & +3.3V logic levels, as according to the data sheets available online a standard production MAX232 has an true state input logic threshold of approximately 2V.

The circuits stripboard layout was then laid down on paper,

and constructed for testing.

BT Module support board

The BT module support board is in reality just a power supply and configuration link to allow the modules parameters to be changed.

 Once again the design was planned out for constructed on stripboard,

 then assembled.

 Finally the two boards were connected together, tested and transferred into a suitable case.

Creating a test connection from a mobile phone to a PC. 

The only thing remaining is to test the unit from end to end, for this I used "Bluetooth Terminal" on an android device and "RealTerm" on the PC (see links below). Once the bluetooth module was paired with the phone it was possible to send data to and from the PC to the phone.

Links:

http://realterm.sourceforge.net/

https://play.google.com/store/apps/details?id=Qwerty.BluetoothTerminal&hl=en