trouble interfacing bl-521 bluetooth to rs-232 con

Forum 2005-2010 (read only) Hardware Interfacing
1

hello,

maybe somebody can give me advice:
i try to interface the arduino (pin 0, 1) with a brainboxes bluetooth to rs232 converter.

as testsoftware i use a simple loopback:

Serial.print(Serial.read())

looking with the arduino serial monitor
this results in the following:

i did the following tests:

first without bluetooth:
arduino is connected via normal usb: send <1> receive <49> etc (normal ascii response)
arduino is connected via serial cable (on pins 01 to serial port on pc): send <1> receive <1> etc.
so via usb and serial cable it s working (though i dont know why it changes the represenation)

now with bluetooth:
arduino is connected via serial cable (on pins 01) to bluetooth module, arduino serial monitor is connected via bluetooth:
send <1> receive
send <2> receive
send <3> receive and the <"PI" sign>
communication happens but i can not make any sense out of it.

if i connect the bluetooth module serial to pc and open a bluetooth serial port i can send
data correct via pure data - so the BT module works.

there seems only something wrong when its connected to the arduino board.

one thing is that the module has a command mode which would explain this starnge behaviour but it is disabled.

thank you very much for any suggestions ...

best

erich

2

Pins 0 and 1 are TTL level signals. Before attaching to an rs232 interface you must convert the signal to rs232, which involves changing the voltage levels and inverting the signal. A TTL logic 0 is ~10V rs232, and a TTL logic 1 is -10V rs232. (I think the actual ranges for RS232C is somewhere around 9 to 15 and -9 to -15.)

If your bluetooth device expects a true rs232 interface, this is probably your problem. To make it a true rs232 interface you'll need to use something like a MAX232 between the arduino and the bluetooth device.

There are some rs232 variants (RS232F, IIRC) that use TTL voltages but the signal is still inverted. This means you could use a simple TTL inverter (7404) to get the appropriate signal.

-j

3

hello,

thx for the suggestions - u were right. as the device is powerd with +5V i made the wrong assumption and thought it is working within TTL levels- but it is not.

best

erich