03
Aug
11

Bluetooth TTL module and Murphy

I bought a new Bluetooth Serial TTL module at eBay for a project of mine, which I will probably documenting here.

It is from MDFLY, as can be seen in the pictures below. The model is RF-BT0417CB.

Since at the time I had not yet received my Arduino 2009, a friend of mine suggested I test it with his Bus Pirate v3.5(BP for short).

He had bought one but never really used it, so there were the two of us, trying to get the BP to work. It is accessed through serial through USB, so to talk to it we discovered that screen does emulate serial connections!

screen /dev/ttyUSB0 115200

(BAUD rate does not need to be 115200, could be any other probably, and device may not be /dev/ttyUSB0… check your dmesg)

Obs.: screen is a Linux program, not Windows. Deal with it or install Cygwin. ‘Ctrl+a, k, y’ kills the screen so you can close it if you need to(probably will).

After connecting, screen is black. Hit ENTER to have ‘HiZ>’ appear. Now we need to set the mode that the BP will operate, since it has many available features.

HiZ>m
1. HiZ
2. 1-WIRE
3. UART
4. I2C
5. SPI
6. 2WIRE
7. 3WIRE
8. LCD
9. DIO
x. exit(without change)

(1)>3
Set serial port speed: (bps)
1. 300
2. 1200
3. 2400
4. 4800
5. 9600
6. 19200
7. 38400
8. 57600
9. 115200
10. BRG raw value

(1)>5
Data bits and parity:
1. 8, NONE *default
2. 8, EVEN
3. 8, ODD
4. 9, NONE
(1)>
Stop bits:
1. 1 *default
2. 2
(1)>
Receive polarity:
1. Idle 1 *default
2. Idle 0
(1)>
Select output type:
1. Open drain (H=Hi-Z, L=GND)
2. Normal (H=3.3V, L=GND)
(1)>2
Ready
UART>

Explained:
UART is so the BP can comunicate through serial, 9600 is normally the default speed, most of the rest are default options, and I prefer to use the ‘Normal’ output type because my Bluetooth module is TTL.

You will also need to connect the pins of the BP to the module:

BP -> MODULE
GND->GND
+5V->+5V
MOSI->RX
MISO->TX

Now we need to set the BP to power the module:

UART>W
Power supplies ON

The modules LED should begin to blink. If it stays on steadily it means that the module is connected through Bluetooth to another device. If it is off.. recheck the previous steps.

UART>{
UART LIVE DISPLAY, } TO STOP

This sets the BP to listen to incoming serial data. If there is a stream of data that should not be, it usually means that the TX is not connected properly to the MISO pin or that the module is turned off.

To test the communication with the device, send “AT” to it with:

WRITE: “AT”
UART>
READ: 0x4F
UART>
READ: 0x4B

The AT command should return “OK”(O=0x4F, K=0x4B).
If this doesn’t happen, recheck the TX->MISO connection or the BAUD rate for the module may be wrong. Try setting the BAUD rate to other values by redoing the mode setup.
Note: the ‘b’ command for the BP sets the BAUD rate for the pc side communication, not the module side.

Now comes the ‘problem’. Somewhere I read that the command to set/see the BAUD rate of the device was “AT+BAUD1”. This actually sets the BAUD rate to 1200. Great!. The recommended setting is “AT+BAUD4”, which will set it to 9600.

Second problem. The Bluetooth module is kind of picky when sending a ‘complex’ command. “AT” should work at almost any place, “AT+…” will probably not.
As I showed above, sending “AT” will return “OK” but in hex, not as chars. When using “AT+BAUD4” or “AT+VERSION”(check the version), the hex numbers representing the string will be shown, and not characters, which is a pain.
Also, when sending and receiving data through other devices, the data will be shown as hex, which normally isn’t very practical.

You can run the BP in Macro mode.

UART>(0)
0.Macro menu
1.Transparent bridge
2. Live monitor
3.Bridge with flow control

2 and 3 can be used on to read. When pressing a key the exit the mode. So pretty useless for normal applications.
The ‘Transparent bridge’ mode connects you ‘directly’ to the module. In this mode you receive the characters normally, not in hex, but everything you write does not appear for you AND every char you send, is sent as you type, not after you press enter. So while “A” and then “T” will work and you will receive “OK” as an answer; “A”, “T”, “+”, and then the command will not work since apparently it takes to long for each char to reach the module, so the command is discarded and you don’t even receive the “OK” for the “AT” part.


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