# UART no reply from BTM511 Bluetooth module

I am trying to connect a Bluetooth module (BTM511) with my Arduino.

In order to see that I can actually communicate with the module, I first try to just send AT<cr> to the module, where I should get an <cr,lf>OK<cr,lf> from the module, using the signal generation function of my Scanalogic2 analyzer. Pin 1 (in output mode) of the analyzer is connected to the module's RX, pin 4 (in input mode) connected to the module's TX.

Now, when I send the AT command, I never get a reply back. The TX line stays LOW all the time. I DO get it work when I start the analyzer, setting it to wait sending for a logic change on Pin 4 and then, while it is waiting, connecting Pin 3 (which is in input mode) to the TX as well. Then somehow the TX line goes HIGH, and the module reports back with the OK signal.

I hope the situation is clear. Could anybody explain to me what might be happening here, and what I am doing wrong?

• Have you got the right baud rate etc? Have you got the TX/RX the right way round? – pjc50 Jul 31 '12 at 13:44
• It sounds like something you are doing wrong with the LA - can you post an image of exactly what you are sending? – Oli Glaser Jul 31 '12 at 14:56
• baudrate is 9600 8n1, the default for the Bluetooth module. I made a screen shot of when both pin 3 and 4 are connected ( imageshack.us/photo/my-images/820/sendgood.png) and when only one input pin is connected img338.imageshack.us/img338/6272/sendbad.png. The signal I sent is also shown there. – Arvest Jul 31 '12 at 15:13
• i see that in the second screen shot it looks as if the third byte <CR> is not correct, but that was not the case when I tried it. It is indeed a 0x0D as indicated in the left pane. – Arvest Jul 31 '12 at 15:50