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I just got this awesome Bluetooth module in the mail. I connected power and UART pins, and tied pin 34 to +3.3v with a 1k resistor (that puts the module into AT command mode rather than pass-through bluetooth mode).

So the first thing I notice is that it's sending "ERROR:(0)" repeatedly at about 15 messages per second. But if I send a character, it stops. If I have stopped it, then I can send an AT command such as "AT" followed by enter. The module proceeds to then send "OK" repeatedly at 15 messages per second.

I'm going through all the supported AT commands, and each one works, but it continuously repeats itself until I press the any key.

I tried connecting the CTS/RTS pins but it acts the same way as when I just use the UART pins alone.

I'm connected to my PC via USB FTDI UART cable that basically gives me a serial port on my PC (/dev/ttyUSB0) and a uart header on the other end, which I have connected the module to.

When I send the AT commands, I am getting valid responses, it's just that I have to press a key to stop it from sending its response over and over, and that key gets thrown away.

Seems really weird, but I bet there's a good explanation out there?

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  • \$\begingroup\$ Check your line ending, are you sending CR, LF, or CR+LF? And what does the device expect? \$\endgroup\$ – Ben Voigt Mar 31 '13 at 5:39
  • \$\begingroup\$ I have exactly the same issue ... researching and reading. \$\endgroup\$ – Kolban May 22 '16 at 17:09
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It sounds like you've connected TX and RX together.

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  • \$\begingroup\$ Wow I never thought of that, but it's entirely possible. I'm using a wide tip soldering iron to solder to surface mount size connections, and it's possible I blobbed between TX/RX. I'll check that with an ohmmeter when I'm back in the lab tonight. \$\endgroup\$ – Brad Hein Sep 9 '10 at 12:37
  • \$\begingroup\$ TX & RX not shorted. It must be something else. \$\endgroup\$ – Brad Hein Sep 10 '10 at 10:54
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Try connecting your USB serial port to another PC to actually verify that when you send AT, it's only being sent once.My guess is your terminal emulator is sending the same sequence repeatedly.

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  • \$\begingroup\$ Good idea. I have a second USB UART adapter, so I'll connect both of them to each other and try and pass data between them. \$\endgroup\$ – Brad Hein Sep 9 '10 at 12:36
  • \$\begingroup\$ Verified the UART adapter this morning, it's rock solid with other devices and with this device when its in pass-thru mode (as opposed to AT mode). I sent a message off to their engineers to see what they say. \$\endgroup\$ – Brad Hein Sep 10 '10 at 12:02
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This is what solved this specific issue for me: (using Terminal v1.93b)

Under Transmit, set checkbox CR=CR+LF Without the linefeed char, the HC05 exhibited this behavior.

Also, make sure that in the send text box the the +CR is checked, this will append the +CR+LF every time you press send or enter.

Set baud rate to 38400, no handshaking, no parity, 1 stop bits

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If you can, make sure that it isn't resetting itself repeatedly until you send a character. It might be something like that. But check everything that everyone else suggested as well.

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You should have enabled linefeed at the end of the line in hyperterminal.

file->properties->settings->enable linefeeed.

And the baudrate should be 38400 with 1 stop and 0 parity.

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