HC-05 bluetooth master fails to link with some slave devices

Hi everyone,
I intend to build a remote controle using HC-05 (ZS-040) bluetooth module. I need it to act as master in bluetooth connection, and using it I have problem to connect to certain slave devices - I highlight that only to some of them, to the others no problem. Also no problem when HC-05 acts as slave, see following table:

second device HC-05 as master HC-05 as slave Sony Ericsson K550i as master
notebook (Ubuntu 14.04) with Foxcon Broadcom BCM20702 bluetooth chip FAIL OK OK
bluetooth dongle Conwise CW6622, MBT-503-03 FAIL OK OK
bluetooth dongle Asus BT400 FAIL OK FAIL
mobile phone Sony Ericsson K550i OK OK -
bluetooth module ConnectBlue OBS410i OK not tested OK

On HC-05 in AT mode I first pair the devices, it is all right, and then issue the LINK command, which fails. The communication with HC-05 looks like:

AT+ROLE=1
OK
AT+PAIR=1234,56,abcdef,20
OK
AT+LINK=1234,56,abcdef
FAIL

On notebook (Ubuntu 14.04) I run bluetooth daemon in verbose mode by commad

sudo bluetoothd -nd

and get error log like:

bluetoothd[6803]: plugins/mgmtops.c:mgmt_event() cond 1
bluetoothd[6803]: plugins/mgmtops.c:mgmt_event() Received 36 bytes from management socket
bluetoothd[6803]: plugins/mgmtops.c:mgmt_device_connected() hci0 device 98:D3:31:90:5F:A4 connected eir_len 17
bluetoothd[6803]: src/adapter.c:adapter_get_device() 98:D3:31:90:5F:A4
bluetoothd[6803]: plugins/mgmtops.c:mgmt_event() cond 1
bluetoothd[6803]: plugins/mgmtops.c:mgmt_event() Received 14 bytes from management socket
bluetoothd[6803]: plugins/mgmtops.c:mgmt_device_disconnected() hci0 device 98:D3:31:90:5F:A4 disconnected
bluetoothd[6803]: src/event.c:btd_event_disconn_complete() 
bluetoothd[6803]: src/adapter.c:adapter_remove_connection()

I cannot see there any error, it looks like HC-05 disconnects itself, but only on computer. The question I am not able to answer is: why? And how to debug, what happens on HC-05?


Comments under line:

  • Asus BT400 dongle seems crappy, not working for any device
  • I tested both dongles both on ubuntu and windows - with exactly the same result
  • I played also with AT+SENM command - security and encryption on HC-05, with no result