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Tunnel – 3G gateway “Bluetooth Client” to access devices with “Bluetooth Server” 2.0 connectivity

Scenario details:

  • There’s a Bluetooth 2.0 device configured with a SPP profile (Serial Port Profile) in server mode. Right now, we have a worker who needs to go there with a Bluetooth pone to be able to read the device
  • We need to reduce worker transportation to reduce costs, so we want to install a 3G modem with Bluetooth connectivity next to the device we want to read. The goal is to make a transparent 3G Bluetooth gateway

Solution: MTX-3G-Java-BT modem + MTX-Tunnel firmware

Configuration example (config.txt file) for said scenario for each MTX-Tunnel:

COMM2_baudrate: 115200
COMM2_bitsperchar: 8
COMM2_autorts: on
COMM2_autocts: on
COMM2_stopbits: 1
COMM2_parity: none

GPRS_apn: internetestatico.movistar.es
GPRS_timeout: 0

MTX_PIN: 0000
MTX_model: MTX-3G-Java-BAT
MTX_mode: server
MTX_urc: off
MTX_IP: 30

TCP_port: 0
TCP_port2: 20011

SMS_allPhones: on
SMS_sendIP: on
SMS_ATEnabled: on
SMS_ATResponse: on

FIREWALL_enabled: off
TELNET_enabled: on
TELNET_login: user
TELNET_password: 1234
TELNET_port: 20023

BLUETOOTH_enabled: on
BLUETOOTH_pin: 1234
Serial port baud rate
Number of bits
CTS hardware flow control on
RTS hardware flow control on
1 stop bit
No parity
APN GPRS provided by the GSM operator
GPRS Login
GPRS Password
Modem is always GPRS connected
If SIM card doesn’t have PIN, leave as 0000
Modem model
We do not want GPRS gateways
URC information messages off
Connectivity chekcing IP via PING
PING time frame in minutes
3G- COM1 gateway disabled
TCP port for the 3G-Bluetooth gateway
SMS sent with commands from any cellphone
Modem will answer its IP to a missed call or SMS
Commands can be sent to the MTX via SMS
MTX will answer with an SMS to a command SMS
To connect to the modem from any IP
Modem Telnet enabled
Login for Telnet
Password for Telnet
Telnet TCP port
Bluetooth enabled
Bluetooth friendly name
Security PIN of the Bluetooth device to be read


  • To activate Bluetooth connect to MTX modem IP and to TCP port, specify 20011 in TCP_port2
  • To activate the Bluetooth Client connection with the device, the TCP socket will need to send:
    • Where AA:BB:CC:DD:EE:FF is the Bluetooth MAC of the device we want to connect to. After sending said command, we will receive the following answer via the TCP socket:
    • CALL 0
    • Everything we send via 3G to MTX modem TCP 20011 port will be forwarded to the device, where we connect to a Bluetooth device with MAC 00:12:6f:00:92:e5

To end the connection we send “+++” (without pressing ENTER) via TCP socket and then “CLOSE 0”. We’ll receive “READY”. to close the Bluetooth connectivity send “CLOSE 0”.

We will receive “NO CARRIER 0” as an answer to the command “CLOSE 0”