The following example is a typical configuration for an ultra low power system with GPRS communication. Let’s imagine that our scenario is in the countryside and therefore we can’t use a normal power supply (i.e. no 220v outlet). We have 3 devices with RS232 ports that are collecting data and we want to read them once a day from a central control centre.

The application’s consumption is critical, so GPRS modems must be completely switched off (2 uA consumption) and only turned on once a day for a few minutes to share information with the server. This way, the modem’s batteries will last several years. Let’s look at the entire scenario in a bit more detail.

Example scenario details:

• There are three weather stations with RS232 serial ports. They run on batteries and continuously collect meteorological parameters that they save to their internal memory. The saved meteorological data in them needs to be read once a day via GPRS, but without compromising the system’s power consumption i.e. a minimum consumption is required by the GPRS modem connected to the meteorological station.

• For this reason, the modems must remain in ultra low power mode (2 uAmperios) for 24 hours and only wake up for a few minutes.

• Every 24 hours the modems must wake up, connect to the GPRS and connect to a remote server that we have in the office with the IP address 200.201.202.203 which the TCP port 20010 is listening for.

• As soon as the MTXTunnel is connected to the remote server, the first thing you have to do is identify MTXTunnel (the server has to know which of the 3 MTXTunnels is connected at any given time). To do this each modem has to send a different ID to connect e.g. “Device1″, “Device2″ and “Device3″.  Once the ID is sent, a transparent GPRS-RS232 tunnel will be established between the server in the central offices and the weather station connected to MTXTunnel. This is so that the central server can read data from the weather station as if it were connected with an RS232 serial cable.

• A tunnel will be established for 2 minutes i.e. if 2 minutes pass without any GPRS traffic, the MTXTunnel will go into ULP mode (unltra low power) and it won’t wake up for 24 hours.

Proposed solution with MTX-65ULP + MTXTunnel

MTX-65ULP + MTXTunnel configuration file for the proposed solution above.

You have to enter this into the modem’s configuration file to be able to run the application as described in the scenario:

COMM_baudrate: 9600 Serial port baud
COMM_bitsperchar: 8 8 data bits
COMM_autocts: off CTS hardware flow control deactivated
COMM_autorts: off RTS hardware flow control deactivated
COMM_stopbits: 1 1 stop bit
COMM_parity: none No parity
   
GPRS_apn: movistar.es GPRS APN provided by GSM operator
GPRS_login: MOVISTAR GPRS Login provided by GSM operator
GPRS_password: MOVISTAR GPRS Password provided by GSM operator
GPRS_timeout: 120 Modem is permanently connected to GPRS
   
MTX_PIN: 0000 If the SIM card doesn’t have a PIN, leave it as 0000
MTX_model: MTX65ULP Modem’s model
MTX_mode: client The modem is configured as a TCP client
MTX_IDClient: equipoX MTXTunnel identifier, the X must be different for each modem
MTX_urc: off We don’t need URC information messages
   
TCP_IP: oficina.midominio.com PC server’s IP (DNS) which it connects to
TCP_port: 20010 PC server’s TCP port which it connects to
   
ULP_sleepMode: mnutes Indicates that the modem will wake up every X minutes
ULP_rtc: on The modem will use the RTC to wake up every X minutes
ULP_minutes: 1440 The modem will wake up every 1440 minutes = 24 hours
ULP_mode: gprs Telemetries will be sent via GPRS (not SMS)

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