New Model 340 GSM/GPRS Modem: More features for Less

The long holidays gave me the opportunity to play around with our new SIMCOM based GSM modem Model 340 for the first time (and write this blog). The Model 340 GSM Modem has undergone and passed our usual verification tests. Production is already underway, and barring unforeseen events, limited quantities will be available for sale starting this January 2010. The main purpose of this blog is to describe its new features and  functional differences with our previous BenQ M23 based model, to allow current M23 users to migrate to this new modem with ease.

e-Gizmo Model 340 is based on SIMCOM 340DZ GSM/GPRS module. This new GSM modem kit will replace our now obsolete BenQ M23 based model. The Model 340 is already GPRS capable, yet costs much less than the outgoing M23 based model.

  
HARDWARE INTERFACE

Visual Indicators

The new MODEM is equipped with LED visual status indicators.  The power indicator (D3 -Green LED) indicates that 5V power is available and active, the status indicator (D1 – orange) will illuminate to indicate the GSM Modem is in power ON state, and finally, the network indicator (D2- RED ) flashes briefly once every three seconds to indicate a successful connection with a GSM network service provider. The network indicator flashes at a different rate according to network usage. Complete description can be found in the Hardware Design Manual of the SIM340DZ module.

Model 340 is equipped with visual indicators that will tell the user what the GSM/GPRS modem is doing in just one quick glance. I personally find this feature very desirable. Like the M23 model it replaces, the 340 has an on board push button switch that can be used to manually power up the modem.

Serial Interface

Our now obsolete BenQ model has on board RS-232 converter that most users find of little value. The reason is user applications usually involve interfacing the GSM modem with a microcontroller UART that operates at TTL level. Hence, in this new model, we decided not to include an on board RS-232 converter resulting in an even lower cost.

For new users who may want to try out to learn the feature of the GSM modem using a PC, a separate general purpose TTL to RS-232 converter kit is available suited for this purpose. After you finished your familiarization, you may then use the RS-232 converter kit for other useful purpose (e.g. Aside from its usual role as a bridge between your microcontroller TTL UART and PC RS-232 COM port, the converter kit can be used as well as a Zilog Encore programming dongle).

Other I/O Interface

The I/O connector terminals are arranged such that I/O functions that are more likely to be used are grouped together into a single connector set JP1. The remaining I/Os are grouped together according to their functions.

All remaining, albeit seldom used, I/O ports are all accessible to users via a 3 set of header connector pads. The user must solder the appropriate header pin connectors to connect to and use these functions. These functions includes the voice circuit (microphone and receiver),  Real Time Clock RTC back up, battery charging, and display interface.


FIRMWARE FEATURES

Power ON sequence

BenQ module requires its PWR-ON pin to be pulled low at least 100mS  long to power it up. The new SIMCOM model requires at least 2000mS. The modem I have in hand turned ON with a 1300mS pulse, but it is better to keep the 2000mS recommended by the manufacturer.

AT Command Set

This device conforms to standard AT command set as defined by V.25TER, GSM07.07, GSM07.05. The BenQ M23 also conforms with this standard, this means standard AT commands (not the proprietary subset) written for BenQ should also run with no or little modification with the new Model 340 GSM Modem. For instance, the send text command AT+CMGS of BenQ M23 works exactly the same as with the Model 340. Proprietary commands like the AT$SRN of BenQ is not recognized by the Model 340.

BenQ and Model 340 GSM modem may respond to identical AT commands quite differently though. An example of this would be the difference in response between the two when the Read SMS command AT+CMGR is invoked pointing to an empty message storage. BenQ will respond with and error, while 340 will simply indicate an “OK”. If there is a message in the storage, the response will be identical. Hence, if you are migrating from our BenQ M23 based to SIMCOM 340DZ based modem, you should see to it that these differences are taken cared of.

GPRS  functions included

GPRS functions TCP/IP stack allow your GSM Modem to connect with the internet network. Through these functions, you can remotely access and transfer large amount of data to and from your GSM/GPRS connected devices using your PC or other internet enabled devices using the internet. This opens up a lot of new possibilities and features that you can incorporate in your GSM/GPRS modem based design.

Our previous M23 based modem comes in two variation: the M23A has just the GSM functions, while the M23 comes with both the GSM and GPRS functions. The later is priced a bit higher than the former because of the additional GPRS function.

In contrast, both the GSM and GPRS functions are already built-in in the new Model 340 with no additional cost. The new Model 340 GSM/GPRS Modem will as a matter of fact cost significantly less compared to the M23 GSM only model.

The differences just described is far from complete, yet what was discussed should be enough for M23 users to get started working with the new Model 340 and perform some useful functions quickly.

An external 5V power source is supplied via a DC jack. This voltage is lowered to the desired 340DZ operating voltage by an on board LDO voltage regulator. A resettable fuse will protect the GSM Modem in case a power supply polarized the wrong way is used to power the device.

We tests our engineering prototype using handmade PCBs before sending the final PCB layout for outside fabrication. This allows us to find problems (if there is any) and apply necessary fixes to ensure the final product will