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Copyright © Matrix Multimedia Ltd.
Circuit Description
1.
AT Commands
Th
e GSM module uses a serial connection to transfer
commands and data to and from the microcontroller. To
do this there is a standard called AT commands which the
microcontroller uses to perform functions on the GSM.
AT commands are simply strings of serial data starting
with the characters “AT” standing for “Attention”.
Here are some of the more generic AT commands avail-
able on the GSM module.
ATD07712345678;
- dial the number specified
ATA
- answer an incoming call
ATH
- disconnect an active call
For a list of all the supported AT commands please refer
to the datasheet available from here.
http://www.telit.com/module/infopool/download.
php?id=542
2.
5V / 3.3V Operation
The GSM module requires a supply voltage of 3.8V and
I/O signal voltage of 2.8V. To allow the module to work
with 3V3 and 5V systems a voltage shifting circuit has
been fitted onto the board. Care must be taken to connect
the correct screw terminal to the correct voltage source.
Note: Powering the board with the external voltages setup
incorrectly is likely to cause irreversible damage to the
module. Please take care when wiring up the external volt-
ages to unplug your power supply and double check your
connections before plugging it back in.
3.
SIM Card socket
SIM cards used with the module must be pre-pay (“Pay
As You Go”) rather then contract based as contract based
SIM cards are normally heavily encrypted by the service
provider.
4.
Status LED
The LED on the board will flash every second when the
GSM module is trying to establish communications
with the GSM network. Once the communications have
been established and a good signal is being received the
LED will flash quickly and then remain off for around 3
seconds. When the module is in a call or communicating
with the GSM network the LED will remain constantly lit.
5.
Onboard Antenna
The on-board antenna provides good signal strength even
in weaker area’s so no external antenna connection has
been provided.
