3G SARA click is a versatile cellular network communication solution, featuring the compact 3.75G UMTS/HSPA SARA U-201 modem from u-blox. This module includes a full set of options for the cellular networking and communication, such as the network indication, full embedded TCP/UDP stack, HTTP and HTTPS transfer protocols, IPv4/IPv6 dual-stack support, antenna detection, jamming signal detection, and more. 3G SARA click also features the HSPA data-rates of 7.2 Mb/s (downlink) and 5.76 Mb/s (uplink), as well as the ability to maintain the voice call during the data transfer (3G). Onboard 16bit audio CODEC IC adds high-quality voice communication capability.

The SARA U-201 module is fully qualified and certified solution, that simplifies the design and cuts time to market. It is perfectly suited for a wide range of M2M applications, such as mobile Internet terminals, automatic meter reading (AMR), remote monitoring automation and control (RMAC), surveillance and security, road pricing, asset tracking, fleet management, anti-theft systems, point of sales (PoS) terminals, and similar applications which rely on a cellular network connection.

How does it work?

As already mentioned, 3G SARA click is equipped with the compact 3.75G UMTS/HSPA SARA U-201 modem, from u-blox. The SARA U-201 module can be used worldwide. A complete list of frequencies, along with other relevant info about the module itself can be found in the SARA U-201 datasheet. This device is the main component of the click board and it consists of a number of internal blocks or sections, such as antenna switching section, RF transceiver section, memory, power management, and most importantly - the cellular baseband processor. This section contains the logic necessary for managing the other sections and provides the interface to the host MCU. This interface consists of several lines used to report the antenna status, sim card status, SIM card interface lines, a number of GPIOs, UART interface lines, USB interface lines, I2C bus lines, device control lines, and I2S bus lines. These lines are routed to the respective elements of the click board.

The SARA U-201 module has to be powered by a clean and stable power supply. The voltage needed for the module to work properly is about 4V and it is derived from the 5V mikroBUS™ rail, through the MCP1826, a 1A low drop output (LDO) regulator from Microchip. Although the SARA U-201 is a low power device, the cellular network modules, in general, are notorious for their high power consumption, so the 1A LDO had to be used.

Digital sections of the SARA U-201 are internally supplied by 1.8V, so it is necessary to condition the communication bus lines which connect the host MCU with the module. For this reason, another small LDO is used, providing a needed reference voltage for one side of the TXB0106, a 6bit bidirectional level shifting and voltage translator with automatic direction sensing, from Texas Instruments. The reference voltage for the other side of the level shifter is taken from the onboard SMD jumper, labeled as PWR SEL. This jumper is used to select between 3.3V and 5V from the mikroBUS™, depending on the used MCU type and its logic voltage level requirements.

The UART bus of the SARA U-201 module is connected to one side of the level shifter, while the other side (shifted) is connected to the respective mikroBUS™ UART pins. However, the  SARA U-201 module is designed as the traditional DCE device (Data Communication Equipment) offering the full UART pin count, including the hardware flow control pins (CTS, RTS). These pins are routed to the mikroBUS™ CS (RTS) and the INT pin (CTS) and can be used in the MCU software if the hardware flow control is needed. The RI pin is the ringing indicator, and it is routed to the mikroBUS™ PWM pin.

The STAT pin is used to signalize the network connection status. This pin is routed both to the mikroBUS™ AN pin through the level shifter, and the yellow LED used to visually indicate the status of the network connection. The transmitting status is indicated by the red TX LED, next to the STAT LED. The network status is indicated by the STAT pin (also LED), using the following pattern:

• Continuous Low: if no service (no network coverage or not registered)
• Cyclically High for 100 ms, Low for 2 s: if registered home 2G network
• Cyclically High for 50 ms, Low for 50 ms, High for 50 ms, Low for 2 s: if registered home 3G network
• Cyclically High for 100 ms, Low for 100 ms, High for 100 ms, Low for 2 s: if registered visitor 2G network (roaming)
• Cyclically High for 50 ms, Low for 50 ms, High for 50 ms, Low for 100 ms: if registered visitor 3G network (roaming)
• Continuous High: if voice or data 2G/3G call enabled

The PWRKEY pin is routed to the mikroBUS™ RST pin, and it is used during the power-up sequence. A low pulse on this pin will power up the device if the valid supply voltage is provided. To properly detach from the network and store the working parameters in its non-volatile memory, the module should be safely powered off either by issuing the AT+CPWROFF command or by a low pulse on the PWRKEY pin for at least 1 second, before disconnecting the power source.

As already mentioned, SARA U-201 offers the I2S interface, mainly used for digital audio. The MAX9860, a 16bit mono audio voice CODEC IC from Maxim Integrated, provides the 3G SARA click board with the voice communication. This IC uses the I2S and I2C interfaces to communicate with the SARA U-201 module. It is also powered with 1.8V from the LDO, so no level shifting is required in this case. This IC provides a clean and audible analog interface for connecting the headset, with one audio output channel and one microphone input channel. The headset can be connected via the onboard 3.5mm audio jack.

SARA 3G click is equipped with the micro USB connector. It allows the module to be powered and configured by a personal computer (PC). u-blox company offers a software suite that can be used to configure the SARA U-201 module.

The Micro SIM card holder on the back of the click board™ is used to install a SIM card. This device can not be used without the valid SIM card, which allows connection to the cellular network. Both 1.8V and 3V SIM card types are supported.

Free u-blox software

u-blox offers m-center, a free evaluation software for all their cellular modules. It has an easy-to-use graphical interface and can be used to configure the module and save changes to the EPROM. It is possible to view and edit SIM directory entries, send text messages, and communicate with the wireless module using AT commands.

Additional information

More information about 2G/3G/4G networks, in general, can be found here.

Additional information about how to use AT commands and parsers to configure and use the module can be found here.

Specifications

Pinout diagram

This table shows how the pinout on 3G SARA click corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

Notes	Pin					Pin	Notes
Network Status	STAT	1	AN	PWM	16	RI	Incoming ring detection
PowerKey	PWR	2	RST	INT	15	CTS	UART Clear To Send
UART Request to Send	RTS	3	CS	RX	14	TX	UART Data Transmit
	NC	4	SCK	TX	13	RX	UART Data Receive
	NC	5	MISO	SCL	12	NC
	NC	6	MOSI	SDA	11	NC
Power supply	+3.3V	7	3.3V	5V	10	+5V	Power supply
Ground	GND	8	GND	GND	9	GND	Ground

Software support

We provide the library for 3G SARA click on our LibStock page, as well as the demo application (example), developed using MikroElektronika compilers and mikroSDK. The provided click library is mikroSDK standard compliant. The demo application can run on all the main MikroElektronika development boards.

Library Description

The library carries a generic command parser adopted for AT command based modules.
Generic parser.

Key functions:

• c3gsara_cmdSingle - Sends the provided command to the module.
• c3gsara_setHandler - Handler assignation to the provided command.
• c3gsara_modulePower - Turn the module on.

Examples Description

Example demo application waits for the call. After the call is received the parser will get hangup call.

This code snippet shows how a generic parser should be properly initialized. Before initialization module must be turned on, and hardware flow control should be also added. 

Commands:

• The first command negotiates the baud rate with the module.
• The second command turns the echo off.
• The third command enables hardware flow control - necessary in case of UART polling.
• The fourth command sets the setup default message format.

// MODULE POWER ON
 c3gsara_hfcEnable( true );
 c3gsara_modulePower( true );

// MODULE INIT
 c3gsara_cmdSingle( "AT" );
 c3gsara_cmdSingle( "ATE0" );
 c3gsara_cmdSingle( "AT+IFC=2,2" );
 c3gsara_cmdSingle( "AT+CMGF=1" );

Along with the demo application, timer initialization functions are provided. Note that timer is configured according to default development system and MCUs, changing the system or MCU may require an update of timer init and timer ISR functions.

The full application code, and ready to use projects can be found on our LibStock page.

Other mikroE Libraries used in the example:

• String
• Conversion

Additional notes and information

Depending on the development board you are using, you may need USB UART click,  USB UART 2 click or  RS232 click to connect to your PC, for development systems with no UART to USB interface available on the board. The terminal available in all MikroElektronika compilers, or any other terminal application of your choice, can be used to read the message.

mikroSDK

This click board is supported by the mikroSDK - MikroElektronika Software Development Kit. To ensure proper operation of mikroSDK compliant click board demo applications, the mikroSDK should be downloaded from the LibStock and installed for the compiler you are using.

For more information about mikroSDK, visit the official page.