3G SARA Click

How does it work?

3G SARA Click is based on the SARA-U201, a 3.75G HSPA cellular module from u-blox. The SARA U-201 module can be used worldwide, where a complete list of frequencies and other relevant info about the module itself can be found in the attached SARA-U201 datasheet. This device is the main component of the Click board™, consisting of several internal blocks or sections, such as the 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 that report the antenna status, sim card status, SIM card interface lines, GPIOs, UART interface lines, USB interface lines, I2C bus lines, device control lines, and I2S bus lines.

The SARA-U201 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 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 this LDO had to be used.

Digital sections of the SARA-U201 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 6-bit 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 selects 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-U201 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-U201 module is designed as the traditional DCE device (Data Communication Equipment), offering the full UART pin count, including the hardware flow control pins. These pins are routed to the mikroBUS™ pins RTS and CTS and can be used in the MCU software if the hardware flow control is needed. The ringing indicator is routed to the mikroBUS™ RI pin.

The network connection status pin is routed to both the mikroBUS™ STAT pin through the level shifter and the yellow LED used to indicate the network connection status visually. The transmitting status is indicated by the red TX LED next to the STAT LED. The network status is indicated by the STAT pin and the STAT LED by six patterns. The PWRKEY pin is routed to the mikroBUS™ PWR pin and used during the power-up sequence. A low pulse on this pin will power the device if a 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 mentioned, SARA-U201 offers the I2S interface, mainly used for digital audio. The MAX9860, a 16-bit mono audio voice CODEC IC from Analog Devices, provides the 3G SARA Click with voice communication. This IC uses the I2S and I2C interfaces to communicate with the SARA-U201 module. It is also powered with 1.8V from the LDO, so no level shifting is required. 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 also equipped with a micro USB connector. It allows the module to be powered and configured by a personal computer (PC). The u-blox company offers a software suite that can be used to configure the SARA U-201 module. The u-blox’s m-center is 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. Viewing and editing SIM directory entries, sending text messages, and communicating with the wireless module using AT commands are possible. The Micro SIM card holder on the back of the Click board™ is used to install a SIM card. This device can’t be used without a valid SIM card, which allows connection to the cellular network. Both 1.8V and 3V SIM card types are supported.

This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the PWR SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. However, the Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used, as a reference, for further development.

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 Connection Status	STAT	1	AN	PWM	16	RI	UART RI
Power ON	PWR	2	RST	INT	15	CTS	UART CTS
UART RTS	RTS	3	CS	RX	14	TX	UART TX
	NC	4	SCK	TX	13	RX	UART RX
	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

Onboard settings and indicators

3G SARA Click electrical specifications

Software Support

We provide a library for the 3G SARA Click as well as a demo application (example), developed using MIKROE compilers. The demo can run on all the main MIKROE development boards.

Package can be downloaded/installed directly from NECTO Studio Package Manager (recommended), downloaded from our LibStock™ or found on Mikroe github account.

Library Description

This library contains API for 3G SARA Click driver.

Key functions

• Power module.

• Send command.

Example Description

This example reads and processes data from 3G SARA clicks.

 void application_task ( void ) 
 { 
     c3gsara_process( ); 

     if ( send_data_cnt == 5 ) 
     { 
         c3gsara_send_command( &c3gsara, C3GSARA_ATH_COMMAND ); 
         c3gsara_process( ); 
         send_data_cnt = 0; 
     } 
     else 
     { 
         send_data_cnt++; 
     } 
 }

The full application code, and ready to use projects can be installed directly from NECTO Studio Package Manager (recommended), downloaded from our LibStock™ or found on Mikroe github account.

Other Mikroe Libraries used in the example:

• MikroSDK.Board
• MikroSDK.Log
• Click.3gSara

Additional notes and informations

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. UART terminal is available in all MIKROE compilers.

mikroSDK

This Click board™ is supported with mikroSDK – MIKROE Software Development Kit. To ensure proper operation of mikroSDK compliant Click board™ demo applications, mikroSDK should be downloaded from the LibStock and installed for the compiler you are using.

For more information about mikroSDK, visit the official page.