GSM Sim900A with Arduino Complete Guide with GSM based Projects Examples

30,332

Table of Contents

GSM Sim900A Description:

GSM Sim900A– the GSM SIM900A by the SIMCom is designed for global market, SIM900A is a dual-band GSM/GPRS engine that works on frequencies EGSM 900MHz and DCS 1800MHz. SIM900A features GPRS multi-slot class 10/ class 8 (optional) and supports the GPRS coding schemes CS-1, CS-2, CS-3 and CS-4.

With a tiny configuration of 24mm x 24mm x 3mm, SIM900A can meet almost all the space requirements in your applications, such as M2M, smartphone, PDA, and other mobile devices.

The physical interface to the mobile application is a 68-pin SMT pad, which provides all hardware interfaces between the module and customers’ boards.

The SIM900A is designed with power saving technique so that the current consumption is as low as 1.5mA in SLEEP mode.

The SIM900A is integrated with the TCP/IP protocol; extended TCP/IP AT commands are developed for customers to use the TCP/IP protocol easily, which is very useful for those data transfer applications.

Amazon Links:

Sim900A GSM Module:

*Disclosure: These are affiliate links. As an Amazon Associate I earn from qualifying purchases.

SIM900A key features:

GSM SIM900A Functional Diagram:

The above figure shows a functional diagram of the SIM900A and illustrates the mainly functional parts:

The GSM baseband engine
Flash and SRAM
The GSM radio frequency part
The antenna interface
The Other interfaces

GSM SIM900A Pin Description:

GSM SIM900A by the SIMCom is a 68 terminal device as shown in the pin diagram given above. I will describe the function of each pin.

Pin Number	Pin Name	Description
1	PWRKEY	Voltage input for PWRKEY. PWRKEY should be pulled low to power on or power off the system. The user should keep pressing the key for a short time when power on or power off the system because the system need margin time in order to assert the software.
2	PWRKEY_OUT	Connecting PWRKEY and PWRKEY_OUT for a short time then release also can power on or power off the module.
3	DTR	Data terminal Ready [Serial port ]
4	RI	Ring indicator [Serial port ]
5	DCD	Data carry detect [Serial port ]
6	DSR	Data Set Ready [Serial port ]
7	CTS	Clear to send [Serial port ]
8	RTS	Request to send [Serial port ]
9	TXD	Transmit data [Serial port ]
10	RXD	Receive data [Serial port ]
11	DISP _CLK	Clock for display [Display interface]
12	DISP_DATA	Display data output [Display interface]
13	DISP _D/C	Display data or command select [Display interface]
14	DISP _CS	Display Enable [Display interface]
15	VDD_EXT	2.8V output power supply
16	NRESET	External reset input
17,18,29,39,45, 46,53,54,58,59, 61,62,63,64,65	GND	Ground
19	MIC_P	Microphone Positive
20	MIC_N	Microphone Negative
21	SPK_P	Speaker Positive
22	SPK_N	Speaker Negative
23	LINEIN_R	Right Channel input [External line inputs are available to directly mix or multiplex externally generated analog signals such as polyphonic tones from an external melody IC or music generated by an FM tuner IC or module.]
24	LINEIN_L	Left Channel Input
25	ADC	General purpose analog to digital converter.
26	VRTC	Current input for RTC when the battery is not supplied for the system. Current output for backup battery when the main battery is present and the backup battery is in low voltage state.
27	DBG_TXD	Transmit pin [Serial interface for debugging and firmware upgrade ]
28	DBG_RXD	Receive pin [Serial interface for debugging and firmware upgrade ]
30	SIM_VDD	Voltage supply for SIM card
31	SIM_DATA	SIM data output
32	SIM_CLK	SIM clock
33	SIM_RST	SIM reset
34	SIM_PRESENCE	SIM detect
35	PWM1	PWM Output
36	PWM2	PWM Output
37	SDA	Serial Data [I2C]
38	SCL	Serial Clock [I2C]
40,41,42,43,44 & 47,48,49,50,51	KBR0 to KBR4 & KBC4 to KBC0	Keypad interface [ROWS & COLUMNS]
52	NETLIGHT	Indicate net status
55,56,57	VBAT	Three VBAT pins are dedicated to connect the supply voltage. The power supply of SIM900A has to be a single voltage source of VBAT= 3.4V to 4.5V. It must be able to provide sufficient current in a transmit burst which typically rises to 2A.
60	RF_ANT	Antenna connection
66	STATUS	Indicate working status
67	GPIO 11	General Purpose Input/output
68	GPIO 12	General Purpose Input/output

GSM SIM900A Applications

Cellular Communication
Home Automations
Security based projects
Sensors monitoring
Robotics
Mobile Phone Accessories
Servers
Computer Peripherals
Automobile
USB Dongles

How to use the SIM900A:

It’s seems quite impossible for a beginner to do all the soldering, I will never do this, in fact I don’t have to do this, because readymade modules are already available in the market.

GSM Sim900A Module:

This is the GSM Sim900A mini Module. The first thing that you will notice about this GSM module is that, it has no onboard voltage regulator, so be very careful while applying the voltage; Because voltages greater than 5 volts can easily damage this module. Ideal voltage for this GSM module is 4.7v but you can easily power up this GSM Sim900A module using a 5v adaptor. if you don’t have a 5v adaptor then you can make your power supply using lm317t adjustable variable voltage regulator, I have a very detailed tutorial on lm317t explaining everything.

There are a few things that I really like about the GSM sim900A module which are

This is the cheapest GSM module available on the Market.
Another cool thing is, it can be easily interfaced with 5V supported controller boards like Arduino Uno, Arduino mega, Arduino Nano etc and also with 3.3v controller boards like Nodemcu ESP8266 Wifi Module and ESP32 etc. The GSM Sim900A module interfacing with Nodemcu ESP8266 and ESP32 will be explained in one of my future articles.

GSM Sim900A specifications:

GSM Sim900A Power Supply:

As I said earlier the GSM Sim900A Module has no onboard voltage regulator. Although it has a power supply pin which can be connected with the Arduino’s 5 volts. When no sensors are connected with the Arduino then you can Run this GSM module without any problem. But the time you start connecting different sensors with the Arduino, then Arduino cannot provide enough current to the Sim900A Module due to which the Arduino starts resetting.

So, my recommendation is use an external regulated 5v power supply.

GSM Sim900A pin configuration:

The white connector labeled with 4.7 – 5V, This is where we connect the external 5volt regulated power supply. It has a total of 9 male headers. The three male headers on the right side are not connected.

Pin number 1 is the VCC which can be connected with the Arduino’s 5volts. In my case as I will power up this module using the external power supply so I will leave this pin unconnected.
Pin number 2 is the ground, which will be connected with the Arduino’s ground.
Pin number 3 is the 5v TXD,
Pin number 4 is the 5v RXD,
Pin number 5 is the 3.3v TXD, and
Pin number 6 is the 3.3v RXD.

GSM Sim900A AT commands:

TO CHECK THE MODEM:

TO CHANGE SMS SENDING MODE:

AT+CMGF=1

TO SEND NEW SMS:

AT+CMGS=”MOBILE NO.”

<MESSAGE

{CTRL+Z}

PREFERRED SMS MESSAGE STORAGE:

AT+CPMS=?

+CPMS: (“SM”),(“SM”),(“SM”)

AT+CPMS?

+CPMS: “SM”,19,30,”SM”,19,30,”SM”,19,30

TO MAKE A VOICE CALL:

ATD923339348223;

TO REDIAL LAST NO:

ATDL

TO RECEIVE INCOMING CALL:

ATA

TO HANGUP OR DISCONNECT A CALL:

ATH

OPERATOR SELECTION:

AT+COPS=?

AT+COPS?

+COPS: 0,0,”AirTel”

TO SET A PARTICULAR BAUDRATE:

AT+IPR=? {To view the baud rate values}

AT+IPR=0 {To set the modem to autobauding mode}

READ OPERATOR NAMES.

AT+COPN=?

AT+COPN

+COPN: “472001”,”DHIMOBILE”

+COPN: “60500

+COPN: “502012”,”maxis mobile”

+COPN:

+COPN: “502013”,”TMTOUCH”

+COPN

+COPN: “502016”,”DiGi”

+COPN: “502017”,”TIMECel””

+COPN: “502019”,”CELCOM GSM”

AT+CRC SET CELLULAR RESULT CODES FOR INCOMING CALL INDICATION:

AT+CRC=?

+CRC: (0-1)

AT+CRC?

+CRC: 0

AT+CRC=1

+CRING: VOICE

GPRS COMMANDS:

Command Description

AT+CGATT ATTACH/DETACH FROM GPRS SERVICE

AT+CGDCONT DEFINE PDP CONTEXT

AT+CGQMIN QUALITY OF SERVICE PROFILE (MINIMUM ACCEPTABLE)

AT+CGQREQ QUALITY OF SERVICE PROFILE (REQUESTED)

AT+CGACT PDP CONTEXT ACTIVATE OR DEACTIVATE

AT+CGDATA ENTER DATA STATE

AT+CGPADDR SHOW PDP ADDRESS

AT+CGCLASS GPRS MOBILE STATION CLASS

AT+CGEREP CONTROL UNSOLICITED GPRS EVENT REPORTING

AT+CGREG NETWORK REGISTRATION STATUS

AT+CGSMS SELECT SERVICE FOR MO SMS MESSAGES

AT+CGCOUNT GPRS PACKET COUNTERS