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TinyGSM logo

A small Arduino library for GSM modules, that just works.

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If you like TinyGSM - give it a star, or fork it and contribute! GitHub stars GitHub forks

You can also join our chat: Gitter

Arduino Client interface support

This library is easy to integrate with lots of sketches which use Ethernet or WiFi. PubSubClient (MQTT), Blynk, HTTP Client and File Download examples are provided.


TinyGSM is tiny

The complete WebClient example for Arduino Uno (via Software Serial) takes little resources:

Sketch uses 15022 bytes (46%) of program storage space. Maximum is 32256 bytes.
Global variables use 574 bytes (28%) of dynamic memory, leaving 1474 bytes for local variables. Maximum is 2048 bytes.

Arduino GSM library uses 15868 bytes (49%) of Flash and 1113 bytes (54%) of RAM in a similar scenario. TinyGSM also pulls data gently from the modem (whenever possible), so it can operate on very little RAM. Now, you have more space for your experiments.

Supported modems

  • SIMCom SIM800 series (SIM800A, SIM800C, SIM800L, SIM800H, SIM808, SIM868)
  • SIMCom SIM900 series (SIM900A, SIM900D, SIM908, SIM968)
  • SIMCom WCDMA/HSPA/HSPA+ Modules (SIM5360, SIM5320, SIM5300E, SIM5300E/A)
  • SIMCom LTE Modules (SIM7100E, SIM7500E, SIM7500A, SIM7600C, SIM7600E)
  • SIMCom SIM7000E/A/G CAT-M1/NB-IoT Module
  • SIMCom SIM7070/SIM7080/SIM7090 CAT-M1/NB-IoT Module
  • AI-Thinker A6, A6C, A7, A20
  • ESP8266/ESP32 (AT commands interface, similar to GSM modems)
  • Digi XBee WiFi and Cellular (using XBee command mode)
  • Neoway M590
  • u-blox 2G, 3G, 4G, and LTE Cat1 Cellular Modems (many modules including LEON-G100, LISA-U2xx, SARA-G3xx, SARA-U2xx, TOBY-L2xx, LARA-R2xx, MPCI-L2xx)
  • u-blox LTE-M/NB-IoT Modems (SARA-R4xx, SARA-N4xx, but NOT SARA-N2xx)
  • Sequans Monarch LTE Cat M1/NB1 (VZM20Q)
  • Quectel BG96
  • Quectel M95
  • Quectel MC60 (alpha)

Supported boards/modules

  • Arduino MKR GSM 1400
  • GPRSbee
  • Microduino GSM
  • Adafruit FONA (Mini Cellular GSM Breakout)
  • Adafruit FONA 800/808 Shield
  • Industruino GSM
  • RAK WisLTE (alpha)
  • ... other modules, based on supported modems. Some boards require special configuration.

More modems may be supported later:

  • Quectel M10, UG95
  • SIMCom SIM7020
  • Telit GL865
  • ZTE MG2639
  • Hi-Link HLK-RM04

Watch this repo for new updates! And of course, contributions are welcome ;)


Data connections

  • TCP (HTTP, MQTT, Blynk, ...)
    • ALL modules support TCP connections
    • Most modules support multiple simultaneous connections:
      • A6/A7 - 8
      • ESP8266 - 5
      • Neoway M590 - 2
      • Quectel BG96 - 12
      • Quectel M95 - 6
      • Quectel MC60/MC60E - 6
      • Sequans Monarch - 6
      • SIM 800/900 - 5
      • SIM 5360/5320/5300/7100 - 10
      • SIM7000 - 8 possible without SSL, only 2 with
      • SIM 7070/7080/7090 - 12
      • SIM 7500/7600/7800 - 10
      • u-blox 2G/3G - 7
      • u-blox SARA R4/N4 - 7
      • Digi XBee - only 1 connection supported!
  • UDP
    • Not yet supported on any module, though it may be some day
    • Supported on:
      • SIM800, SIM7000, u-Blox, XBee cellular, ESP8266, and Sequans Monarch
      • Note: only some device models or firmware revisions have this feature (SIM8xx R14.18, A7, etc.)
    • Not yet supported on:
      • Quectel modems, SIM 5360/5320/7100, SIM 7500/7600/7800
    • Not possible on:
      • SIM900, A6/A7, Neoway M590, XBee WiFi
    • Like TCP, most modules support simultaneous connections
    • TCP and SSL connections can usually be mixed up to the total number of possible connections


  • Sending USSD requests and decoding 7,8,16-bit responses
    • Supported on:
      • All SIMCom modems, Quectel modems, most u-blox
    • Not possible on:
      • XBee, u-blox SARA R4/N4, ESP8266 (obviously)


  • Only sending SMS is supported, not receiving
    • Supported on all cellular modules

Voice Calls

  • Supported on:
    • SIM800/SIM900, SIM7600, A6/A7, Quectel modems, u-blox
  • Not yet supported on:
    • SIM7000, SIM5360/5320/7100, SIM7500/7800, VZM20Q (Monarch)
  • Not possible on:
    • XBee (any type), u-blox SARA R4/N4, Neoway M590, ESP8266 (obviously)
  • Functions:
    • Dial, hangup
    • DTMF sending


    • SIM808, SIM7000, SIM7500/7600/7800, BG96, u-blox
    • NOTE: u-blox chips do NOT have embedded GPS - this functionality only works if a secondary GPS is connected to primary cellular chip over I2C
  • GSM location service
    • SIM800, SIM7000, Quectel, u-blox


Getting Started

First Steps

  1. Using your phone: - Disable PIN code on the SIM card - Check your balance - Check that APN, User, Pass are correct and you have internet
  2. Ensure the SIM card is correctly inserted into the module
  3. Ensure that GSM antenna is firmly attached
  4. Ensure that you have a stable power supply to the module of at least 2A.
  5. Check if serial connection is working (Hardware Serial is recommended) Send an AT command using this sketch
  6. Try out the WebClient example

Writing your own code

The general flow of your code should be:

  • Define the module that you are using (choose one and only one)
    • ie, #define TINY_GSM_MODEM_SIM800
  • Included TinyGSM
    • #include <TinyGsmClient.h>
  • Create a TinyGSM modem instance
    • TinyGsm modem(SerialAT);
  • Create one or more TinyGSM client instances
    • For a single connection, use
      • TinyGsmClient client(modem); or TinyGsmClientSecure client(modem); (on supported modules)
    • For multiple connections (on supported modules) use:
      • TinyGsmClient clientX(modem, 0);, TinyGsmClient clientY(modem, 1);, etc or
      • TinyGsmClientSecure clientX(modem, 0);, TinyGsmClientSecure clientY(modem, 1);, etc
    • Secure and insecure clients can usually be mixed when using multiple connections.
    • The total number of connections possible varies by module
  • Begin your serial communication and set all your pins as required to power your module and bring it to full functionality.
    • The examples attempt to guess the module's baud rate. In working code, you should use a set baud.
  • Wait for the module to be ready (could be as much as 6s, depending on the module)
  • Initialize the modem
    • modem.init() or modem.restart()
    • restart generally takes longer than init but ensures the module doesn't have lingering connections
  • Unlock your SIM, if necessary:
    • modem.simUnlock(GSM_PIN)
  • If using WiFi, specify your SSID information:
    • modem.networkConnect(wifiSSID, wifiPass)
    • Network registration should be automatic on cellular modules
  • Wait for network registration to be successful
    • modem.waitForNetwork(600000L)
  • If using cellular, establish the GPRS or EPS data connection after your are successfully registered on the network
    • modem.gprsConnect(apn, gprsUser, gprsPass) (or simply modem.gprsConnect(apn))
    • The same command is used for both GPRS or EPS connection
    • If using a Digi brand cellular XBee, you must specify your GPRS/EPS connection information before waiting for the network. This is true ONLY for Digi cellular XBees! For all other cellular modules, use the GPRS connect function after network registration.
  • Connect the TCP or SSL client client.connect(server, port)
  • Send out your data.

If you have any issues

  1. Read the whole README (you're looking at it!), particularly the troubleshooting section below.
  2. Some boards require special configuration.
  3. Try running the Diagnostics sketch
  4. Check for highlighted topics here
  5. If you have a question, please post it in our Gitter chat

How does it work?

Many GSM modems, WiFi and radio modules can be controlled by sending AT commands over Serial. TinyGSM knows which commands to send, and how to handle AT responses, and wraps that into standard Arduino Client interface.

This library is "blocking" in all of its communication. Depending on the function, your code may be blocked for a long time waiting for the module responses. Apart from the obvious (ie, waitForNetwork()) several other functions may block your code for up to several minutes. The gprsConnect() and client.connect() functions commonly block the longest, especially in poorer service regions. The module shutdown and restart may also be quite slow.

This libary does not support any sort of "hardware" or pin level controls for the modules. If you need to turn your module on or reset it using some sort of High/Low/High pin sequence, you must write those functions yourself.

API Reference

For GPRS data streams, this library provides the standard Arduino Client interface. For additional functions, please refer to this example sketch


Ensure stable data & power connection

Most modules require as much as 2A to properly connect to the network. This is 4x what a "standard" USB will supply! Improving the power supply actually solves stability problems in many cases!

  • Read about powering your module.
  • Keep your wires as short as possible
  • Consider soldering them for a stable connection
  • Do not put your wires next to noisy signal sources (buck converters, antennas, oscillators etc.)
  • If everything else seems to be working but you are unable to connect to the network, check your power supply!

Baud rates

Most modules support some sort of "auto-bauding" feature where the module will attempt to adjust it's baud rate to match what it is receiving. TinyGSM also implements its own auto bauding function (TinyGsmAutoBaud(SerialAT, GSM_AUTOBAUD_MIN, GSM_AUTOBAUD_MAX);). While very useful when initially connecting to a module and doing tests, these should NOT be used in any sort of production code. Once you've established communication with the module, set the baud rate using the setBaud(#) function and stick with that rate.

Broken initial configuration

Sometimes (especially if you played with AT commands), your module configuration may become invalid. This may result in problems such as:

  • Can't connect to the GPRS network
  • Can't connect to the server
  • Sent/received data contains invalid bytes
  • etc.

To return module to Factory Defaults, use this sketch: File -> Examples -> TinyGSM -> tools -> FactoryReset

In some cases, you may need to set an initial APN to connect to the cellular network. Try using the gprsConnect(APN) function to set an initial APN if you are unable to register on the network. You may need set the APN again after registering. (In most cases, you should set the APN after registration.)

Failed connection or no data received

The first connection with a new SIM card, a new module, or at a new location/tower may take a LONG time - up to 15 minutes or even more, especially if the signal quality isn't excellent. If it is your first connection, you may need to adjust your wait times and possibly go to lunch while you're waiting.

If you are able to open a TCP connection but have the connection close before receiving data, try adding a keep-alive header to your request. Some modules (ie, the SIM7000 in SSL mode) will immediately throw away any un-read data when the remote server closes the connection - sometimes without even giving a notification that data arrived in the first place. When using MQTT, to keep a continuous connection you may need to reduce your keep-alive interval (PINGREQ/PINGRESP).

Diagnostics sketch

Use this sketch to help diagnose SIM card and GPRS connection issues: File -> Examples -> TinyGSM -> tools -> Diagnostics

If the diagnostics fail, uncomment this line to output some debugging comments from the library:

#define TINY_GSM_DEBUG SerialMon

In any custom code, TINY_GSM_DEBUG must be defined before including the TinyGSM library.

If you are unable to see any obvious errors in the library debugging, use StreamDebugger to copy the entire AT command sequence to the main serial port. In the diagnostics example, simply uncomment the line:


In custom code, you can add this snippit:

  #include <StreamDebugger.h>
  StreamDebugger debugger(SerialAT, SerialMon);
  TinyGsm modem(debugger);
  TinyGsm modem(SerialAT);

Web request formatting problems - "but it works with PostMan"

This library opens a TCP (or SSL) connection to a server. In the OSI model, that's layer 4 (or 5 for SSL). HTTP (GET/POST), MQTT, and most of the other functions you probably want to use live up at layer 7. This means that you need to either manually code the top layer or use another library (like HTTPClient or PubSubClient) to do it for you. Tools like PostMan also show layer 7, not layer 4/5 like TinyGSM. If you are successfully connecting to a server, but getting responses of "bad request" (or no response), the issue is probably your formatting. Here are some tips for writing layer 7 (particularly HTTP request) manually:

  • Look at the "WebClient" example
  • Make sure you are including all required headers.
    • If you are testing with PostMan, make sure you un-hide and look at the "auto-generated" headers; you'll probably be surprised by how many of them there are.
  • Use client.print("..."), or client.write(buf, #), or even client.write(String("...")), not client.write("...") to help prevent text being sent out one character at a time (typewriter style)
  • Enclose the entirety of each header or line within a single string or print statement
    • use
    client.print(String("GET ") + resource + " HTTP/1.1\r\n");
    instead of
    client.print("GET ");
    client.println(" HTTP/1.1")
  • Make sure there is one entirely blank line between the last header and the content of any POST request.
    • Add two lines to the last header client.print("....\r\n\r\n") or put in an extra client.println()
    • This is an HTTP requirement and is really easy to miss.

SoftwareSerial problems

When using SoftwareSerial (on Uno, Nano, etc), the speed 115200 may not work. Try selecting 57600, 38400, or even lower - the one that works best for you. In some cases 9600 is unstable, but using 38400 helps, etc. Be sure to set correct TX/RX pins in the sketch. Please note that not every Arduino pin can serve as TX or RX pin. Read more about SoftSerial options and configuration here and here.

ESP32 Notes


When using ESP32 HardwareSerial, you may need to specify additional parameters to the .begin() call. Please refer to this comment.


You will not be able to compile the HttpClient or HttpsClient examples with ESP32 core 1.0.2. Upgrade to 1.0.3, downgrade to version 1.0.1 or use the WebClient example.


When using SAMD21-based boards, you may need to use a sercom uart port instead of Serial1. Please refer to this comment.

Goouuu Tech IOT-GA6 vs AI-Thinker A6 confusion

It turns out that Goouuu Tech IOT-GA6 is not the same as AI-Thinker A6. Unfortunately IOT-GA6 is not supported out of the box yet. There are some hints that IOT-GA6 firmware may be updated to match A6... See this topic.

SIM800 and SSL

Some, but not all, versions of the SIM800 support SSL. Having SSL support depends on the firmware version and the individual module. Users have had varying levels of success in using SSL on the SIM800 even with apparently identical firmware. If you need SSL and it does not appear to be working on your SIM800, try a different module or try using a secondary SSL library.

Which version of the SIM7000 code to use

There are two versions of the SIM7000 code, one using TINY_GSM_MODEM_SIM7000 and another with TINY_GSM_MODEM_SIM7000SSL. The TINY_GSM_MODEM_SIM7000 version does not support SSL but supports up to 8 simultaneous connections. The TINY_GSM_MODEM_SIM7000SSL version supports both SSL and unsecured connections with up to 2 simultaneous connections. So why are there two versions? The "SSL" version uses the SIM7000's "application" commands while the other uses the "TCP-IP toolkit". Depending on your region/firmware, one or the other may not work for you. Try both and use whichever is more stable. If you do not need SSL, I recommend starting with TINY_GSM_MODEM_SIM7000.


This project is released under The GNU Lesser General Public License (LGPL-3.0)