SIM808

This library allows to access some of the features of the SIM808 GPS & GPRS module. It requires only the RESET pin to work and a TTL Serial. STATUS pin can be wired to enhance the module power status detection, while wiring the PWRKEY adds the ability to turn the module on & off.

The library tries to reduces memory consumption as much as possible, but nonetheless use a 64 bytes buffer to communicate with the SIM808 module. When available, SIM808 responses are parsed to ensure that commands are correctly executed by the module. Commands timeouts are also set according to SIMCOM documentation.

No default instance is created when the library is included

Arduino-Log is used to output formatted commands in a printf style. This make implementation of new commands really easy, and avoid successive prints or string concatenation on complex commands.

Features

Fine control over the module power management
Sending SMS
Sending GET and POST HTTP(s) requests
Acquiring GPS positions, with access to individual fields
Reading of the device states (battery, gps, network)

Why another library ?

There is a number of libraries out there which support this modem (Adafruit's FONA, TinyGSM for instance), so why build another one ? None fit the needs I had for a project. FONA is more a giant example for testing commands individually and I was getting unreliable results with it. TinyGSM seems great but what it gains in chips support it lacks in fine grained control over each modules, which I needed.

This library is then greatly inspired by FONA, which served as the reference implementation, but mostly only support the features I needed for my project and has been tested thoroughly and successfully in that configuration. It also tries to reduce the final HEX size as this was a real problem for the project it was built for.

It does not have the pretention to become the new SIM808 standard library, but can be useful to others as a source of inspiration or documentation to understand how AT commands works.

Debugging

If you need to debug the communication with the SIM808 module, you can either define _DEBUG to 1, or directly change _SIM808_DEBUG to 1 in SIMComAT.h.

Be aware that it will increase the final hex size as debug strings are stored in flash.

Usage

No default instance is created when the library is included. It's up to you to create one with the appropriate parameters.

#include <SIM808.h>
#include <SoftwareSerial.h>

#define SIM_RST		5	///< SIM808 RESET
#define SIM_RX		6	///< SIM808 RXD
#define SIM_TX		7	///< SIM808 TXD
#define SIM_PWR		9	///< SIM808 PWRKEY
#define SIM_STATUS	8	///< SIM808 STATUS

#define SIM808_BAUDRATE 4800    ///< Control the baudrate use to communicate with the SIM808 module

SoftwareSerial simSerial = SoftwareSerial(SIM_TX, SIM_RX);
SIM808 sim808 = SIM808(SIM_RST, SIM_PWR, SIM_STATUS);
// SIM808 sim808 = SIM808(SIM_RST); // if you only have the RESET pin wired
// SIM808 sim808 = SIM808(SIM_RST, SIM_PWR); // if you only have the RESET and PWRKEY pins wired

void setup() {
   simSerial.begin(SIM808_BAUDRATE);
   sim808.begin(simSerial);

   sim808.powerOnOff(true);    //power on the SIM808. Unavailable without the PWRKEY pin wired
   sim808.init();
}

void loop() {
   // whatever you need to do
}

See examples for further usage.

A note about HTTPS

While technically, SIM808 module support HTTPS requests through the HTTP service, it is particularly unreliable and sketchy. 7 times out of 10, the request won't succeed.
In the future, I hope to find the time to make HTTPS work with the TCP service. In the meantime I strongly (and sadly) recommend to stick with HTTP requests if you need reliability.

blemasle / arduino-sim808