GSM remote control

IOT = Internet Of Things is no more a geeks only word. Many things are connected and controlled remotely via internet through all the channels now available: WiFi, 3G, 4G and still 2G when no high traffic is needed.
If even a very simple handshake is enough, something that can fit in a 160 characters packet, why not use the old, simple, cheap, wide spread SMS through the basic GSM network? Let's call it 1G.

Why pay if not used or used seldom? With SMSs only there is no fixed charge. Just a rechargeable SIM and you pay only the messages sent.

The need could be to control heating in a very remote location, where also an internet signal can be hard to receive or not stable.

The load can be activated also with just a fake phone call without any charge.
Your guests, if previously granted, can open the automatic door with any phone. No apps, no smart phone, no skill, no special keys needed.

OK. We agree that the GMS-SMS system is the right choice. But, there are a lot of available, ready systems to buy and install. Why we have to built it by ourself?

First of all because we all are makers. We want to understand how things work, not just use it. Once understood the basics of a technology we can hack it, adapt it to our needs or invent new, unusual application. So, the purpose of this project is to learn the fundamentals of this system, with some examples of practical applications.

One of the most common Quad-band GSM/GPRS modules used for this kind of operations is the SIM900 by SimCom.There are many board based on it, both standalone or as an Arduino shield.

We will use the cheap SIM900 Quad-band GSM GPRS Shield Development Board For Arduino for this project, but the code and examples are valid for any other board that uses SIM900.