Decoding GSM SMS Septets

Once encoding is done (refer to this post), decoding is easy.

First, we create two tables from the encoded data (like the encoding method), but for each 8-columns, we need to add empty column.

GSM Septet Decoding Tables

Encoding GSM SMS Septets

One part of the annoying thing in SMS is that you need to send the data in GSM septets (you may want to read it more in here and here).

There’s a lot of approach to encode your message to 7-bits GSM septets, but this is my approach to encode it without relying on java utils too much (which means that it’s quite portable for MCUs, like AVR).

Java GSM 03.38 SMS Character Set Translator

This simple class will translate ASCII ISO-8859-1 / Latin-1 character set into GSM 03.38 character set.

I build this class to add support for european characters in my SMS project (using ATMega128). Since the board haven’t come yet, I built it using Java first and will port it into C later (saves me a lot of time to build ArrayList-like class in C).