extended readme

README.md

+SOMO-II Arduino Library
+=======================
+
+An Arduino library to communicate with a SOMO-II module to play MP3 files.
+
+Usage
+-----
+
+Set up the required Serial object based on the pin connections
+you are using. Remember that the `TX` pin on the microcontroller board should
+be connected to the `RX` pin on the SOMO-II board, and vice-versa.
+
+```
+  RX (Arduino) ----------------- TX (SOMO-II)
+  TX (Arduino) ----------------- RX (SOMO-II)
+```
+
+When connecting to arbitrary pins on the Arduino, you'll need to use SoftwareSerial
+to create a secondary serial connection.
+In your Arduino Sketch, include and construct both the `SoftwareSerial` and `SOMO_II` items:
+
+```
+#include <SoftwareSerial.h>
+#include <SOMO_II.h>
+
+#define RX_PIN 8  // connect to SOMO-II TX
+#define TX_PIN 8  // connect to SOMO-II RX
+
+// set up a new serial object
+SoftwareSerial mySerial = SoftwareSerial(RX_PIN, TX_PIN);
+
+SOMO_II mp3 = SOMO_II(mySerial);
+```
+
+Or, if the SOMO-II is connected to a spare hardware serial port:
+
+```
+#include <SOMO_II.h>
+SOMO_II mp3 = SOMO_II(Serial1);
+```
+
+Start both the serial port at the required baud rate, and then call `SOMO_II::begin()`
+during the setup function:
+
+```
+mySerial.begin(SOMO_BAUD);
+mp3.begin();
+```
+
+or
+
+```
+Serial1.begin(SOMO_BAUD);
+mp3.begin();
+```
+
+This will start the SOMO-II module and set the volume to the mid-level.
+
+Playing MP3 files
+-----------------
+
+In it's simplest form, you can call `playTrack(track_num)` to play tracks based on
+the order they were copied onto the storage media, but if the tracks are arranged
+into numbered folders (eg. `001`) and the files have preceding numbers (eg.
+`001file.mp3`), then the `playFile(folder_num, file_num)` function is a little
+more useful.
+
+To change the volume, there are `volUp()` and `volDown()` functions to step up or
+down the volume range (0–30) in increments of 1, or the `setVol(volume_level)` to
+set it to a specific value.
+
+The functions are intended to be used with `feedback()` on (`feedback(true)`),
+currently the default, and they will then return a value based on if they are
+successful (`SOMO_OK`) or not, and will return the error code.