Here i sagest to post some historical books about the mod time frame
Here is something : Sir James Cochran Stevenson Runciman s book about the fall of Constantinople by the turks http://www.librarything.com/work/154926 but it talks not only about the siege but also the political analyse of period between 1300 and 1500
Bulgarian holy martyrs- a bulgarian novel about the fall of the Empire of Tarnovo in 1393 and the battle of Nikopol http://www.pe-bg.com/?cid=3&pid=36869 the problem is that i still can't find a english version but as i soon as i fined one i will posted it.
Devastation- a book about the rule of the bulgarian emporer Ivan Alexander and the collapse of the Bulgarian empire in the begining of turkish invasion http://www.pe-bg.com/?cid=3&pid=26131