ramdom generation split in to kind 
 

pseudo ramdom :
 
                       this is a good exemple from Tim Boescke - t.boescke@tuhh.de
 
 
 

real ramdom :

                    the real ramdom is mostly generated by analog circuit like this

this is the code for the avr circuit  the working is prety simple the 2 trasistor generate a white-noise of 180mv
this signal if feed to capacitor for remove the dc bias end feed to avr comparator input 1 the resistor divider
put 100mv on input 0 the code juste sample the comparator ouput ent store it to a register :-) that all