I build this command without any generators. It took me 12 Hours and it's my 1st 1 Command creation. now it on version 3.1 there will come a 4.0 version where u can choose the radius of the explosion by just right-click a sign. HAVE FUN !
THE MACHINE WILL SPAWN ~0 ~0 ~2 SOUTHWARDS (Z+) OF THE COMMAND BLOCK U PLACED.
1. Type in chat: /give @p command_block
2. Place the command block, stand against it then copy the command below and paste it into the command block.
3. Click on the "needs redstone" button so it will change into "always active".
4. after 0.5 seconds everything should be done and if u read these things good u wont be stuck into it.