Automatic Gunpowder Factory
Video shows a high-speed demo, full walk-through of the wiring, and finally a flowchart of the whole redstone logic.
Fully automatic and produces ONLY gunpowder.
Included features:
Mob sensing- machine stays off when no mobs are present
Utilizes sunlight to burn away zombies/skeletons so only creepers are processed
Integrates an external day/night sensor to store up mobs at night and resume operation during sunlight
Automatic "junk" disposal- burns away loot dropped by zombies/skeletons to maximize framerate
Output enable lever allows creepers to build up so that gunpowder loot doesn't despawn