Arcanon

This item appears to be a metal pack worn on ones back, with a 2 foot diameter glas sphere protruding from the back.  A rifle-like device with 5 clear crystals alont the stock.  You can use the cannon to cast one of the following spells:  Chromatic orb (1 charge), Flaming Sphere (2 charges), Scorching Ray (2 charges), Fireball (3 charges), Lightning Bolt (3 charges), Sleet Storm (3 Charges), Ice Storm (4 charges), Wall of Fire (4 charges), Cloudkill (5 charges), Cone of Cold (5 charges).  These spells are cast at their inimum level, have a spellcasting modifier of 5, and a spell save DC of 15.  The Arcanon has five charges, one for each crystal.  You can replinish a charge by siphoning a spell slot into the Arcanon.  For each level of spell slot the Arcanon gains one charge.  The Arcanon cannot hold more than five charges at a time.  For each level of spell slot siphoned into the arcanon, one of the gems lights up with a color matching your domain of magic.

Notes: You must be a spellcaster to attune to this item. You must also have at least 12 hours of professional training, or 24 hours of self-taught training.