Connect-4 Minecraft Mini-game

This is a project i made 100% alone in 1 day . I am quite proud of it as i made it by hand with no schematics and i beleive that no one else has a copy or redstone Connect-4. the main game is a 7x6 blue square onto which gravel for player1 or sand for player 2 is dropped in stead of counters in the real game. the system uses 3 layers of 7 pistons to which select either sand or gravel for 2 of the layers then the 3rd layer drops 1 piece of the selected block. i also tried to make a fool proof system of protecting the wiring as if both players flick there switch it would mess up ... so i added redstone lamps to indicate whos turn it is and pistons to actively block the current through the redstone as a fail-safe.