User:MentalMouse42/Sandbox/Water Clock - minecraft.fandom.com

This is a pseudoclock based on the "water timer". It adds 3 hoppers and 2 extra droppers to recycle its items, so that it never needs to be reloaded. It takes 8×11×5 (only one block on level 5), and has a period averaging about 23 seconds. The top dropper should be loaded with several items (a batch of sticks will do fine). With 3 toggles and an inverter, it should do fine for announcing a furnace change for either a coal blocks or a lava bucket.