Please explain why this redstone minecart-loader works

Question

See attached images. I am proud that I was able to build this tool to make a chest-minecart pause while it gets loaded from a hopper, and when the hopper is emptied, the powered rail beneath it powers again and the minecart travels off. This construction is working perfectly. I admit I learned most of it from a video and slightly rearranged it.

The basic function is: When there is nothing in the hopper, then the various blocks cause the powered rail to have power. But if there is something in the hopper, then the various blocks cause the powered rail to lose power, so the minecart stops. It works great.

But, my problem is that I don't understand the logical sequence that makes each of the parts work in sequence!

Can a redstone genius out there please:

1. Look at the two attached images (one of the rail receiving power because the hopper has no items in it, and one where the rail is not getting power because the hopper has items)

2. Clearly explain the logical chain of events that makes it work. For example:

   • The hopper has something in it, so it causes a redstone charge to come out of it into the block next to it.
   • The redstone comparator then causes XXXX... this makes the YYYY...

Answer 1

Matthew Sheeler bubster20's answer is correct, but I wanted to expand a bit more on what each piece is doing here.

Comparators "read" the container behind it (a container being anything you can open and place items in, such as a hopper, chest, etc.). If there are any items inside the container behind, it sends off a redstone signal.

So, in the circuit above...items enter the hopper from the water stream. The comparator sees this and becomes powered, powering the block it is pointed into. This turns off the redstone torch on the other side of that block, which stops powering the redstone dust, repeater, and the block the repeater is pointed into, which the powered rail is drawing it's power from.

When the hopper is emptied, the reverse happens. The comparator stops sending a signal because the hopper behind it has no items, unpowering the block the comparator is pointed to, causing the redstone torch to turn back on. This powers the redstone dust, repeater, and the block the repeater is pointed into, which in turn powers the powered rail.

Answer 2

When a minecart stops at a rail, it is able to be filled with the hopper's items, making the hopper lose items. When there are no items in the hopper, the comparator turns off, which powers the block it runs into, which also means it turns off the torch. The redstone torch gives power to the redstone below it, which powers the next block, which powers the rail, and the minecart is released.

See these:

• https://minecraft.wiki/w/Hopper
• http://minecraft.wikia.com/wiki/Redstone_Comparator