A rather poor and noobish attempt by me (I'm not an expert in redstone stuff) to create an automatic mine-cart transport machine, powered by redstone. What it basically does is that the device will return the minecart back to you after it finished unloading stuff at the storage chest.

I believe this device could be useful for farming and mining if you cant be bother to take your items from minecart and store them manually in a large chest and if you need the minecart back.

Its not really a fully automatic machine, you still need to put your items manually in the minecart, then push the button. The minecart then will travel to its destination and the items in it will be unloaded automatically into a large chest via hopper.

Before that, the minecart will trigger a detector rail to produce a signal in which the signal will be delayed via series of repeaters. The delay will give some time for the minecart to unload about 85 items into a large storage chest. After that, the delayed signal will activate a powered rail and send the minecart back to you or its original location.

You can modify the machine to unload more than 85 items from minecart, by delaying further the triggered signal. This can be done by adding more repeaters, or employing other techniques to delay the signal more effectively and economically. I've seen a video in youtube where there is a redstone circuit design that can delay a signal up to 15 minutes or more.

Well, that is all. I'm pretty sure there are other more advance redstone devices by other minecrafters that can automatically transport and retrieve minecart better than my design, but I still want to share my creation no matter how feeble it is.

The download file for this creation is up and ready, in a form of minecraft schematic, so you may need software like the MCEdit and paste the schematic into your world.