This build, from ajventi, is an automated potato and carrot farm which uses a villager to do your harvesting:

I made the thief device as a way to empty the inventory of a villager I had been using for breeding. Then I got an idea and built this farm. I think the redstone is very simple compared to other villager farms. Also because the villager is so diligent in his farm work, it’s incredibly effecient, he harvests as fast as his little villager feet can carry him to the newly matured crops

This farm is 9×27, but one farmer can plant and harvest this whole field and still end up waiting around for crops to grow, so I know it can be made larger, probably double the size. I have made a 31×31 farm in a creative world, but it seems it may be a bit large as his path-finding sometimes leaves him lost in a corner or ignoring crops on the outer edges of the farm.

I have a few things I think could be improved. First if I could reduce the horizontal footprint of the BUD switch it would allow more farmland to be placed closer to the harvest house.

Second, sometimes the villager falls when the piston retracts, and stomps the farmland. It does not happen too often, but at times I will have to re-till the soil on the thief plot. I have tried half slabs, fence posts, iron bars, and glass panes placed one block above the planting block, but they all stop him from planting. I’ve tried signs, but they did not keep him from falling.

Finally, you’ll notice my breeding chamber is very close to the farm, I’m sure I could add some switch activated mechanism to allow the farmer to throw food to the villagers, but I haven’t worked on that yet.

I hope people find this useful, and I hope maybe some of you can help make this thing perfect.

Redstone Detail

Redstone Detail

This is all the redstone. The sticky piston on the upper left acts as a BUD switch for the block above the farmland. When a crop is planted it retracts the vertical sticky piston, which harvests the crop (Potato, Carrot or seeds) and sends it flying in the air. The hoppers around the farmland are there to catch the planted crop. If you lock a farmer villager in this room, they will keep trying to plant on the farmland, and the “Theif” device will instantly harvest and catch the crop in it’s hoppers.

Inside the “House”

Inside the "House"

Here is the view of the thief plot. I have used a door to make it a house. However I have found it also works without the door, the villager AI at some point will detect the unplanted farmland and come in to try and plant.

Thief in action.

Thief in action.

The villager has just planted a potato, and the piston has retracted. Sometimes the villager will catch the potato before it lands in the hoppers, but most of the time the hoppers snag it first. Sometimes the villager will fall when the piston retracts and the farmland gets reverted to dirt. So you do have to keep an eye out and occasionally re-till the soil. I’ve experimented with half-slabs, fence-posts, iron bars and glass panes to try and stop this, but so far nothing has worked.

Farm overview

Farm overview

Outside the thief room I just have a simple farm. This is now 9×27. When I started I planted the entire farm and used bonemeal before placing the villager. So far I have found that the villager will eventually harvest all the crops to the point that he will be standing around and waiting for them to grow, so it can very likely be larger.

Farm Overview.

Farm Overview.

Here you see the villager out doing what he does.

Overview.

Overview.

Here is where I hang out in the village. This village is really a villager breeder, with a small trading outpost. I installed the farm when I got the idea and it has provided a very good supply of potatoes and carrots.

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