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Are you looking to build LEGO systems controlled by Python and a Raspberry Pi? The Raspberry Pi Build HAT is exactly that. An adapter board that takes the standard RPI 40-pin GPIO header and enables connecting LEGO® Technic ™ motors and sensors.
We’re always looking to connect a Raspberry Pi to the real world, and LEGO Technic can be a great platform to build all kinds of gadgets that work with motors and various sensors. The software runs on Python and .NET, so it’s easy to get started control things.
The board retails around $25, which is a pretty good value for anyone wanting to build with Lego Technic using a Raspberry Pi as opposed to the many other closed platforms. You could build your own, but this is an easy path to the tried and true.
Be mindful that you should almost certainly need to buy the external Raspberry Pi Build HAT power supply which isn’t included. Since Raspberry Pi boards provide limited power for motors, you will need the 48W power supply which is $15, setting you back $40. Note that you can also use a 7.5V battery pack for when you want the LEGO to run independently.