OpenBCI – Research grade EEG put together by an ad-hoc community. OpenBCI is a powerful Arduino compatible open source hardware design. Prices range from $350 – $1,100 depending on how much you can print and assemble yourself. The current OpenBCI headset uses 10 gold electrodes.
There is some potential for the Muse and Emotiv brands of EEG headbands to be used for DIY brain control interfaces. These headbands are in the $250 – $800 range. Muse has some (1) (2) github Arduino oriented projects. There is an unmaintained python library for Emotiv that was reverse engineered to work with a Raspberry Pi or BeagleBone Black.
Make a robot friend with Adafruit’s CRICKIT – A Creative Robotics & Interactive Construction Kit. It’s an add-on to our popular Circuit Playground Express, FEATHER and other platforms to make and program robots with CircuitPython, MakeCode, and Arduino. Start controlling motors, servos, solenoids. You also get signal pins, capacitive touch sensors, a NeoPixel driver and amplified speaker output. It complements & extends your boards so you can still use all the goodies on the microcontroller, now you have a robotics playground as well.