Two years ago I built a fully-functional 3d ultrasonic scanner that used Teensy boards at the edge of their capabilities.
The scanner works by using a Teensy 3.6 to control an array of 80 independent 40khz emitters at a 25Mhz refresh rate to do acoustic beamforming and send a few-degrees-wide acoustic wave.
The sound wave then bounces on the nearest object contained inside the acoustic beam. It is then picked up by an ultrasonic receiver made with a Teensy 3.2 and a hacked HC-SR04 distance sensor.
A PC controls and synchronizes both boards to scan the whole environment of the sensor. It then does the signal processing and the 3d visualization of the sensor's environment.
A few photos:

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From the front: emitter array and receiver

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From the top: receiver on the left, shift registers + transistors in the middle, Teensy 3.6 and level shifter boards on the right

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The room and the scanner from below
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Bird from the right
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3d scan of the room : emitter is the red circle, and the room is viewed from the left. The color encodes the distance to the emitter.

Photos in the original size can be found in my original blog post.

- Detailed writeup on my blog
- Hackaday Post

- Github with schematics and code

Oh by the way, I'm looking for a six-month internship anywhere in the world from September to January. Let me know if you're looking for any interns with my skillset :-)