Comment by ssl-3

The Teensy wasn’t engineered, tested, rated, or certified for any sort of continuous duty, let alone within a pressurized O2-enriched environment (assuming it was inside the vessel), especially not within deep sea Helium-enriched environments (that have been shown to break things like MEMS devices), and present unnecessary risks for an entirely inefficient choice (see: comment above, Teensy’s are ~$30-40/ea where small PCBs populated with the same circuit features can be had for under $20).

I’m probably not as qualified as the person you replied to, but that’s my intuition as someone with a passing familiarity with electronics engineering (I have an associates degree in EE).

People do whatever they want. It doesn't have to make sense.

Perhaps disturbingly: I even know of one bit of critical public safety communications infrastructure that is is expensive, low production volume, and has a Raspberry Pi 3 embedded inside. I won't name names because that's getting a little too close to home for my liking, but I was quite surprised to find this inside of a very nice waterproof box with chonky, expensive, olive-colored milspec connectors to connect it up to the outside world.

Which, well: Yeah. There's a ton of good reasons not to do that. But building a whole Linux system on a custom board using individual parts is hard, so it can make sense to buy someone else's work instead.

Except... that's what the CM3 is designed to provide, including on-board eMMC instead of an SD card. I'd not have been surprised at all if there was a CM3 in there, but there is instead an entire Pi 3.

But MCUs, like on the Teensy, aren't like that. They aren't hard to integrate on a custom board like the Broadcom SoC on a Pi 3 or CM3 is.

The primary purpose of an MCU is not to be stuffed onto a dev board like a Teensy, but instead to be stuffed onto the board inside of a microwave oven or an air fryer or a fancy remote control and be easy to interface with other things and to program.

It really doesn't take much to get them going: Some require external ROM or flash, but a lot of them have internal flash memory and only need power and programming pins wired up to let them run code and do whatever IO is needed within a system.

This camera already had at least one very custom board inside. It could have integrated the MCU, as well, instead of the kitchen-sink Teensy.

Doing so is not just style points; it's quite often easier, cheaper, and more flexible.

This allows a person to use all of the IO pins on the MCU to do stuff with, instead of just the functions that the designer of a dev kit decided to build out through whatever interfaces they decided to include.