Congrats on the Teensy 4.0 release!

I'm working on a breakout kit for this, and I'd love to get some feedback before producing the first run.

Here's what I've got so far:

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Ok, so here's how this works: The brown board is a small (25 x 11 mm) flex PCB, which can be used either in a direct solder-to-board configuration, or socketed with a connector. I envision the Teensy side of the cable to be almost always soldered directly, but then the breakout side can be a connector when the Teensy is otherwise socketed, or soldered when it's not. The Teensy side of the flex cable can work with a connector too, as long as you're willing to forego the two USB host pins. I don't think I'll include a Teensy-side (8-pin) connector in any kits, whereas a planned socket kit will include a breakout-side (10-pin) connector, so the Teensy can be removed without any soldering.

The breakout is the same size and shape as my existing 3.2 breakout board. The scored "carrier" rails on either side are exactly the same. For space, the larger mounting holes have been removed, and only the mounting holes on the carrier rails remain.

There are pads for a tiny Micro SD card socket. I'm not sure how easy/hard it will be to solder these by hand, so we'll see. If it's impossible to solder by hand, I might offer an option of having it pre-installed for folks who aren't able to do SMD reflow themselves.

The VIN-VUSB switch is the same as it's always been.

There are some new pads on the bottom for a 12 mm coin cell battery!

Also, there are pads for a full-size USB-A connector for the host port, similar to my 3.5/3.6 Standard breakout. I have a question for folks about this though: For USB host power, I was thinking of just passing through VUSB, since the Teensy 4.0 doesn't offer any 5V output. Alternately, I could pass VIN directly as power on the USB host port. Or, should there be some kind of on-board little regulator to provide 5V? Let me know what you think I should do here.

I've never ordered flex boards before, so that should be pretty interesting!

All the best,