Epi 32U4

An extremely compact, Arduino-compatible ATmega32U4 USB Type-C dev board

Jun 21, 2023

Project update 5 of 9

Early History of the Epi Board Design and USB Port Torture Testing

by rallekralle

Hejsan and welcome to this fourth weekly update. I think. I’m losing count. Anyway, here’s a bit about the early two-layer Epi model and the USB port, which people keep telling me is fragile.

I’m not going to talk about the first couple of prototypes though. Too embarrasing.

That’s the fourth prototype, right before I switched over to a four-layer design. At this point the Epi was nearly a copy-paste of the Arduino Micro schematic on a smaller board. Sure it was functional, but some traces were way longer than they ideally should’ve been and were squeezed together as tightly as possible. It had no straight-forward ground return or power distribution. The board was a dense tangle. I also had to use a small 1005 diode since space was so tight. Those are not really affordable and are quite weak. You may also notice that there aren’t enough decoupling caps around the IC. There was no space.

At this scale and for this kind of device maybe that wouldn’t matter, but I’m not risking it. Four-layer isn’t much more expensive anyway. With that change I gained a lot of space and freedom to add protective features and I could spread out the traces at least a little more. Noise should be greatly reduced anyway thanks to the ground plane. The design is much less busy now and looks much better as well, in my opinion.

The USB port then. I was a little worried about its strength at first as well, but as soon as I had an assembled board i could tell it wouldn’t be an issue. Here’s a practical though crude example:

That’s roughly 1.5 kg at the center of the board, held horizontally by the port. Not bad I’d say. To be honest, I’m more worried for the cord.

Of course I had to push it. Here i hung the bottle at the far end of the board. It survived for a few seconds at least.

Maybe don’t try this at home, anyway.

See ya!

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Epi 32U4 is part of Microchip Get Launched

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