Stacking 2 SEEED Audio Mezzanine boards on the Dragonboard410C

This Audio Mezzanine board is very helpful in bringing out the low speed header on a 2.54 pitch 40 pins header in the middle of the board.
I intend to stack a second one on top of the first and use that header as a convenient way to bring out many of the GPIO pins and connectors. So if I break something I only need to take out that extra Audio Mezzanine instead of replacing the Dragonboard410C itself.
I will use a set of more than one Audio Mezzanines for a variety of pre-build circuits and swap these around. As the first Audio mezzanine sits safely in the Dragonboard the main connectors are safe.

What do you think? Would this technically work?

Thanks for sharing your thoughts on this setup.

@waterwin.
If I understand correctly what is your intention, stacking 2 mezzanines together directly will electronically short circuit the IN/OUT and in the case of output will brick the boards.
:frowning:

Merci beaucoup for your quick and clear reply. Just yesterday I played YouTube open hours #48 and #49 with your community minutes, :wink:

Very interesting world.

But you can stack another board on the audio mezzanine. I will really have to look into the details of the circuit and the connectors. The only interconnection would be via the lowspeed and high speed connector.

Regards from Meuse.

You can stack mezzanines (1, 2, 3…), but only few existing ones are stack-able. You need to pay attention to pins assignment in order to avoid conflicts, shortcuts, unwanted impedance increase, etc… For example, the audio mezzanine already routes the debug UART to FTDI, so you probably don’t want to use/route the related low-speed pins on upper mezzanine(s)…

Thank you Loic.

But what then is the added value of the stackability based on the Mezzanine overall design.

And is there a list of combinations that can be stacked?

Or maybe nobody needs stacking as all projects need 1 Mezzanine at max.

Erwin

The added value is that you can add multiple mezzanine boards that implement different functionality, just so long as they don’t both try to use the same pins for different purposes.

For instance, you can use several boards that implement different i2c devices since they can coexist on the same bus (as long as there is no address conflict). Or one board that implements an i2s audio device and a second that implements gpio level shifting.

One of the things that take away from stackability, is implementation of “generic” features. For instance, so many boards implement a usb-to-uart connector, which, imo, should only be implemented by one board in the stack.

I usually see Audio Mezzanines stacked under Camera cards. The Audio Mezzanine gives access to the serial debug port, and the camera mezzanine does camera stuff. This is the ‘normal’ use for stacking mezzanines.

When you do stack on top of an Audio Mezzanine be sure to disable the level shifters to the 0.1" 40-pin header (there is a switch on the Audio Mezzanine board to do this). The Audio Mezzanine board does pass the high speed connector signals through, but most of the mezzanine boards do not pass through the high speed connector.

As far as using the physical connectors on the Audio Mezzanine to protect the physical connectors It is unlikely that will wear out the connector, you are far more likely to kill your board with an ESD event while plugging and unplugging.

-Lawrence-

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