Particle Tachyon SBC modular case

This is a custom box for the Particle Tachyon single board computer (SBC).

This computer has the Raspberry Pi form factor, but does not use the exact same port, so a tailored case was in order. There are several variant of the model to support the optional use of the Particle audio extension board, of a PCIe extension board beneath the SBC, or of an external battery holder.

Models

• The case_xxx.stl models are the bottom part of the case:
  • Those with with_battery in their name (in the With battery holder folder) have attachment points for an optional battery holder. The others (in the No battery holder folder) are meant to be used without the battery holder.
  • Those with with_base in their name have the space to fit the Pimoroni NVMe base (or probably any other type of PCIe base that would go under the board).
  • Those with with_audio in their name have opening to fit the audio adapter board.
• The cover_xxx.stl files are the top cover of the case. They are both compatible with all the versions of the case. The with_battery one has an additional hole to route the battery cable.
• The power_button.stl file is what it says, it fits in a hole aligned with the SBC power button, to allow to turn it on or off.
• The battery_holder_N.stl files are the battery holders for 1 and 3 cells battery. Meant to be attached to the side of the case.
• The standoff_audio_board.stl file is a standoff (or spacer) that is meant to fit between the main board and the audio adapter board. You should print 2 of these if you want to use the audio adapter board.
• The standoff_base.stl file is a standoff meant to fit under the main board, between it and the PCIe extension board. You should print 4 of these, or you can use the standoffs that are provided with the Pimoroni board if you use that one.

Print settings

• For all the pieces, I recommend printing them in PLA, with 0.20mm layer height.
  • Printing in PETG or other materials would certainly work too.
• If you print the case_with_battery_xxx files, then you will need supports. You should paint support on the under sides of all the side connectors for the battery holder (on the 3 pairs of prongs that don’t exist on the case_no_battery_xxx files). I use “adjusted” supports for that.
  • Be sure to paint the under-side of both prongs of each pair (so 6 in total). In PrusaSlicer at least, the smart support painting makes it super easy to add them.
• You also need supports for the connectors at the top of the battery holder itself.
• You should not need supports anywhere else.

Post-processing

The only post-processing needed is to remove the supports on the connectors for the battery holder. To be honnest, this is not that easy with this design. To remove the support, I use a small hobby knife and a metal spudger like this one.

The PCB for the Pimoroni NVMe board that I have had some left-over from the paneling on its side. I sanded them away with a wood file to shorten the board a little, although this might not even be necessary to fit it in the case.

Assembly

Case without support for the PCIe extension board

For the assembly you will need some flat-head M2.5 machine screws and nuts. If you are not using the PCIe base, then you need 4 10mm screws, or 2 10mm ones and 2 16mm ones if you are using the audio adapter board.

Case with PCIe extension board

If using M2.5 threaded standoff of 8mm long between the Tachyon and the PCIe extension board (like those provided with the Pimoroni NVMe base), then you will need 4 8mm flat-head screws and 4 rounded (non-countersunk) 4mm screws. If you are using the audio extension board, then you will need 2 10mm screws instead of two of the 4mm ones.

If you are using the standoff provided with this model you can use 4 flat-head 16mm screws. But the assembly isn’t easy in that configuration so I’d recommend using threaded standoff instead.

If you are using the PCIe base, then you will need 4 16mm screws (or shorter ones if you are using the threaded standoff provided by Pimoroni).

Battery holder

The battery holder can also be fastened to the case with flat-head M2.5 machine screws. You will need 3 screws of 10mm and 3 matching nuts.

Note that the nuts are rather difficult to put in place. If needed, you can just omit them, as the screws will already hold pretty well without them (in that case you can go down to using only 8mm long screws.

I’m adding a small piece of blu-tack or equivalent on the battery, to have it stick in the holder.

Future improvements

Here is a list of possible future improvement. Let me know if you need any of this:

• Allow to use the 40 pins GPIO header (although you can just use the case without its cover).
• Some mounting points for QWIIC/Stemma QT boards.
• Snap fit connection for the battery holder.
• Snap fit connection for the Tachyon and the PCIe extension board.