How to mount with hex risers?

[nzfarmer]

Ideally I'd like a solution to mounting your boards with 3M machine screws and hex risers.

Any suggestions?

thanks

[TomWS]

Ideally I'd like a solution to mounting your boards with 3M machine screws and hex risers.

Any suggestions?

thanks

Unless your Moteino is entirely standalone, there is probably some peripheral circuitry you need to add to it.  In this case, what works simply and reliably is a perf board (eg. https://www.amazon.com/gp/product/B0147YM3DG) on which you mount two single row sockets that will accept the Moteino header pins or, I prefer, round machined pin headers.   You can wire the peripheral circuits with 26-30ga wire connecting the joints and the perf boards will typically have a 3.2mm mounting hole in each corner.  With this setup the Moteino is pluggable for repair, replacement, or re-allocation to the next project.

[nzfarmer]

Thanks, I'll take a look!

[Felix]

Here's another idea:



Make sure to mount the pillars on something solid or they can slide off. I recommend nylon hex pillars for edge mounting to avoid shorting the pins at the edge.
Then you can easily slide/remove the PCB in/out if necessary.
You can even stack PCBs this way (even if they are not the same width).

[DonpK]

This topic brings up a something than annoys me about many (although not all) Arduino-style processor and accessory PCBs. This is what seems to be an obsession with making the PCB as small as technically possible - making them so small that there is absolutely no space left for mounting holes.

I understand that some applications require maximum compactness. But how often is it the case that adding several 0.126" (2.9mm) mounting holes is a game-killer for a project? The holes could even be placed in snap-off tabs on the board for those applications where minimum size is more important than ease of mounting.

[Felix]

DonpK,
Because such boards are panelized and machine assembled, any mounting holes would have to be placed inside the PCB outline. If that is really necessary, then a board like the small Moteinos which can't spare such large blank areas, would need to be extended in one direction or another. What % of users would actually use them ... I dont recall right now if anyone ever asked except in customized variants.
(FWIW - extension tabs with mounting holes are not feasible or practical for many reasons in a panelized/machine assembled PCB design - breaks a lot of DFM rules in my book.)

Anyway, let's take Moteino for example, size is a primary feature, but I have not obsessed to make it tiny like others do - just small enough to be practical. So, if mounting is necessary, the pin holes can be used either:
- soldered male/female headers to mate to female/male headers on a larger board
- as mounting holes in some clever ways, if they are free
- hot glue anyone? 

From what I saw in the years since I make Moteinos - I think most folks use the first method since:
- it's a development board although it's being used by many as actual brains in their end product
- you probably need headers anyway
- the board is small with virtually no mass and it's not like headers can't hold it very securely in most applications
- why bother with mounting holes in addition to headers

For any custom boards and end products mounting holes are customary.

[TomWS]

... But how often is it the case that adding several 0.126" (2.9mm) mounting holes is a game-killer for a project?

It's not the holes that take up the room, its the 6mm diameter clearance for the post that consumes the space.

The holes could even be placed in snap-off tabs on the board for those applications where minimum size is more important than ease of mounting.

If the 'snap off tabs' extend beyond the perimeter of the board, the PCB cost is now increased substantially.   For example, a 0.9inx1.3in PCB (like a Moteino) with tabs on the end for mounting holes, now becomes 0.9in x 1.8in, a 38% increase in area consumed by the PCB with no functional gain.

Now if Felix 3D printed a carrier that cradled the Moteino and provided a solid support for the mounting posts shown in his previous post, then maybe those needing mounting brackets can be 'supported', pun definitely intended...

[Felix]

It's not the holes that take up the room, its the 6mm diameter clearance for the post that consumes the space.If the 'snap off tabs' extend beyond the perimeter of the board, the PCB cost is now increased substantially.   For example, a 0.9inx1.3in PCB (like a Moteino) with tabs on the end for mounting holes, now becomes 0.9in x 1.8in, a 38% increase in area consumed by the PCB with no functional gain.

That and also:
- a 36x piece panel becomes a 20x panel, maybe less
- routed area in between boards means far less structural support for the panel
- very likely that snapping the finished PCBs out of the panel will result in snapped tabs - could be avoided by adding blank support columns (a minimum width of 1/8" per column) on the short side where there are no tabs = wasted-area++ && cost-per-board++
- all of the above would really call for internal mounting holes even if the resulting board is larger - I would really want to hear and see how/why people actually (plan to) use such mounting holes and where they would need them, before I even consider doing such a thing - I will say that the standard atmega328p Moteino outline and pinout will stay the same.

Now if Felix 3D printed a carrier that cradled the Moteino and provided a solid support for the mounting posts shown in his previous post, then maybe those needing mounting brackets can be 'supported', pun definitely intended...

Possible. I fear though that everyone will want that cradle to be a little different and in a different color/material/etc/etc and that's where the road can split in so many directions. Maybe a generic PCB with your mentioned mounts for the pillars, and maybe optional header mounts breakout pins inside/outside the board dimension, perhaps other pinouts or whatever ... a proto area .. ? That would be very generic and I could just order the PCBs without any SMT assembly required. I'm open to that but please continue the discussion and I want as much input as possible. Could even be a separate brainstorming topic.

I also thought of building some kind of 3D printed case to house Moteinos. How useful that would be is an afterthought but RE 3D printing little things like that ... here's my 2 cents: after doing a LOT of 3D printing for other projects, I think it's hard to justify the economics of 3D-printing when my main occupation and efficiency is doing something entirely different.

And BTW ... doesn't everyone have a printer these days? 
It's not like this is luxury anymore. For me, offering these may add a little cool factor to the product, but not a money maker. Offering the 3D model that the end user can customize and print in whatever way they want - wouldn't that make a lot more sense for me and the public? Maybe I'm thinking out loud here.

[DonpK]

Thanks Felix and Tom for the tutorial on the technical and economic aspects of PCB construction. Let me add that my mounting question was not just specific to Lowpowerlab products. It's applies to small boards from many sources.

I did a quick search and found one item similar to Felix's suggestion.

Perhaps a more flexible option might be something like the sketch I made. The tricky part of the standoff approach might be finding enough space to securely grab onto the edge of the board. The A, B and C dimensions of the sketch I made are what I'm referring to.

[TomWS]

I did a quick search and found one item similar to Felix's suggestion.

I like this one because it will provide corner mount (where it's easier to find an available edge and it's more secure).

@Felix, you're right, 3D printed parts aren't economically practical, but a .STL file might be nice to offer.  The problem I see is it requires an overhang, which is always a nuisance.  Need to think about this...

I doubt an enclosure would be useful.  There's more variability there than with the board mount!