UBB

From Qi
Jump to: navigation, search

UBB stands for Universal Breakout Board, is a tiny PCB exposing the 8:10 card slot connectors to allow Ben Nanonote to connect to other electronic devices, DIY things, Arduino, SPI interfaces ... without need of soldering the BNN itself like the UART Approach.

It has three operation modes:

  1. 6 GPIO + 3.3. V power on/off;
  2. 5 GPIO + 3.3 V power on/off + clock output (frequency is configurable, up to at least 56 MHz);
  3. MMC/SD/SDIO

Contents

UBB production 05.JPG UBB production 08.JPG

[edit] Motivation

The motivation for making it is:

A bit of background on the latter point. Back when Rikard "discovered" the 8:10 card slot, there was a lot of discussion about how access to it could be made convenient.

One idea was to make an extension cable that would end in a 100 mil header that could then plug into a development board. Wolfgang had a few of these made in China as a "street job". This picture shows one, minus the 100 mil header:

This picture shows a "street job" cable, minus the 100 mil header

Alas, not much happened beyond this. Part of the problem may be that there are many different ways in which one may want to connect something to the Ben, and a 100 mil header, although popular and versatile, may not always be desirable.

Another issue is that, while the extension cable is simple, turning this into a proper product that can be made in quantity at a reasonable price and with good quality would be more time-consuming and more expensive than one may expect.

UBB dodges the issue of how to connect at the other end (more about this below), and addresses only the problem of getting the signals out of the Ben. Specifically,

UBB should be easy to manufacture and "productize" in general. (More about this later, too.)

[edit] For whom ?

Use of UBB is expected mainly in three areas: first, to make the Ben more popular as a "master" for circuit development, be this for hobbyists or professionally. The master would typically be a placeholder for some other device that connects in the final design or that may even be embedded in it, but the master may also perform temporary tasks, such as in-system programming and acting as a debugging aid.

Second, similar to the "master" role, aid in experiments where only a partial circuit is made, with the objective of examining certain properties or acting as a tool with a limited lifetime, but where this circuit is not intended to become part of a "finished" device. For such experiments, it's important to have a flexible "master" device. A small Linux system that can connect directly into the circuit while providing all the usual tools and infrastructure is ideal.

Third, lower the bar for experiments with extension circuits designed for the Ben. Such circuits could later become proper 8:10 cards or they could even be integrated into future NanoNote products.

[edit] Current Outcomes

There are already great outcomes from the UBB including:

[edit] The ribbon cable

A ribbon cable was chosen, because these cable are easy to obtain anywhere and they are quite versatile. Here are a few examples that illustrate possible uses in combination with ribbon cables:


And so on.

[edit] The anatomy of UBB

The drawing shows the various zones of the UBB board. From right to left:

An inserted UART board, showing the small gap between board and NanoNote.

[edit] Industrially producing UBB

The following areas need to be considered when taking UBB to a PCB fab:

Below are a few explanations that should help to obtain the desired results.

Disclaimer: I haven't interacted with a PCB house myself yet, so all this is based on theory and on second hand knowledge.
Disclaimer2:I have interacted with a a PCB house my self and this is too much information for the manufacturer :)  , give this page as reference  but give them just a sumarized part of the Industrially producing UBB, and the gervers in a more private_software-friendly format like zip files instead of tar.gz, as available here :P

[edit] Board material

The PCB is 0.8 mm (1/32") FR4 with 1 oz copper on each side. The surface finish would ideally be gold (ENIG), but tin-plating may be acceptable. Note that gold-plating, while sounding like something expensive, may not add significantly to the overall board cost.

There is one plated through-hole (PTH) via. The via hole has a diameter of 10 mil, but this can be changed to larger or smaller values if necessary.

Solder mask can and should be applied for appearance and to make it easier to solder the ribbon cable. (It's okay if the solder mask is scratched during use.) A silk screen should be applied.

[edit] Gerber files

When generating Gerbers, at least the following layers are needed to produce the board: Front, Back, Mask_Front, and PCB_Edges.

SilkS_Front (front silk screen) is strongly recommended - it contains labels, the project name, "qi-hw.com", and the license (CC-BY-SA).

The Comments layer is optional and probably best avoided. It has meaningful content if merged into the silk screen, but makes the board look a little crowded. Note that it also contains a drawing that's outside the board.

Mask_Back is optional (it's empty - the back is just one large ground plane).

There are two potential pitfalls when generating Gerbers with KiCad's pcbnew:

For reference, I've uploaded the latest Gerbers as http://downloads.qi-hardware.com/people/werner/ubb/ubb-gerbers-20110207.tar.gz

I recommend using "gerbv" to view Gerber files.

[edit] Cutting of the board

The board geometry has to be fairly precise. Tolerances of up to +/- 0.1 mm are probably acceptable, but more accuracy is better. Here are the general dimensions of an 8:10 card (all in millimeters):

8_10-card.pdf


The board outline is specified in the PCB_Edges layer with a 5 mil line whose center (!) is where the physical board edge should be. The following drawing illustrates this:

top.pdf

The yellow line is the board outline as drawn in the layout. The expected actual board surface is shown with black stripes. Here is a side view showing how the cutting tool has to be offset to obtain the desired result (not to scale):

edge.pdf

[edit] Panelization

In case the PCB house is unable to generate correct toolpaths with the data provided, I can also perform the offset calculation according to their tool specification.

The board needs an edge that falls off sharply. V-scoring would almost certainly yield undesirable mechanical properties and/or require extensive manual post-processing.

Since the UBB board is small, multiple UBBs should be made from a single board. For this, the UBBs have to be arranged in an array, according to the specifications provided by the PCB factory. If the PCB fab can do this themselves, even better.

If the PCB fab cannot produce a cut that goes all around the UBB board, it needs to remain attached at some point to the original PCB. This is often done with a perforated bridge that is later broken off. The following drawing shows which areas of UBB are more or less suitable for placing such bridges:

[1]

The red zone should be avoided, because it would be difficult to remove any remains of the bridge. The yellow zone is easier to handle. The green zone does not need cleaning.

[edit] Results

Production final caracteristics:

[edit] Sources

Mailing list posting that is the source of the information on this page.

Gerber files generated from KiCAD

Sources of UBB in Qi-Hardware repos

Personal tools
Namespaces
Variants
Actions
Navigation
interactive
Toolbox
Print/export