Archive for the ‘Products’ Category


“Rev 1” Xmega adapter art


I’d mentioned a post or so back that I found assembly costs to suffer from the use of QFN chips, and that I was going to redesign the Xmega adapters to use PQFP instead.  Here they are:

I call these the “rev1” boards because the first round of QFN’s were the real functional test.  These boards have identical schematics, just different parts implementing it.  The pins are now surface-mount on the bottom of the board, which doesn’t even come close to offsetting the costs of the QFN when it comes to assembly (quoted at Screaming Circuits).  I’ve also switched the A3 boards back to 0603 caps, since while I can do 0402’s by hand (the first rev0 A3 board is assembled and working as well!), I don’t think they’re going to scale well for production.  They spend half their time stuck to the tools instead of the board…

I’m going to turn a set of 3 of each of these with the next group order to make sure I can do the bottom-side headers, then these will be the “final product” boards until something else needs to change…


Xmega board up and running!


This morning I soldered up the first of the A4 boards, and it works great so far!  I’m working on thorough “boundary scan” testing in the form of hooking up LEDs to each of the pins and making sure the chip soldered properly, and if that passes I have a perfectly functional board.

For those who got boards and parts kits last night at DorkbotPDX, here are ZIP files of the final Eagle and Gerber files the boards were made from:

One thing I forgot to mention to everybody is that the crystal has to be connected via a pair of solder jumpers right up against it.  The soldermask is supposed to be missing from between them, and the gerbers show that it’s supposed to be, but the boards look like they have some in there anyway.  What it boils down to is that you need to make sure you glob plenty of solder in there, either paste or after the fact.

After some research into the costs associated with making these in quantity, I came to the conclusion that a redesign was in order, to use the PQFP parts instead of QFN.  The resulting boards are a hair wider, and use surface-mount headers on the bottom, but are schematically identical to this first batch of boards.  The A3 version might actually end up being a 900mil board though, since the PQFP-64 isn’t liable to fit on even the wider 600mil board…  The resulting boards will end up my upcoming webshop, hopefully within a few weeks.


Xmega adapter boards for breadboarding


I’ve got a number of projects coming up that would be radically simplified by a) using ATXmega parts, and b) breadboarding a prototype.  The problem is that Xmega’s don’t come in anything but surface-mount packages.  The obvious solution is to construct an adapter board.  A straight pin conversion would be a waste of effort, so adding programming headers, clocks, and decoupling capacitors is a necessity.

I posted to the DorkbotPDX list to see if anybody is interested in ordering some of these alongside my own order in the next group PCB buy (April 26th), and got one response almost immediately.  As a result I’m going to tweak the boards up and make sure they’re ready to go, and post them up here for comments.

The first board here is the ATxmega*A4 unit, which is a 40-pin 600-mil DIP.  PDI header on the right, crystal on the left, decoupling and AVCC filter caps scattered around.  Port pins are labeled as are + and -.  PDI pins are accessible on the main header as well as the programming header.  Discretes are all 0603 for ease of assembly, though the chip itself is a QFN (unfortunately).

The second board is a straight extrapolation of the first, designed for the larger A3 chips.  It’s a 60-pin 600-mil DIP with the same basic feature set.

I’ll be tweaking these over the next few days, and hopefully producing a batch of them in the next couple weeks.


Isolated USB cable, hub


The next design I’m showing off is a tiny little board (1.4″ x 0.45″) that houses both an ADuM4160 USB 2.0 low/full-speed isolator, and an ADuM5000 100mW power isolator.  The two together form the core of a fully-isolated USB cable, which means you can safely connect your externally-powered device to your computer without any worries about where the relative ground potentials are.  This is critical for my main contract, because each board takes power from further and further down a main power bus, which means that even after the regulators do their thing, the ground potential on each subsequent node on the wire is different from the previous.

The ADuM4160 requires power on both sides of the transformer isolation barrier to run its encode/decode circuitry, which is why the ADuM5000 is required to provide power.  The upstream port of a USB device does not provide any power to the cable, so there’s no power for the device side of the isolator without the ADuM5000.  However, the 100mW limit means you really can’t run most bus-powered devices off the isolator.  OTOH, why would you be putting a ground isolator on a bus-powered device anyway…?

Isolated USB cableThe other design is a 7-port USB hub based on the same concept.  The upper-left port is the upstream, the remainder are downstream.  All 8 ports are fully isolated for both USB and power.  The 100mW limit of the upstream ADuM5000 should be sufficient to drive the 7 downstream ADuM4160/ADuM5000 pairs as well as the TUSB2077A hub chip, but not provide any power at all to even the lowest-power of devices…

Isolated USB hub

I haven’t had luck yet getting the cable isolator to work, due to a combination of problems not the least of which was the lack of proper silkscreen in the parts library footprint I stole.  It helps if the ADuM5000 isn’t backwards, eh?  I haven’t gotten back to trying to finish that because the memories of spending a week bashing my head bloody against the problem are still too painful.  I’ll get to it soon though, because I will need a quantity of them very shortly.  The hub is still sitting on my desk as a bare PCB, since I don’t really want to start sticking some $70 of parts on the board until I know the smaller version works…

Once they are confirmed working, I plan to offer them for sale somehow.  I know there’s interest, because only a few days after posting to the DorkbotPDX list about them, I got an email from someone entirely unrelated to dorkbotpdx about wanting to buy some. Go Google!