Beamspring USB controller

[Parak]

Neat, though sadly this makes hand soldering them quite difficult what with that center pad and all. I guess that's why you have a reflow setup :p

[nourathar]

ok, ordered the weird connectors and will order PCB's and parts tonight for a rev03 board. I am ordering everything to make three, so I can ruin one and still have a spare one if all goes well...

Also took the time to read the whole thread from the beginning, and came across this description of how to replace the contamination shield:
http://geekhack.org/index.php?topic=46134.0
Did anyone try this with a slightly more 'noble' material ? I am going to try and find something more rubbery or latexy, but it has to be very supple indeed if it is not molded like the original. But then again Amsterdam is probably not the worst place to look for rubber or latex..

ciao,

J.

[Muirium]

But then again Amsterdam is probably not the worst place to look for rubber or latex.

Aha! If you find something just right, do tell the rest of us about it. No need to mention the particular dungeon you found it in if you don't want to…

[wcass]

ok, ordered the weird connectors and will order PCB's and parts tonight for a rev03 board. I am ordering everything to make three, so I can ruin one and still have a spare one if all goes well...

Also took the time to read the whole thread from the beginning, and came across this description of how to replace the contamination shield:
http://geekhack.org/index.php?topic=46134.0
Did anyone try this with a slightly more 'noble' material ? I am going to try and find something more rubbery or latexy, but it has to be very supple indeed if it is not molded like the original. But then again Amsterdam is probably not the worst place to look for rubber or latex..

ciao,

J.

LMAO!

McMaster has it in 6 mil and it is relatively inexpensive. The elasticity might help prevent wrinkles and make it easier to work with.
http://www.mcmaster.com/#8611k11/=qa15ne

[nourathar]

impossible now to resist posting this:


from:
http://www.buylatexsheeting.com/alllatex

[fireglow]

Rawr, I <3 Latex

[xwhatsit]

Neat, though sadly this makes hand soldering them quite difficult what with that center pad and all. I guess that's why you have a reflow setup :p

Well, not so... I started looking at using these before I built the toaster oven. The nice thing about 74AHC series in DHVQFN16 is that regarding the centre pad (quoted from section 6 of datasheet):

This is not a supply pin. The substrate is attached to this pad using conductive die attach material. There is no electrical or mechanical requirement to solder this pad. However, if it is soldered, the solder land should remain floating or be connected to GND.

I put a tiny wee bit of paste on the centre pad but the pad is not hooked up to anything on the PCB.

I would have no qualms about hand-soldering these; after seeing the way everything flowed when I fluxed and hoof-tipped the pads to fix some bridges, they seem much friendlier than something like the 4-pin crystal I used on Rev1–2. It's weird how the smaller things get in SMT, the easier they are to deal with (unless you're talking stupid stuff like BGA ). I'll have to give 0603 caps/resistors a go next, as I suck hand-soldering 0805s; maybe they'll be easier!

[nourathar]

ok, the original rubber shield was 0.17mm thick, and most latex in Holland actually comes from here (UK):
http://fourdrubber.com/
who have a webshop here:
http://www.supatex.com/index.php?option ... &Itemid=73
where they have thicknesses starting at 0.16mm, which is more or less the same as 0.006".
I might order some of this stuff and see how it behaves. Now I have to choose a colour: white, red, brown, black or baby pink ??

[Compgeke]

Baby pink, it's the best.

[Parak]

The trick is that it needs to be /very/ thin and stretchable. You need to make these little domes around each switch, and then put the keycap on which will stretch it further, likely tearing it since it's a very tight keystem fit to rather sharp metal bits. The one nice thing about poly is that it's dirt cheap - so it's easy to buy a sheet then throw it away when needed at next cleaning of keycaps or something.

[nourathar]

EDIT: permalinks to Rev2 & Rev3 boards on OSHPark

thanks a million for putting those up, that is extremely convenient en I'm also surprised by how cheap they are.
Pretty amazing if you say the quality is very good.

@parak:

yes, I was thinking about that too and I was pondering ways to not fold the stuff around the metal stem part on which you slide the keycaps, but to make a neat slit and have it stay under the keycap. Which is perhaps a bad idea because it is less tight and which might tear anyway. I don't know, I'm not in a hurry either, and I guess the most reasonable would be to try out some dirt cheap plastic first before ordering a roll of shiny pink latex.

[nourathar]

boards are on their way, can't wait...

[nourathar]

beamboardconnector.JPG (309.63 KiB) Viewed 7017 times

boards arrived !
and hmm, the connectors arrived too, but it turns out that I ordered not 3 of those, but 30 !

so I have a bunch (27, to be precise) of spare connectors here in Amsterdam, and I am happy to send them to anyone who needs some if you pay shipping (which should be just a few euro's inside of Europe).

duh,

J.

[nourathar]

I am now ordering the parts for a rev3 board (from farnell / element14), according to the list in the beamspring-usb_0.5a.tar.gz I downloaded. Most of it is very clear, but there are three things I do not understand, apologies for bothering:

- is it true I need 2 resistors of 22 Ohm ? not 22K ? (it says 22 everywhere, so I guess this is a really stupid question)

- I found the Abraconn ABM8G series, but the footprint (4 connections on the corners) does not seem to match what I see on the pcb or what I see on the pictures: there I see two connections and a more oldfashioned crystal shape, so what do I need ?
for the Abracon ABM8G documentation see here http://www.abracon.com/Resonators/ABM8G.pdf

- also the switches are different, these http://nl.farnell.com/te-connectivity-a ... FSM+switch match the description in the part list, but they are 6mm long, not 2mm as on the pcb. I see these on the pictures early in this thread, but then I guess those are not rev03 boards ? Which ones should I use instead ?

and for now it seems the atmega is out of stock overhere, so it will take 10 days. Wish I had ordered these before !

thanks !

J.

[nourathar]

OK I've more or less done Rev3 PCB layout, which has a few changes from Rev1 and 2:

• Removal of pushbuttons for Program and Reset. There are test pads instead.
• Larger HC49-style crystal instead of the special tiny thing that was used before. Saves some cost.

found this buried deep in the thread, so the crystal is different now and the switches have gone.

and there is even a picture of it:



so, if I am correct the parts list for rev03 is:

(all caps & resistors are 0805 size)

1x 1uF ceramic cap
7x 0.1uF ceramic cap
2x 18pF ceramic cap
1x 4.7uF ceramic cap
7x 10K resistor
2x 4.7K resistor
2x 22 resistor
4x 100K resistor
1x 47K resistor
1x 16MHz crystal, footprint matches this: http://www.farnell.com/datasheets/1658661.pdf
1x Mini USB connector (most seem to have same footprint, but like this:
http://portal.fciconnect.com/Comergent/ ... 033526.pdf)
1x Atmel ATmega32u2 (TQFP32 footprint)
1x MCP4726 (SOT23-6 footprint)
3x 74HC4094 (SO16 footprint)
1x LM339 (SO14 footprint)
1x 3.96mm pitch 2x30p edge connector, such as: http://www.ebay.com.au/itm/140887820225
(and of which plenty are available in Amsterdam too )

[xwhatsit]

Ahhh sorry, I should keep that BOM up to date. Generally most reliable source of information is the Kicad project itself.

Definitely 22 ohm btw. I'm pretty sure they're for signal termination (reducing reflections etc.); Atmel says `put them on' so that's what I did.

Let me update that BOM because there's also a new DAC and different resistors in some places and I would recommend a higher-spec comparator than the base LM339 (I'll highlight the changes):

1x 1uF ceramic cap
7x 0.1uF ceramic cap
2x 22pF ceramic cap
1x 4.7uF ceramic cap
7x 10K resistor
2x 20K resistor
1x 4.7K resistor
2x 22 resistor
4x 100K resistor
1x 47K resistor
1x 16MHz crystal, footprint matches this: http://www.farnell.com/datasheets/1658661.pdf (HC49US crystal, very standard size)
1x Mini USB connector (most seem to have same footprint, but like this:
http://portal.fciconnect.com/Comergent/ ... 033526.pdf)
1x Atmel ATmega32u2 (TQFP32 footprint)
1x DAC101S101 (SOT23-6 footprint)
3x 74HC4094 (SO16 footprint)
1x LM339A (SO14 footprint)
1x 3.96mm pitch 2x30p edge connector, such as: http://www.ebay.com.au/itm/140887820225


BTW: nice job with the connectors! I got 10 but only because they were cheaper that way... 30 is a good effort!

[nourathar]

Hi xwhatsit,

ah great, thanks for clearing that up, I completely didn't think to look at the Kicad project, since I don't have the software to properly look at it and I did not realize that there is a partslist in there that is very much human readable. Learned something again !
I have trouble finding the new DAC, in that Farnell does not have it; only a replacement that would have to come especially from the US, this one:http://www.farnell.com/datasheets/1771327.pdf
And I am not super enthousiastic about paying 25 euros to ship three ant-sized bits of electronics...

would it work with the old comparator ?
I can look around at other vendors, but if Farnell doesn't have it, that doesn't bode well in my (admittedly extremely limited) experience..

thanks a lot, J.

[xwhatsit]

Uhoh!

I was surprised when you said that, as I use element14 (which is Farnell) here in NZ. The element14/Farnell part code for that DAC is 1559747. However it's showing out of stock! Weird! Has TI stopped making this DAC? Will do some research.

Unfortunately it won't work with the old DAC, as the MCP4726 is I²C, not SPI. The firmware could probably be modified to bit-bang I²C over the SPI lines, as long as the pinout is the same. But still not ideal.

I wouldn't be surprised if there was another SPI DAC with the same pinout. I'll have a look.

EDIT: RS in the Netherlands have it, but want you to buy 5 at the price of €2.534 each! http://nl.rs-online.com/web/p/general-p ... 4E4F4E4526

EDIT2: TI are saying it's still a current production part. Farnell must just be out of stock (they are saying lead time of 44 days!?!?). TI have it on their website; if you were cheeky, they're offering free samples as well of the correct package, so if you're nice they might send you a couple.

[nourathar]

Uhoh!

EDIT: RS in the Netherlands have it, but want you to buy 5 at the price of €2.534 each! http://nl.rs-online.com/web/p/general-p ... m=651-2155

ah ok, that is great, at least for me for now: I hope this part is not discontinued !

That price is ok actually :
in Dutch, the point and comma are used the other way around as in English, so the price is 2.53 per IC if you buy 5..

thanks a lot,

J.

[xwhatsit]

Yup I know about the comma/decimal (you have no idea how much parsing code I have to write in my day job to deal with differences like that! Pales in comparison to turning crazy fractional inches in mm though...)—still sounds expensive to me. I bought them for about $NZ2.69 each in single quantities. I have one left in my little box, but by the time it's posted overseas it would be more expensive than buying 5 from RS.

Yes you can use the DAC121S101 btw. You just have more output resolution (not a bad thing). I will have a look for other DACs in Rev4 (which I have actually done a bit of work on... just not enough to get anything ready before I head overseas for 3 weeks for my wedding).

Not a bad rationale for moving to something like an STM32 instead of the ATmega. Many of the STM32s have integrated DACs. Only problem, 3.3V instead of 5V; I like the 5V as the drive pulse for the capacitive sensing is a bit more grunty.

[nourathar]

haha, and I was assuming that's why you found it expensive..
(and it fact it was me being confused by the comma/point swapping..)
I'm just going to go ahead and order those DACs from RS, thanks a lot for finding them before I even started looking !

and congrats with the wedding btw. ! That is a nice thing to head overseas for, and three weeks !

[webwit]

Wink wink. Nudge nudge.
I have a feeling there might be coming some 60%'s out of that.

[nourathar]

still waiting for the atmega chip, after more than a month !

I ordered this one http://nl.farnell.com/jsp/search/produc ... KU=1748524 which has been on back order for all this time and farnell tells me it will not be available until end of April, which is ridiculous. Was sort of busy recently, but now I found another supplier who has them and will order from there....

[scottc]

I've only ever ordered from Farnell once, and it was for the same reason...

[nourathar]

I've ordered from them a couple of times and mostly it's super rapido; this is the first time this happens !
I guess I should simply be more careful to check their stock before ordering, I thought I did....
Ordered elsewhere now, will arrive on Monday..

[xwhatsit]

Yes the ATmega32U2 has been out of stock worldwide across most distributors. At work one of our subcontractors produce a board I designed which uses one of those chips (they're so damned useful!) and they even went to the extreme of ordering some from a dodgy Chinese supplier; the boards wouldn't flash, it turned out the chips were just re-silkscreened fakes.

In the end they used the ATmega16U2 instead (I originally designed the board for the ATmega8U2, but the 32U2 is normally much more common and often has better pricing).

Sorry still no progress on Rev4. Just came back from 3 weeks in overseas wedding, returned with bronchitis, now time for local wedding this weekend... which was planned to be outdoors... a tropical cyclone is supposed to hit tonight or tomorrow. Awesome

[nourathar]

!

[quantalume]

I ordered enough parts today to build 3 boards (got the ATmegas on eBay). Should have everything in hand by the end of the month, including PCBs. I'll probably only use two of them, so I'll have an extra complete kit available if someone is interested (will sell at cost).

[nourathar]

makes me curious how many of these have now been built !
I suppose xwhatsit knows how many pcb's have been produced in total..

When I'm done I will have at least one spare to sell too !

[xwhatsit]

I think there's been a paltry 12 produced by me.

On a positive note, on Monday I submitted the Rev4 PCB for manufacture. In a couple of weeks I hope to have my hands on some tasty fresh boards.

Let's see if OSHPark allows hotlinking...

Top:

Bottom:


Key changes:

• 6-pin header (top left, marked P2): breaks out 5V, GND, and four GPIO pins. This will allow LEDs (if you're mindless enough to drill holes in your beamspring), and also (yay!) connection to a solenoid driver board (which I haven't designed yet; it will need 10V boost converter in it to drive the solenoid effectively)
• Shift to tiny 74AHC595 DHVQFN16 shift registers for column drive. Detailed a page or two ago. More drive, smaller package, lets me keep a much tidier layout and leave more of the bottom side for a solid(ish) ground plane
• All components on top side. Makes assembly much easier; do it one hit in a toaster oven, or allows hotplate/skillet reflow (Sparkfun style)
• Big ugly logo (to match my other projects)

I contemplated going to USB micro, as USB mini is technically deprecated. However there's such a bewildering variety of USB micro connector styles, that if anybody else wanted to take the existing PCB layout and produce it to assemble their own, they might struggle to source the exact same connector that I designed the board around. For now I think USB mini is acceptable.

The ATmega32U2 shortage is a pain. I don't know who ordered them all up! Clearly not the keyboard converter cottage industry For now I have taken a risk and ordered six from a Canadian seller on eBay. He seems to have good feedback... hope they're legit chips! Never bought ICs from eBay before.