"Porcupine" Breakout Board

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"Porcupine" Breakout Board

Postby FHuettig » Thu Jun 19, 2014 9:38 am

Hi all,

At last I have a breakout board nearly ready for fab., please review and comment here. I know it can't be everything to everybody, I already had to pare it down from a more complicated original concept which is part of the reason I haven't gotten it out sooner. The goals in design were:

  • Fit in the same outline as the Parallella, with the same mounting holes to support stacking.
  • Minimum # of layers to keep the fab cost down (6).
  • Provide an easy way to chain boards together with mass-terminated ribbon cable. It may not support the maximum data rate, but should still be useful.
  • Allow use with simple breadboards by keeping all GPIO & power connections on a 0.1" grid.
  • Allow connection of simple peripherals like UART or I2C with 3- or 4- pin connectors & cables.
  • At least one PMOD connector (I only had room for one, but it's a 12-pin dual-row PMOD).
  • Standard Xilinx JTAG connector.
  • Support power-consumption characterization.
  • Should also be a good template for creation of other daughtercards.

I've attached a PDF of the schematic, and some 3D images from KiCad (I -really- like that feature!). Beware that the 3D model of the PMOD connector is not correct, the actual connector will extend to the edge of the board. The full project, plus a "paracard" template, is available on the github repo here.

I'm aware that the differential routing on the eLinks is not great, the pairs are loosely coupled at best and are not length-matched especially between pairs, but the overall lengths are pretty short and I expect this will not limit performance compared to what we can get through a standard 1mm-pitch ribbon cable.

porcupine_front_oblique.png
Front View, Oblique
porcupine_front_oblique.png (84.98 KiB) Viewed 26845 times


This one shows the signal "hints" on the silkscreen:
porcupine_front.png
Head-on view.
porcupine_front.png (38.84 KiB) Viewed 26845 times


The back view shows the Samtec connectors:
porcupine_back.png
Back view
porcupine_back.png (76.55 KiB) Viewed 26845 times
Attachments
porcupine_sch_UNRELEASED.zip
Schematic for "Porcupine" breakout board.
(945.66 KiB) Downloaded 691 times
-- Fred -- Hardware Guy --
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Re: "Porcupine" Breakout Board

Postby shodruk » Thu Jun 19, 2014 11:09 am

Wooooooohoooooo!! :D :D :D When? How much?
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Re: "Porcupine" Breakout Board

Postby 9600 » Thu Jun 19, 2014 2:30 pm

Looks pretty great to me, Fred. Can't wait to get a couple and start experimenting!

Cheers,

Andrew
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Re: "Porcupine" Breakout Board

Postby bithead » Thu Jun 19, 2014 5:13 pm

Would it be too meta if someone starts a Kickstarter campaign to fund an accessory for an item that originated as a Kickstarter campaign?
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Re: "Porcupine" Breakout Board

Postby FHuettig » Thu Jun 19, 2014 7:16 pm

:D It would be meta, but not as meta as this! :lol:
I think we can handle this one, I'll let everyone know when these will be in the shop and for how much.
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Re: "Porcupine" Breakout Board

Postby timpart » Fri Jun 20, 2014 12:25 pm

Looks good.
On the silkscreen for the GPIO could you put signal numbers next to all the pins please. They are arranged differently from the PEC and V and ground have moved so I think it could avoid confusion, and late night miscounting of pins when making connections.

Add a version number next to word Porcupine.

Perhaps some kind of open hardware logo as well?

From the circuit point of view is there a track from the power mounting holes to say a hole which something could be soldered into?

Is there somewhere a fan could be soldered in?

Thanks,

Tim
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Re: "Porcupine" Breakout Board

Postby 9600 » Fri Jun 20, 2014 1:08 pm

timpart wrote:From the circuit point of view is there a track from the power mounting holes to say a hole which something could be soldered into?

Is there somewhere a fan could be soldered in?


I think it's best to avoid direct soldering wires, even when you are putting something into an enclosure, as there always comes the time when it needs dismantling and you end up with wires in the way and getting twisted and pulled.

There looks to be a pair of pins with 5V and GND next to top-left mounting hole, and I guess if there were room, it me be nice to have a 2nd pair.

Best,

Andrew
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Re: "Porcupine" Breakout Board

Postby timpart » Fri Jun 20, 2014 6:28 pm

9600 wrote:
timpart wrote:From the circuit point of view is there a track from the power mounting holes to say a hole which something could be soldered into?

Is there somewhere a fan could be soldered in?


I think it's best to avoid direct soldering wires, even when you are putting something into an enclosure, as there always comes the time when it needs dismantling and you end up with wires in the way and getting twisted and pulled.

There looks to be a pair of pins with 5V and GND next to top-left mounting hole, and I guess if there were room, it me be nice to have a 2nd pair.


Sorry, was a bit rushed. I was thinking of holes where we could add some extra headers ourselves If we wanted to. Keeps the component cost down for Adapteva, but doesn't add much to board cost. I have no clear idea of board economics, so could be wrong here.

If someone wants to override the the X and Y position of the board is it acceptable to connect those wires directly to 0V or
1.8V? The parallella connects them via resistors, but I'm guessing that is so they can be overridden. If it is OK to directly connect then making 1.8V available on two more pins on an extended J2 header would be useful.

Tim
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Re: "Porcupine" Breakout Board

Postby FHuettig » Sat Jun 21, 2014 12:40 am

timpart wrote:Looks good.

Thanks!

timpart wrote:On the silkscreen for the GPIO could you put signal numbers next to all the pins please. They are arranged differently from the PEC and V and ground have moved so I think it could avoid confusion, and late night miscounting of pins when making connections.


I did have the power and ground marked V and G, I was waffling on numbering the other signals because their definitions can change depending on the FPGA configuration. For example the schematic shows the differential numbering which simply goes in order by pair. However when I made the single-ended FPGA configuration I renumbered them to make the order "clean" on the PEC, so while the GPIO_P0 and GPIO_N0 are on one side of the PEC with GPIO_P1 and GPIO_N1 on the other, the single-ended ordering resolves to an odd side and an even side on the PEC. It made sense at the time, but then I wanted to set these 0.1" headers up so they could be used for differential signaling, say with twisted-pair ribbon cable, so you'll see all the Ps are on one side and all the Ns on the other, which scrambles the ordering for the single-ended signals. It's described in the schematic and now I've carried those numbers to the silkscreen as well. I agree that late at night it's best to have some landmarks, even if you have to make notes of which ones are which. I wasn't able to fit the numbers on the bottom side of the GPIOB connector (J7) because of the notes related to J2, but the bottom row is always the top row + 2.

timpart wrote:Add a version number next to word Porcupine.
Perhaps some kind of open hardware logo as well?

Done and done, the first was on my list of clean-up items anyway, but it was a nice idea to add the OSHW logo too. Here's an image with the new silkscreen:
porcupine_newlegend.png
New legend
porcupine_newlegend.png (33.5 KiB) Viewed 26402 times


timpart wrote:From the circuit point of view is there a track from the power mounting holes to say a hole which something could be soldered into? Is there somewhere a fan could be soldered in?

The 2-pin header at the top-left corner (It's J4, but for some reason the reference designators don't show up on KiCad's 3D plots!??) is connected to the "Power" mounting hole, it can be used to get some power in or out if using the powered-mounting-hole feature. Also, the POWER_PEC header block at the bottom-left (J3) will normally NOT be installed because I think of that as mostly only useful for power-consumption characterization and don't expect many people to do that. We don't want people to be pulling much current from any of the Parallella's rails (citation needed, or an app note maybe). That footprint has two 5V pins with adjacent grounds, so it would be easy to add a two or four pin header there and use it for fans or anything else. I intended it that way at least.

timpart wrote:If someone wants to override the the X and Y position of the board is it acceptable to connect those wires directly to 0V or
1.8V? The parallella connects them via resistors, but I'm guessing that is so they can be overridden. If it is OK to directly connect then making 1.8V available on two more pins on an extended J2 header would be useful.


Yes, that is another intended use for this board. On the parallella those pins are either pulled up to 1.8V via 4.75k or to ground via 1k, so forcing a pin with a direct connection is no problem. Initially I had a three-row header so you could set any address by placing jumpers, but that took up too much room and made the board look cluttered, so those pins became part of a larger J2. J2 already has both 1.8V (pin 21, adjacent to the X/Y pins) and several grounds available. Note J2 already has "reminders" next to each pin on the silkscreen.

The board is now out for fab, I'll have it back in a week!
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Re: "Porcupine" Breakout Board

Postby nutpoasa » Sat Jun 28, 2014 5:51 am

Wow! Your board looks awesome! I just drew up a breakout board, created the Gerbers and went to try and order the Samtec connectors but can not find them for sale. Where did/do you purchase them?
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