P2D2 - An open hardware reference design for the P2 CPU

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  • @cluso99 - LCSC have stacks of them, and at the right price. I am getting 40 way sockets but they also have 50 way which might be useful because I extended the 50mil pins to 43 in each row to accommodate the C2 programming pins once the 100mil are chopped off. Do they cut down cleanly?
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-01 - 07:24:17
    To complement the P2D2 50mil header I am also making up a 50mil prototyping matrix board which the slim P2D2 can plug into with its dual 40-way 50mil headers on the board. Another advantage of this is that it allows for SOIC and even modules like the ESP32 that can solder directly to this matrix board.

    Of course it will be all plated-through and I am just checking cost for enig or hasl etc. The size I'm working with at the moment is the same as some other matrix board I have which is 2.75" x 3.75" although I will look at larger sizes as well since you can always cut them up. I'm not worried about mounting holes because they use up space and you end up cutting down anyway etc. Same too with ground tracks etc as I find it so easy just to run a bit of bare wire-wrap wire down the pads and around the bend etc for my rails, tacking it down with some solder as I go.

    Pads are 45mil square with 25mil hole and 6mil clearance.
  • jmgjmg Posts: 14,495
    To complement the P2D2 50mil header I am also making up a 50mil prototyping matrix board which the slim P2D2 can plug into with its dual 40-way 50mil headers on the board. Another advantage of this is that it allows for SOIC and even modules like the ESP32 that can solder directly to this matrix board.

    Of course it will be all plated-through and I am just checking cost for enig or hasl etc. The size I'm working with at the moment is the same as some other matrix board I have which is 2.75" x 3.75" although I will look at larger sizes as well since you can always cut them up. I'm not worried about mounting holes because they use up space and you end up cutting down anyway etc. Same too with ground tracks etc as I find it so easy just to run a bit of bare wire-wrap wire down the pads and around the bend etc for my rails, tacking it down with some solder as I go.

    Pads are 45mil square with 25mil hole and 6mil clearance.
    45 + 6 does not add to 50 ?

    It can help with these small pads, to make them rectangular/oval, rather than square, as that gives more strength and makes soldering easier.
    We have even done offset ovals on such smaller parts.
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-01 - 08:18:17
    Well 45 + 5 seeing that is all the clearance I need anyway, as lone as it passes the design rules etc.


    I've only just did one up to check to see if there was any premium for having that many holes but the jlcpcb bot says "nah, she's all good mate".
    Octagonal pads are just as good but I'm uming and ahring about whether to have 25mil holes or 35mil since they are pth. The larger holes will take 0.1" pin headers etc but leave less pad area, but being pth the solder will flow through anyway. Having smaller holes will mean less jiggle room for those 50mil strip headers and better soic mounting.
  • How about alternating? Gives you best of both worlds. So the 0.1" would just connect P0, P2, P4 etc, right?
  • jmgjmg Posts: 14,495
    ..
    Octagonal pads are just as good but I'm uming and ahring about whether to have 25mil holes or 35mil since they are pth. The larger holes will take 0.1" pin headers etc but leave less pad area,..
    If it was me, I'd stick with the right pad & hole for the connector, as there are already 0.1"headers that give all P2 pin access.
    Larger holes just cause wobble and alignment problems, and you want to avoid mechanical stress on plated holes.
  • Here's a photo of pyboard D which has the alternating holes, that keeps everything central
    https://blog.adafruit.com/2019/02/05/micropython-pyboardd-at-fosdem-micropython-micropython-fosdem-fosdem/
  • Tubular wrote: »
    Here's a photo of pyboard D which has the alternating holes, that keeps everything central
    https://blog.adafruit.com/2019/02/05/micropython-pyboardd-at-fosdem-micropython-micropython-fosdem-fosdem/
    It's an idea for sure but that board didn't have any headers soldered to it. Once you solder on the 100mil header then it is effectively locked into a crippled state. With 50mil socket on the P2D2 component side it would be mounted low-profile onto cheap pin headers but you still have the option of cutting the bottom of every odd pin on that header to make it fit into 100mil holes anyway, without making the change permanent on the P2D2 module.
  • jmgjmg Posts: 14,495
    Tubular wrote: »
    Here's a photo of pyboard D which has the alternating holes, that keeps everything central
    https://blog.adafruit.com/2019/02/05/micropython-pyboardd-at-fosdem-micropython-micropython-fosdem-fosdem/
    Interesting, I see they alternate pad sizes there too, to avoid annular rings vanishing.
    Hard to see, but do they also plate down the PCB edge too ?
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-02 - 00:09:45
    @jmg - they definitely look like some kind of castellations there.
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  • Not sure what you mean by plated edge, they are routed castellations, here's a pic

    Did you mean also plate the flat edge of the fibreglass?

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  • jmgjmg Posts: 14,495
    Tubular wrote: »
    Not sure what you mean by plated edge, they are routed castellations, here's a pic

    Yes, that's a much better photo, thanks.
    They have parts on both sides, so flush surface mounting of that will need a large cut-out, but even if it is not used that way, the edge plating (castellations) gives another redundant top-bottom connection, which is nice to have if you can get it for free....

  • @Peter Jakacki

    A quick question - have any P2D2 boards been delivered yet? I paid for one, but have completely lost track of what is happening with them.

    Ross.
  • RossH wrote: »
    @Peter Jakacki

    A quick question - have any P2D2 boards been delivered yet? I paid for one, but have completely lost track of what is happening with them.

    Ross.

    Same here. Hoping to get mine so I can get up to speed once I close the marina in mid October.
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-02 - 04:37:29
    After having sourced affordable 50mil headers I have added some extra pins to the 50mil strips for USB D+ D- and C2 programming for the USB chip. While doing all this I made up a matrix proto board as well and thinking about it I figure why would I bother with bulky 100mil header pins? If I cut down the P2D2 to the 50mil and add edge castellations on those 50mil through-holes like I saw on that pyboard, then I can smd the board without any cutting. The P2D2 could even be soldered directly to a pcb with pin headers straight through, or low profile and flipped as I intend to use it with 50mil sockets on the P2D2 component side and cheap pin headers on the pcb or matrix board.

    Where does that leave anyone who wants to use 100mil header pins? No problem, the P2D2 can attach to a 100mil header adapter, and there is no need to make these up since I already have hundreds of P2D2r4s which includes the RPi 40-pin header that the P2D2 can attach to. You can even solder down the adapter and plug in the P2D2 on the 50mil header in fact.

    There's also another adapter I am laying out that is basically a combination of the RPi HAT that takes a P2D2 on 50mil and also is populated with 50mil pads for prototyping through hole or smd.

    @RossH - very very soon!

    The pcb would be chopped just along the edge of the rectangular pads to expose the TH plating of the edge vias, thus castellate them.
    P2D2ED.png
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  • Hi Peter and all, don't run out of patience. To run out of patients is what we wish to others. Now we are so near to an end of an nightmare we never could imagine to happen, after all what we suffered in creating not the incredible things nobody has even heard of, we should just stay patient for some decades of decent days and the need will vanish like a miracle, like a flue, the Propeller P2 will be officially released, the P2D2 will be available included the PAL and there are two more boards to come, one even looks very presidential, just many holes with something around running circles and shining golden. But that golden shine comes not from the boards but is the reflection of the bright ideas, we The People have already created in the anticipation of this splended device. So keep calm and hope for a brighter future!
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-02 - 05:45:47
    Oh, I forgot about my P2 Pixie version which will I will include in this run of pcbs. Essentially the P2D2ed attaches to this and it has a HDMI or VGA connector down the right end near the regulators. So it's a slim trim P2 dongle that plugs directly into the monitor and the left end has the microUSB connector. I will allow for a USB-A underneath just to keep the whole package slim. Funny thing is that the P2PAL could probably simply have a break-away HDMI/VGA tab on its left side which ends up on the P2D2 right side. So I will look at that idea and that won't impact the P2PAL itself since I/O lines are free down that end and the P2PAL pcb could be unpopulated expect for HDMI if that's all we needed. But think about it, this tiny slimline P2 board that has ESP32, USB-C, HyperRAM, RTC, USB serial etc, and HDMI that fits into a dongle case that can be 3d printed.
  • @RossH - very very soon!

    Thanks Peter. I'm still interested in the add-on boards as well, but I haven't paid for those yet.

    Ross.
  • Cluso99Cluso99 Posts: 16,673
    edited 2020-09-02 - 06:49:18
    Much better design Peter :sunglasses:

    0.05" pitch can be handled by anyone making their own pcbs and allow those pcbs to be smaller.

    And I understand you already have (in hand) the breakout add-on pcbs to add the 0.1" pitch connectors including RPi to the sides if required ;)
  • It's becoming confusing and I don't want to complicate the idea any further but maybe if you go down the skinny P2D2 path some P2PAL variant (not necessarily every one) could have the 0.1 inch breakout connectors as "wings" that stick out and the P2D2 PCB is the narrower of the two (i.e. the reverse of the original design).
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-02 - 12:22:28
    Yes, I'm probably still going to make them for those that really want them. Part of the reason for saying skinny is the way to go is to elicit some response. I'm looking at adding just the two 40 pin headers on either side if I can get it vgrooved slightly so it is still strong but will snap when clamped and bent.
    But I'm stoked with the 50mil header version since the board was getting bigger with the rpi header too, and I had trouble sourcing low profile 100 mill headers wheres the 50mil are very low profile. Plus I have USB on the extended header so that I can still add an external connector too.

    I'm toying with adding a HDMI socket or plug to the end of the P2PAL board which turns it into a dongle PC. But this short piece will be easy to remove too. Let's see what happens.

    EDIT: Just checked on one-sided V-grooving but it might not be suitable. I want to avoid having to press guillotine pcbs just to remove unwanted connector strips but still having to be careful to castellate the holes for smd. I may have to get two types done then.
  • GregCGregC Posts: 15
    edited 2020-09-03 - 00:55:17
    Where does that leave anyone who wants to use 100mil header pins? No problem, the P2D2 can attach to a 100mil header adapter, and there is no need to make these up since I already have hundreds of P2D2r4s which includes the RPi 40-pin header that the P2D2 can attach to. You can even solder down the adapter and plug in the P2D2 on the 50mil header in fact.
    For what it's worth, I like the idea of a simpler/narrower P2D2 with just the 1.27mm connector holes. For using a P2D2 with my own PCB based projects I'd probably prefer to just use a pair of 1.27mm male/female headers to plug the P2D2 into my own PCB, to also allow potential for module removal / replacement. This would generally also be low-profile enough, without resorting to soldering-on flush via castellated edges. If I want some 100mil dual row headers for easier prototyping access, I'd happily just plug the narrower P2D2 module onto a 0.1" header breakout carrier board. :smile:

    I'd noted that every time I saw the wider P2D2 board images I kinda had that slight uneasy feeling that the extra board width with multiple header hole strips just didn't feel right, as did the idea of having to break-off those long edges (without causing "board flex" damage!).

    But that's just my tiny & insignificant 0.0001c thought. No intention to offend anyone who likes the added header rows!

    (ps. I just noticed that I'd mixed metric, imperial, and mil dimensions, all in the one paragraph above. LOL).
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-03 - 01:32:08
    @GregC - Feedback is what I'm looking for, so all of it is significant.




    Just talking to Ray (Cluso99) and he was looking at the row to row pitch which isn't on a 100mil grid, in fact it is 1045mil. If this plugs into 50mil matrix board as is then the 5mil is no problem but I would round up the pitch to 1050 before it is manufactured anyway. So Ray says with careless abandon "can ya get it down to 1 inch", and this is from the guy that made a 28pin DIP P1 by sawing a DIP40 chip! Well I can't chop off any P2 pins, and even though it is "only 50mil", it will be a lot of pain, but I will try anyway.

    Last night I searched for anything I could find about pcb manufacturing guidelines in regards to castellations. Although I know a bit more, I'm still not sure. It seems that I need to have 24mil min hole size (unless it is a special) and a certain clearance from pad to pad but I haven't found any guidance in regards to through hole pad + castellated pad. One of my old pcb fabs, Storm Circuits showed a board with through hole pad and a castellation on the edge of it, but as if both holes touched so that there was no material left between, or what looked like a thin wall. Not sure if I want that though.

    It seems that the pyboard that jmg referred to must have castellations with hole sizes less than 24mil, so it would be extra cost.

    In regards to imperial vs metric, I just use the simpler one such as "fifty mil" vs "one point two seven millimeter", or 1mm vs 39.37mil etc. But some people say "mil" when referring to "millimeters", and that's where it gets confusing. Btw, the old British term is "thou" pronounced like you are about to say "thousandth of a inch", but the American "mil" (milli inch) is easier to write and say.

    P.S. OT - when it comes to American vs British pronunciations/spelling, they both have their quirks, but I can never seem to get some Americans to say "solder" as it is written and as they would say other similar words such as in "old, older, cold, colder, sold, solder" :)
    They never hear that they actually say "sodder". I notice the letter L is dropped off a lot, as in "vulnerable" etc. A lot of Australians end up pronouncing it the American way "vunerable" from watching too much Hollywood :)
  • P.S. OT - when it comes to American vs British pronunciations/spelling, they both have their quirks, but I can never seem to get some Americans to say "solder" as it is written and as they would say other similar words such as in "old, older, cold, colder, sold, solder" :)
    They never hear that they actually say "sodder". I notice the letter L is dropped off a lot, as in "vulnerable" etc. A lot of Australians end up pronouncing it the American way "vunerable" from watching too much Hollywood :)

    Yeah I know the "solder" thing too and it's just weird. The first time I moved to Silicon Valley that hit me right away when I chatted with the PCB guys and they were saying that, and I would ask them to say the words "colder, folder, bolder, holder, solder" but only for the word solder would they skip the L. I still have no idea why they do that. But then again they did have a hard time understanding me too at first, especially the word air and tire/tyre, as us Aussies don't roll the "R" at all. I once went into a gas station there and asked if there was anywhere I could get some air for my car tyre . It probably sounded to them like "Can I get some ay-a for my kah ty-a?". The guy there simply looked at me in total confusion and couldn't understand a word until I figured I needed to emphasize those R's much more. Accents are strange/funny for everyone.
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-03 - 02:58:53
    Try asking for water - no idea what you are talking about. But this youtube helps :)


    @rogloh - give me a ring sometime about P2D2. I'll pm my number.

  • Cluso99Cluso99 Posts: 16,673
    edited 2020-09-03 - 03:43:04
    OT
    If you pronounce the T as D then why isn't it spelt wader?
    Then there's the a sound, so spell it worder or maybe wauder?

    Honestly, I don't know how anyone learns English. Pity help those who are not native English speaking :(

    Then there are the Kiwis with their fsh and chps.

    In Oz, we have Albany pronounced with "al" and Albury pronounced with "all", castle and carstle, vase and varse (notice the included r).

    Then we have one and won. It's just a mess, and it's the language trying to take over. I guess we don't have objects with gender like the French and Germans.

  • P.S. OT - when it comes to American vs British pronunciations/spelling, they both have their quirks, but I can never seem to get some Americans to say "solder" as it is written and as they would say other similar words such as in "old, older, cold, colder, sold, solder" :)
    They never hear that they actually say "sodder". I notice the letter L is dropped off a lot, as in "vulnerable" etc. A lot of Australians end up pronouncing it the American way "vunerable" from watching too much Hollywood :)

    It's because Americans speak a form of 18th century English, rather than the Queen's English:
    https://circuitspecialists.com/blog/solder-not-sodder-the-story-behind-the-silent-or-not-so-silent-l/
  • Peter JakackiPeter Jakacki Posts: 9,718
    edited 2020-09-03 - 14:33:22
    I've moved the 50mil header back to 1" row to row whereas before it was 1.045. Not much, but I had some work to get it back there and the castellations are 50mil out from there but I might move them closer once I find how close I can put them to the inside holes. So at present that means the pcb is 2.190" x 1.1" in a DIP88 50mil package :) You only need header pins for 40x2 but I have the extra 4 on one side to provide the USB D+/D- and also the factory C2 programming pins for the USB chip which is still USB programmable as a HID device if the C2D line is grounded. The extra 4 on the other side are basically uncommitted although I have allowed for a dual resnet to ground on 2 pins which might be handy for LEDs but otherwise unused. I will use 1mm thickness pcb instead of the regular 1.6mm since the module is so small.

    Here are the 3D gerber shots of the top and flipside where the P2PAL option goes. Now this pcb is tiny and just to give you an idea of how small it is I have an outline of a DIP40 next to the P2D2. In the same amount of space you have room for a DIP40 but not much else. I think I might even get a DIP40 adapter made up for this.

    P2D2ED%20vs%20DIP40-1.jpg

    P2D2ED-1.png
    P2D2ED-2.png
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  • Nice job Peter! Looks great beside that DIP40 :)
  • That's indeed a pure piece of art Peter!

    P2D2 looks to have matured very nicely. Can't wait to be able to pop the cork on one of these beauties and sample some of this P2 goodness for myself! :smile:

    I do suspect you could get the castellated edge closer in, but then again, that would detract from having a nice & tidy 50mil placement grid for host PCB layout.
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