RP2040 Expansion Card

Any suggestions before I send this off for manufacturing? There will be a NeoPixel but I’m yet to decide sizing/package on GPIO25

Just for some additional context, this will have two parts, the expansion card and then the add-on boards, which is why there is that board-to-board connector.

@Josh_Cook

oh wow I just finished designing my own. would have be really glad to see your post sooner.

Disclaimer: I am quite new to pcb design let alone working with rp2040. There are most certainly dumb things in the layout. Be kind to it :slight_smile:

I made one in a single 2 layer pcb with 2.54 pitch headers integreated in module (tbh it is 2mm longer but lets not talk about that). Needless to say, compromises had to be made.

  • no leds, figured I cannot see it anyway (but can be added by using solderpads)
  • I have 20 pin out with 2 ground because I figured I won’t need more than that amount of IO
    • 8 more GPIOs and SWD port are available on pcb as solder pads
  • I have cheaped out on those filtering capacitors since it is just impossible to stuff them in there when I am using 0603 package for the ease of assembly. I boubt this will lead to any issue but testing definitely needed

Schematic

Layout



Update 2023-05-26

I just assembled one yesterday, it is not working but I think my solder job is the reason to blame. It was not showing up in dmesg (like you just need a pull up on d+/d- for a usb device to show up there) so I think the working condition of rp2040 isn’t met (lacking of power or crystal signal, probably). Will try to working on this over weekend but no promise made.

A photo of it

Also, current BOM cost is around $4.55 each and a realistic budget would be around $120 for 15 units. BOM is available here

Quick Update: nevermind just figured it out, used a wrong footprint for crystal. will fix & test that later

5 Likes

I’m at a very small 22mm x 26mm PCB, without the connectors it’s only 15x26mm, so a very small form factor, with 29 GPIO and a Neopixel and around 700mA on the 3.3V rail and ESD protection all exposed to a 32 pin header.

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the amount of stuff you crammed in there is very impressive. However, I would not want to assemble this my self since I imagine it is 0402 sized component all over the place. Unless you put most smd component on one side then it can be done with a hot plate

Would you plan to sell assembled units? I would be really interested
Also, if you don’t mind, please release the layout and BOM.

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Just chiming in, I’d be interested in purchasing a couple as well if anyone does a small batch production run.

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Nice work! Impressive routing job. Can you explain to me the air wires around the USB-C cutout? Are those routing signals on the board, or between the board and USB-C connector?

I love these RP-2040 projects, for someone who does a lot of development, or on the move, for RP-2040 they’d be a lot more convenient than a Pico.

@Kris_Keillor They exist since I am using a usbc breakout board instead of a smd usbc plug which i admittedly should have

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Finally got around to reviving this, but I’ve just finished validating my 1st unit.
Selling these for $30AUD here, excluding shipping and duties/taxes (EU only) which will all be collected at checkout.
These will come with 16MB of flash and all 30 GPIO are exposed + 5V and 3V3 along with the BOOTSEL and RESET buttons through a hole in the enclosure. The enclosure is open for the photo but will have a top snap-fit cover.

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Neat! Shipping is kinda expensive to Germany, I guess I’ll ask around in the local hackspace if someone else wants anything.

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@Josh_Cook I just tried to make an order and it’s not letting me place my order; it says

Unfortunately one or more items in your cart can’t be shipped to your location. Please choose a different delivery address.

I’m very confused, since I’m in NSW, and from your post you seem to be in Australia as well, so I don’t see any reason shipping shouldn’t be possible.

Do you know what’s going on?

I’m aware of this issue and working on a solution.

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The issue has been fixed, I’ve also added a failover rate in case this happens at $11, but if you do see it, I’ll refund you the difference between what I paid and what you were charged.

Would be interested in getting one (I’m also from Germany)

This is sweet!