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I recently designed a PCB, with a connector for an extension module for "future uses" (with various signals: GPIOs, I2C, SPI, USB2.0, USB3.1, PCIe Gen4).

The connectors are fine pitched (and OK for high speed signals). This means I can't connect them directly to a prototyping PCB (stripboard/veroboard).

So I was planning on doing a small "breakout" PCB (basically a stripboard attaching to the fine pitched connector) so that I can do some fast prototyping.

My question is what signals make sens to breakout on this stripboard, and which one wont be usable until I make a specific PCB:

  • GPIO, I2C and SPI should be fine (at least at reasonably low speeds)
  • PCIe will probably not work, so I will not include it (if I need PCIe, I will have to make a proper PCB for it, specific to the use-case)

But what about the USB connections? Is there a chance of them working (even in low speed mode: 1.5 Mbit/s) on a stripboard?

Is it useful if I do a 4 layer "stripboard" with a ground plane (full of holes) just bellow the "stripboard" layer?

So basically: is it worse the effort to add USB breakout on my "stripboard" module, or is it strictly mandatory to do a proper PCB?

PS: I know perfectly well that USB is supposed to be routed as a proper differential pair, with precise specifications. The question is just if one can do without it for some "quick and dirty" prototyping, to validate some concept before ordering a proper PCB.

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    \$\begingroup\$ So what do you intend to prototype that would connect to USB data wires? Usually, if you have say an MCU with USB, or USB UART chip, the USB data wires just would go straight to that chip. \$\endgroup\$
    – Justme
    Sep 19, 2023 at 9:18
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    \$\begingroup\$ "so that I can do some fast prototyping" -- Simple. Don't. Do it on copper clad (deadbug / Manhattan style / hand-carved with a utility blade or rotary tool) instead. \$\endgroup\$ Sep 19, 2023 at 9:20
  • \$\begingroup\$ @Jusme : for now, I don't intend to prototype anything with this breakout board (for now, it's only use will be to provide better testpoints for some signals I haven't mentioned yet because out of topic (ie be able to attach a scope probe without having to hold it). For now, I don't expect anything in particular, but I wouldn't be surprised if one day I'm asked for something requiring a MCU, or a USB to XXX converter (XXX being some protocol I haven't planed for, maybe RS485, or CAN, or ...). As I don't know the chip yet, it's hard to know where the USB wire would need to go. \$\endgroup\$
    – Sandro
    Sep 19, 2023 at 9:43
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    \$\begingroup\$ Keep the usb strips adjacent and as short and neat as possible and you'll likely have no problems for a prototype. \$\endgroup\$ Sep 19, 2023 at 9:46
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    \$\begingroup\$ Found Bit-Bang USB on MSP430G2452 which contains a picture of a project from M-atthias which implements USB 1.1 on a stripboard. That project uses a MCU without a USB controller and bit-bangs the USB 1.1 endpoint in software. The link is to an archived copy on the Wayback Machine as the original 43oh forum is down. \$\endgroup\$ Sep 19, 2023 at 22:44

2 Answers 2

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If you keep the USB strips adjacent and as short and neat as possible and you'll likely have no problems for a prototype.

For USB low speed, the 1.5Mbps is so low that you don't really need to put any effort into the routing. Even USB full speed at 12Mbps is pretty forgiving.

In terms of cable to board, cables with USB connectors on one end and 0.1" pitch headers on the other end are cheap and readily available, so that would solve trying to connect to the strip board.

Alternatively right-angle USB B connectors have a pitch and shape that it is possible to install them on strip board with a little care. From the image below, the 2.5mm pitch is close enough, holes can be drilled out for the 12.04mm mount spacing (close enough to 12.7mm) and the pins can be bent enough that the 2mm/2.71mm can become 2.54/2.54mm.

USB-B Connector Footprint Dimensions

From Wurth 61400416121 Datasheet

Even right-angle USB A connectors are close enough to be strip-board friendly.

USB-A Connector Footprint Dimensions

From Wurth 61400416021 Datasheet

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But what about the USB connections? Is there a chance of them working (even in low speed mode: 1.5 Mbit/s) on a stripboard?

USB 2.0 Data Rates & Timing

As you can see even Full Speed USB at 12 MB/s should be ok on a strip-board as long as you make en effort to keep all traces short and neat etc and keep maximum USB signal rise/fall times within the maximum recommended of not more than 20ns...

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