H3 port extender, extra USB and RS-232 ports

[mctom]

Compared to my previous desktop PC, H3+ lacks only one thing - a true RS-232 port, that I need for my thermal printer.
And then I discovered the truth about the H3 GPIO header - three extra USB ports, and UART port. Just what I need!

So I designed this board:
- 2x USB 2.0
- 1x actual RS-232 (with MAX3232 or SN75C3232E if someone needs 1Mbps)
- A 4-pin header for the official power switch (optional resistor R1 to dim it)
- Soldering pads with remaining I2C ports.

The board has 37mm height and 40mm width, so may need a diet to fit into a reasonable case. This certainly can be done.

Normally I try not to brag about projects in progress, because everyone knows what often happens to projects, but!
This time I'd like to probe the market demand for it - if that's just me, I can take some liberties in one-off design.
Conversely, bulk orders are cheaper.

I also started drawing the same board, but with 10-pin IDC connectors, one for USB and another for RS-232, as often found on PC motherboards. And what do you know, they actually take more space than the actual USB connectors, so I don't know if I'll continue that effort. Maybe tomorrow

So, feel free to share your thoughts - not only the design (which I admit needs some.. polishing), but about the concept as well.

[mctom]

Placeholder for the actual end result, if it ever happens!

[odroid]

Very nice and practical design.

[mctom]

I have identified a problem with the previous design - it is very impractical to guarantee that both USB and DB-9 ports would be of comparable height.
The USB ports are no problem, as I have selected a quite reputable manufacturer Molex, so their dimensions are very well specified.

I also grew confident that RS-232 ports are abundant online with a IDC-10 cable, that can be easily adjusted by a user to a desired length. This is not exactly true with similar solutions for USB2 ports, that usually have individual wires.
This means I can place RS-232 port on the back, and extra three USB ports on the side. If someone is not interested in RS-232 port that is completely optional, just like USBs. I think I have achieved a truly customizable design, at last.
By the way, we call this thing "herring" in Polish.

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I preserved the 4-pin connector for the power button, but changed its form to dual-row. I got rid of I2C pads, as if someone wishes to use them, it is always possible to solder wires directly to the 24-pin socket pads.
I also added ESD protection to USB ports. ESD protection of RS-232 port is guaranteed by underlying voltage translator.
An extra M3 hole is there for fixing the module to the side wall of the case, so the user won't push the module inside with a reversed pendrive.

Now I am more confident this is feasible to incorporate into a 3D-printed case design.

EDIT: The new dimensions are 31.75mm width, 37.5mm height.

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[hominoid]

Nice project, I could use one for sure. You made me open up my H3 again to take a closer look at the clearance...it's close. The fan connector is right there but it looks like the serial header will pass behind it, alongside the heatsink. How about using a Qwiic JST SH 4-pin for the I2C, top corner above the USB on either side, maybe. It would be nice to have easy access to the I2C and it could be left unpopulated.

Regarding mounting in a case, the header mount with side wall access is nice. One hole and a standoff and your set. With a second hole on the PCB, it could be mounted remotely in another location using a ribbon cable. That might be beneficial for larger cases or for moving the USB to a different face and, some mount flexibility would be a nice bonus. Height wise, with a 2mm wall thickness, the minimum shell case top is 40mm tall so 38mm inside clearance. Subtract 2mm for the header height and another 1mm for pad, solder and tolerance and it's at 35mm. With your current design it's very doable with a modest increase of 2.5mm from the minimum enclosed case height.

[mctom]

Thanks for your input, @hominoid.

You made me open up my H3 again to take a closer look at the clearance...it's close. The fan connector is right there but it looks like the serial header will pass behind it, alongside the heatsink.

Fortunately I didn't have to open up my H3, my work is based on the official photos.
After the design is finished, I hope to verify mechanical compliance using 3D model of this board and your H3 model.

How about using a Qwiic JST SH 4-pin for the I2C, top corner above the USB on either side, maybe. It would be nice to have easy access to the I2C and it could be left unpopulated.

That is an excellent idea. If I find SMD connectors of that kind, I'll place both at the unused space at the bottom, next to U1 chip.
That may be not the most convenient spot for the user, but will cause much less routing and signal integrity issues. In the essence I need to avoid routing anything near USB pairs.
Fortunately no pull-up resistor placeholders are necessary.

With a second hole on the PCB, it could be mounted remotely in another location using a ribbon cable.

Also a good point. "Remote mode" implies a 24-pin straight header on the another side of the PCB instead. I'll have to carefully analyze the pin order, I've seen too many boards with mirrored connector screw-ups. At the first glance it seems that should work without any modifications whatsoever.
I'll see if I can squeeze in another hole somewhere. Perhaps at the center of the bottom end, which won't be obstructed when straight pin header is in use.

For this reason and the possibility of reducing total height even further (by 2.5mm maybe), I was thinking about M2.5 or even M2 screw holes instead, but I can't tell whether inserts smaller than M3 are available and practical. I do know there are M2.5 standoffs in many sizes.

I could use one for sure.

We'll arrange that once the design is finished.

So my takeaway is:
- Add I2C Qwiic jacks
- Add mounting hole on the bottom
- See what can be done about the back side straight pin header (it should mate with IDC plug after all)
- Try decreasing the total height to 35mm (no pressure though)
- Carry on routing this thing.

[mctom]

So here's the iteration of the day.

I confirmed that in fact both right-angled female header, as well as straight male header on the bottom side, can in fact share the same footprint. A lucky coincidence, and how fortunate!
I decided against full fledged IDC-24 jack as it won't fit in there, but I think the standard pin header will be compatible with the plug.

I added 2x JST_SH_SM04B-SRSS-TB, which is a Qwiik-compatible jack. I couldn't find a 3D model in either step or wrl format, so there are only placeholder pads for now. I couldn't fit two next to each other, so one eventually landed on the top of the board, with traces between USB ports.
The I2C0's entry side is on top of the board, which makes it unusable in the minimal case, but I don't see it as a deal breaker.

Added another M3 hole on the bottom, looks fine to me.

I reduced the size of the board, now it's 35.3mm in height and 33mm width. BUT measured from the top of the board to the bottom end of an angled connector we've got 35mm almost spot on. Some 0.3mm is expected to extend below to fit some electronic components that otherwise wouldn't.

The distance between USB ports has been increased slightly.

[hominoid]

All goals reached, It's beautiful. I can't think of anything else to do right now, nice work.

[mctom]

Polishing it now before imminent PCB production.

I wanted to add a current limit for USB 5V bus just in case, in the end I added 500mA polyfuse. Will it be enough? Who knows.
I may replace it with a dedicated current limiting power switch that is always on, for the peace of mind. Not that we've got any GPIO to actually control that switch.

[odroid]

I think a load switch something like this one might be more economical as well as more reliable than a polyfuse. The response time of the polyfuse must be much slower.
https://www.lcsc.com/product-detail/Pow ... 76957.html

[mctom]

I think a load switch something like this one might be more economical as well as more reliable than a polyfuse. The response time of the polyfuse must be much slower.
https://www.lcsc.com/product-detail/Pow ... 76957.html

Yes, I guess polyfuses aren't quick enough to protect anything.

Yesterday I tried adding this:
https://www.ti.com/lit/ds/symlink/tpd3s014-q1.pdf
It's a SOT23-5 chip with both power switch and current limit, and ESD protection for data lines, all in one. But I couldn't find a way to route it on a 2-layer board and keep the traces laid out reasonably.

I think I'll update the PCB to 4 layers. Not only I have trouble routing these protection chips, I don't feel confident the USB data link will work reliably with wrong impedance. Probably would work with a keyboard or a mouse in low speed mode (1.5Mbps) but someone might want to use it with 5BK, card reader or a pendrive.

[mctom]

In the end I added TPD3S014, an integrated data pin ESD protector and power switch / current limiter.
I have published my work on github:
https://github.com/tomek-szczesny/odroid_h3_extra_ports

The IC placement under the port is tight, but it must be near the connector. Can't get closer than that

No dimensions or critical component placement has changed.

[hominoid]

I'm glad this is moving forward, I'd like to make one as soon as possible. I would make it a four layer board, it shouldn't add too significantly to the cost.

[mctom]

I'm glad this is moving forward, I'd like to make one as soon as possible. I would make it a four layer board, it shouldn't add too significantly to the cost.

Since the design is ready unless someone vetoes it, I'm going to order those PCBs and components next week. I have a deal with some dude that sources PCBs with free shipping.
I planned to send you 2 pcs all along with SMD assembled and THT bundled, so if all goes well you should get them by the end of a year.

If that doesn't work for you, let me know which PCB manufacturer do you prefer, and I'll make a spin-off design tailored to another 4-layer stackup.

I do hope to see it in SBC Case Builder someday.

[hominoid]

Wow, I'm good with that plan. Once you know the total cost send me a pm. You know that's why I want two, so I can add both styles to SBC Case Builder.

[mctom]

Wow, I'm good with that plan. Once you know the total cost send me a pm. You know that's why I want two, so I can add both styles to SBC Case Builder.

Good, because I'll be much more comfortable if I got a chance to test this board before it gets anywhere.

[mctom]

Being forced to disassemble my unit today, I took a closer look at the space available around the header.
The final result being: there is approximately zero space behind the module. The RS232 connector won't fit where it is now.
Fortunately I got a few days to fix this issue before it is too late.

[mctom]

If you can read this post, that means I'm not dreaming and indeed I connected my keyboard and mouse via H3 port extender PCB.
AND I turned on H3 with an official power button.

The board is designed so it may be mounted in two different ways:
- "Header Mount", Fitted directly onto a 24-pin header with a female socket (as pictured below)
- "Remote Mount", Bolted to a case wall with two M3 screws, and connected with H3 header with a 24-pin IDC ribbon cable.

Unfortunately, due to my poor spatial judgement, the RS-232 functionality will not be available when H3 Port Extender is mounted directly on the 24-pin header. The 10-pin IDC port won't fit on the back of PCB, and there's no room to move it on front - and no time nor resources to redesign the PCB.
The direct fit onto the pin header does not provide enough mechanical stability to connect and remove USB devices safely. The risk factor is the module touching the H3 heat sink while wrestling with a USB receptacle. The module must be bolted to a wall in a dedicated case for everyday use.

[mad_ady]

It looks very neat! So -- can't you stuff some filling (like a rubber gasket) between the PCB and the heatsink - to provide resistence against pushing?

[mctom]

Well yeah I could, probably. But I'll need a new case for this anyway, so why bother.

Got 3 spare PCBs if anyone's interested.

[hominoid]

Nice to see you have a board up and running. To bad on the serial port but I personally have no use for one, it might be useful to others. I cloned your repository and could not find a way to get the whole design as a 3D model. As you know it only exports the PCB and USB connectors. I pulled component models for the missing parts to make a more complete model.

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It looks like the component selection for the 24 pin header will be important because of the difference in width between manufacturers. In worst case the connector side next to the PCB hole may need to be trimmed and or a smaller standoff used.

In the future one possible solution for those wanting a GPIO header mounted serial port would be to swap components(header and IC’s) sides on the bottom. Or better yet, move the IC’s up so the 24 pin header can be used on either side.

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This allows for enough room for the enclosed serial header and extra clearance on the back. The plastic housing of the USB header would also prevent an accidental short by the heatsink. The additional protrusion of the USB ports can be accommodated by extra case width on that side. The downside is that it won’t work with existing cases but they wouldn’t have USB openings either.

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I haven’t order the 24 pin header yet so I’ll let you know if I find something that works better then the others. I also need to validate the location of the GPIO header on the H3 once I get a PCB so we know the modeling is accurate. SBC_Case_Builder main has been updated with the port extender model under h3_ultimate but neither are finished yet.

[mctom]

Nice to see you having the model almost ready by now

It looks like the component selection for the 24 pin header will be important because of the difference in width between manufacturers. In worst case the connector side next to the PCB hole may need to be trimmed and or a smaller standoff used.

I think your model of 24-pin female connector is unusually big. It looks like an IDC connector with a plastic keying tab on the front that fits male IDC headers.
Normally those angled female 2.54mm connectors should be about the same size as the male header on H3, which was true in my case and any other I've seen so far. I wouldn't worry about that.

Or better yet, move the IC’s up so the 24 pin header can be used on either side.

This would not work because the pin rows would be swapped. :/

However I'm considering a change in 4-pin power button connector - in Remote Mode I think it makes more sense to mount it on a back side, so only USB ports are on the front (and some THT pins).


I have already built two more boards, for Header and Remote mount. I'll give them a scrub and a test tomorrow.
I'm especially interested in pendrive speed / stability test through a ribbon cable.

[ChriO]

]Hi Tom
I would be interested in one PCB if still available. I sent you, well, tried, a personal message, is still in my Outbox. Dunno if I have to do anything or it will be really sent to you.
A dumb question, why not move the header connector to the back of the PCB, in other words, move PCB away from the heat-sink. In my type-3 enclosure there enough space. And if you would "stretch" the PCB to the right
you would have USB connectors in the "window" of this side of enclosure.
I made a primitive extenssion using prototyping board and lots of soldering, placed it in this window and fixed with four small screws. Works OK. You don't want to see the backside of it

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[mctom]

Hi,

Sure, I'll send one PCB your way.
Your message was in Outbox until I read it, that's normal on every forum with phpBB engine.

The point of this design was to keep it as compact as possible. These days everyone wants stuff smaller than it should be.. And H3+ Port Extender was no exception.
In fact, there was no reason to make it larger, except me trying to squeeze in more connectors on the back - that attempt did fail indeed.
But no worries, tomorrow I'll make some additional tests with ribbon cable and see if the Port Extender works remotely - unfortunately I had no 24-pin IDC connectors at hand.

I own Type 2 case and had no idea Type 3 has a window that couls be used - I suspect its purpose was to provide adequate ventilation to the heatsink. Keep an eye on the CPU temperature with that!

[hominoid]

In fact, there was no reason to make it larger, except me trying to squeeze in more connectors on the back - that attempt did fail indeed.

I wouldn't call it a failure, the ribbon cable can be soldered to the board to use the serial port.

[mad_ady]

@ChrisO I like how you reused the hole in the type3 case! But yes, I get a nice, warm, hand warming air flow from there

[ChriO]

@mad_ady, You must be using Gentoo Linux or compiling the kernel all day or there is much warmer there in Romania than here in Poland or all this together
I don't even use (yet) a fan and the box is not much warmer than the ambient temp.
And just in case, there are plenty of space to make additional holes if necessary.

[mad_ady]

I'm on BIOS 1.09 (which lacks some c-states), in unlimited power mode (my h3 doubles as a gaming rig as well ), so the fan starts rather frequently.

[mctom]

Finally, some results!

I got the 24-pin IDC connectors from TME and made a 12" remote connection of Extender Board with H3+.

The USB still works! :O

I attached an old Kingston pendrive (Certainly USB 2.0) and copied a ~4GB compressed file back and forth:
To pendrive: 22.79MB/s (approx.)
From pendrive: 22.96MB/s.

The first figure is the lowest given by mc at the end of copying, and the second is file size divided by execution time of cp.
I had no better ideas how to test this reliably.

But anyway, I will never recommend these ports for reliable and fast data transmission. The point is to provide ports for stuff like keyboard, mouse, Arduino, legacy interfaces and so on.
The main reason being, those ribbon cables have nothing to do with the correct differential impedance as required by USB standard. It will be good enough for mostly anything that doesn't require sheer speed.

I also tested a RS-232 port with my thermal printer and it works just fine too. A graphical print with no single pixel error.

It looks like the component selection for the 24 pin header will be important because of the difference in width between manufacturers. In worst case the connector side next to the PCB hole may need to be trimmed and or a smaller standoff used.

I think your model of 24-pin female connector is unusually big. It looks like an IDC connector with a plastic keying tab on the front that fits male IDC headers.

Your observation was correct nevertheless, I did have to remove the standoff to fit the IDC connector on H3+ header. The Case 2 is still rigid without it, but I'm afraid your case design will have to account for that.. somehow..

My girlfriend approves of all this, which is also weird given how much time I've spent on it

[hominoid]

Good to see the remote mount is working. I have an idea or two regarding the close quarters at the header. I'll have to dig up a 24 pin cable and give them a try. Once I get setup I'll try the Qwiic connectors as well.

[blazini36]

Just so happens I just designed a pretty similar add in for RS232 only and the power switch. I need isolation from nasty environments so I'm using a fairly expensive chip, but I've used the max3232 quite a bit.

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[mctom]

So I see you board is mounted differently than mine, with LEDs facing the H3 heat sink. At least it will all fit, and not just barely.

And I suppose you skipped RTS/CTS?

[blazini36]

No, it's mounted the same way yours is. I just didn't alter the pinsocket footprint to reverse the pin numbers. I'm still playing with the layout which I can already tell is taller than I'd like

An no, I'm not using RTS/CTS, I have yet to find anything that uses them in the field. This chip only has 1 transceiver unlike the Max232 which has 2 where 1 can be repurposed as a CTS/RTS.

This isn't a "for everybody" design, my H2/H3s live inside electrical enclosures mounted to DIN rail. I just need a good RS232 port for legacy stuff.

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[mctom]

I see, so no problem with left hand side spacer either, as seen on the first photo here:
viewtopic.php?p=362389#p362389

Also I see you have a H2 3D model, in H3 the fan socket is closer to pin header. Not a problem in case of your design though.

[blazini36]

No I don't care about the standoffs, My H2/H3s live like this...

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Resolved that anyway, at least in the case of the H3 when I reworked it to shorten it so it's not flapping in the breeze

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[mctom]

Never though I'd brag about that, but I think mine is still smaller than yours
But I'm guessing you want to keep all the components on top for simplicity. Also, 2 layers will make it cheaper.

That a busy looking H3 and a cute companion for it.

[hominoid]

I recently received my port extender boards, a header and remote mount. They both look great and should do the job very nicely. I was looking at ways of mounting the remote version and came up with a simple solution that’s sturdy, exposes all the connections and is easy to implement. I’m using it in SBC Case Builder but it works by itself and could even be hand fabricated.

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Either holder piece can be used to secure the top of the header mounted version too, depending on if the serial or power switch headers are installed. I’ve included the source so the offset to the wall and USB depth can be changed for any case design. A bezel could also be used to countersink or recess the screws, strengthen the front and provide an esthetic value.

h3_port_extender_holder.scad.zip

(1004 Bytes) Downloaded 5 times

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[hominoid]

I used @mctom’s case design called h3_ultimate2 as a test case for the remote mount. The design is a side vented case using a 60mm fan with a nice hex vent grill on the opposing side that is easily removable for access to the SATA connectors. It use the HK power switch, has a mount opening for a serial DB9 connector in the rear and three USB in the front. I like this case and it’s a nice size, good design job.

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@mctom's case design h3_ultimate2 is available on the main branch of SBC Case Builder.