USB-C to DB9/RS-232

How many people would like a USB-C to DB9/RS-232/Serial expansion card as I have made a schematic for it? Pretty simple.


DB9 is nice but honestly I was looking at making an RJ-45 version pinned out so that you could use a regular Ethernet cable as a console cable to a network device console port (ala Cisco). I could see keeping both DB-9 and RJ-45 versions in the bag :slight_smile:

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Ah yes that would make sense to use Ethernet, but I do not really understand all the magnetics and requirements for Ethernet. I will work on the actual PCB soon, forgot to mention it has three small LED’s for RX,TX,PWR. Trying to get footprints and symbols is surprisingly hard. Using the USB-C plug that framework has does not have a shield pin which is required by specification. Are there any other plugs that would be useful?


Either one would be great, would be nice to keep a expansion cards in the bag when on site troubleshooting and issue with a Cisco router!


@Josh_Cook Sorry if I wasn’t making sense (it happens often!) I dont think the card should be talking the 802.3 Ethernet standard. It should be talking RS-232 via an RJ45 socket, pinned out so that when you use a TIA/EIA-568 (A or B) wired cable (i.e. Ethernet cable) with RJ45/8P8C connectors on the end, you can connect it directly to an RJ-45 serial port used by most of the common networking vendors (Cisco, Arista, Ubiquiti, Juniper, Palo Alto, etc.)

See below for common pinout for the RJ45.

If you understood what I said and meant something else, then ignore this!


Please consider following the Yost Serial Device Wiring Standard for RJ-45 connectors. I’m pretty sure this is the standard that Cisco and other manufacturers follow.

It’s probably important to note that the cables used in this standard are not straight-through Ethernet cables. It specifically calls for a roll-over cable, so each transmit pin connects to its corresponding receive pin at the other end of the cable.


@AlanS I agree with a caveat. I’d actually suggest that it be pinned out on the board side to support using a straight through Ethernet cable (so I guess have it reverse pinned out?).

Something one has a bunch of lying around the datacenter/house: Ethernet cables
Something one doesnt: roll-over cables.

Obviously this would have to be disclosed appropriately.

@Josh_Cook If you’re good with sending over the schematic, my buddy can crank out a pcb layout in a day or two.

@Mike_D All good, I’m mostly done just need some of those finishing touches. I am using the rs-232 standard pinned out to a DB-9 connector. My connector has DCD on pin 1, RXD on pin 2, TXD on pin 3, DTR on pin 4, GND on pin 5, DSR on pin 6, RTS on pin 7, CTS on pin 8, RI on pin 9. I use a FT231XS-R as USB to RS-232 and a HIN213EIAZ for the transceiver. So looks to be similar to RJ-45 in terms of the pin out.

Bugger. I have no clue what just happened, I closed kicad and reopened it (saved) and I was greeted with a surprise! Nothing left of the PCB, let’s do it again.

If anyone would like to help me out I have the schematic posted in my GitHub: Please be a good human and not steal my work.

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@Josh_Cook, my buddy got v0.1 cranked out and parts arriving Thursday of this week for assembly/soldering.

Note this is completely untested! (Caveat Emptor!)

I’m working on a 3D model for the enclosure now. Good news, is that since its USB-C (thank you framework), we should be able to test it on pretty much anything to see if it works.

Feedback welcome!

Forum wont let us post the SCH/BRD files, and we want to wait until its tested before we pusblish to github. DM me and I’ll happily send along what we have now.


Thanks. If you have seen any of my posts, I am in Australia but nonetheless I can get a PCB made for myself and assemble it, as long as it tests all good. Quick note, as the IC’s will have to be configured through the debug header, the led’s are in reverse, so if the device that you are connected to is transmitting it will has the RX light on. If you wish to change that you can just swap the colours around. For the FTDI setup it’s pretty self explanatory but CANBUS0 = PWREN#. CANBUS1 = RXLED# .CANBUS 2 = TXLED# .CANBUS3 =SLEEP. If you do wish to swap the leds so it is in the perspective of the laptop put the blue LED in the place of RX and the red LED in the place of TX.

I will more than likely modify my design for a USB-C to TTL serial and UART converters. As well as many different connectors like Micro USB 2.0 which I have the parts and PCB on order shortly after I figure out the issue with my design software not wanting to wire up the USB-C port. Any other ports you like to use in the field that hasn’t already been made?

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@Mike_D Hey, can I get the design files so I can get the PCB’s and parts on order?


@Mike_D Can you use a have port that would allow it to fit in the expansion card size the community will work on building the proper housing for it so it can still function as intended while still looking like it is meant to be part of the laptop.

@Josh_Cook Responded to your DM

@Skyline1029 I mean, we could, but you’d have to use a custom adapter cable to get to either DB-9 or 8P8C and at that point, just use a USB to Serial one =).

Framework has mentioned clearly that they’re going to support an RJ45 Ethernet port at some point. If they do one of the folding jaw ones, we might try to emulate that (if I can find parts), otherwise it’ll just have the 8P8C connector sticking proud of the chassis.

We’re doing fixed port rather than folding, since wouldn’t have ended up being a substantial size improvement with the design direction we’re going in.


@Mike_D This is great! I uhm… collect, enough switches and routers that this is a game-changer. Can’t wait to see the tested product!

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@courcelle12 We already have a prototype, failed to enumerate so will take the RS-232 - RJ-45 out of the equation and try the RS-232 on its own. And try it with type a not type c to see if there is any issues with using type C.

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