USB data over HDMI cable

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ashtonaut

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#296060 17-May-2022 16:09

I have a situation where the only physical link between a PC and a USB device (a webcam) is a permanently installed HDMI cable (about 5m long).

I need a USB connection between the devices, not a HDMI connection. I only need the USB data connection as power to the device is from a separate supply.

Is there any way to get the USB device and the computer connected using the USB protocol, but with a HDMI cable in the middle?

I know the immediate response will be "no".

However, I'm interested in any creative ideas, hence posting in the gadgets and electronics forum :)

For example, could I cut the plugs off the HDMI cable and solder USB plugs on the ends of the cable, using just 4 of the HDMI copper cores for the USB connector? Could I purchase some kind of active adapter? Is there some physical property of an HDMI cable that makes it incapable of carrying USB data?

Thoughts welcome.

richms

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#2915232 17-May-2022 16:28

I would get some HDMI break out adapters and just try running USB over one of the pairs in the cable, assuming you only need USB 2 speeds.

Richard rich.ms

wellygary

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#2915233 17-May-2022 16:33

You only need two wires for USB data.. the two outside pins (USB-A) are power....

Adapters do appear to exist, but a home-brew solution might be cheaper

https://themarket.com/nz/p/usb-3.0-to-hdmi-adapter/5557-6635714085073?skuid=10342280&utm_source=google&utm_medium=cpc&gclid=EAIaIQobChMIm_763Nnl9wIVDCUrCh0GqQdvEAQYBSABEgLBevD_BwE

ashtonaut

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#2915240 17-May-2022 17:06

Thanks. My concern is that the adapters for sale look like they are for converting video to USB for transmission. I want to send USB data down an HDMI cable.

HDMI breakout adapter might be something to look at.

Thanks

richms

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#2915243 17-May-2022 17:23

wellygary:

You only need two wires for USB data.. the two outside pins (USB-A) are power....

Adapters do appear to exist, but a home-brew solution might be cheaper

https://themarket.com/nz/p/usb-3.0-to-hdmi-adapter/5557-6635714085073?skuid=10342280&utm_source=google&utm_medium=cpc&gclid=EAIaIQobChMIm_763Nnl9wIVDCUrCh0GqQdvEAQYBSABEgLBevD_BwE

You need the ground too, otherwise they will not link up reliably. Its not a true 2 wire connection.

Those are a display adapter that outputs over USB, not useful for what the OP needs.

Richard rich.ms

Zorg2000

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#2915523 18-May-2022 12:13

You should be able to cut the ends off the HDMI cable and just use 4 wires to connect a couple of male usb connectors assuming similar gauge wire. https://www.aliexpress.com/item/32963245331.html?spm=a2g0o.store_pc_groupList.8148356.11.382924faKPxLoT&pdp_npi=2%40dis%21NZD%21NZ%24%200.31%21NZ%24%200.18%21%21%21%21%21%402100bdd516528326230048237e9320%21%21sh

Seems like a waste though. Can you not just pull a usb cable through using the HDMI cable?

Speedy885

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#2915827 19-May-2022 01:33

Zorg2000:
You should be able to cut the ends off the HDMI cable and just use 4 wires to connect a couple of male usb connectors assuming similar gauge wire. https://www.aliexpress.com/item/32963245331.html?spm=a2g0o.store_pc_groupList.8148356.11.382924faKPxLoT&pdp_npi=2%40dis%21NZD%21NZ%24%200.31%21NZ%24%200.18%21%21%21%21%21%402100bdd516528326230048237e9320%21%21sh

Seems like a waste though. Can you not just pull a usb cable through using the HDMI cable?

I second this however the nerd in me would buy some female HDMI Connectors and solder them up to USB Sockets if the HDMI can not be used as a draw wire. One thing to note though is USB is certainly limited when it comes to Cable length without an active Circuit. 5M and up usually have the extra Circuitry however you may get away with up to 7M if you double or triple up the cores in the HDMI Cable to avoid Voltage Drop etc.

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ashtonaut

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#2915830 19-May-2022 05:42

Thanks for the suggestions. I think I’ll pursue HDMI breakout plugs connected to USB plugs, potentially doubling up cores.

The hdmi cable is permanently concreted into the floor (don’t ask) hence the desire to find a ‘non-standard’ solution…

Looks like I can have a go with parts from Aliexpress for about $20, which is only a minor investment.

catdog

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#2915904 19-May-2022 10:46

potentially doubling up cores

Don't do this!

The data pair are a controlled differential impedance, typically 90 or 100 Ohm. If you double up the cores you will mess up this controlled impedance, causing reflections, and it wont work.

You could double up on the GND/5V cores, but since you already said that the device gets power from a separate supply this is probably unnecessary (Voltage drop = resistance * current. Since power is from a separate supply, then current is close to zero, so voltage drop is close to zero). You should still connect a single core for each GND and 5V as some devices will use this power to detect when it's connected to the PC.

Overall I suspect that you might have difficulty getting a reliable solution here. As already mentioned, USB2 spec has a max cable length of 5m, so you'll need to keep any extra cables at each end as short as possible. You'll need to be careful building your adapters to try to minimize reflections where the differential impedance through your adapter doesn't match the cable impedance (ideally using a PCB with the differential trace impedance between the connectors matching the spec, otherwise keeping the wires as short twisted pairs between the connectors). And obviously make sure that you are connecting each USB data pair to an HDMI data pair in the cable.