The weird part is that the camera works fine when I plug it directly into the Pi. The moment I put the 15-meter cable extension in between, it stops working. I followed the instructions here: Redirecting...
/dev/video0 does show up when everything is plugged in, but OpenCV errors out. I already went through and made sure all the connections were properly seated, and it made no difference. Honestly I never got this combination to work at all.
Thanks for all the detail, that helps a lot. Two things so I can narrow this down:
Can you paste or link the exact OpenCV error output you’re seeing?
Are you using picamera2 on that Pi, or something else to grab the frames?
The fact that /dev/video0 appears but capture fails usually points to something going wrong lower in the pipeline, so the error text will tell us a lot.
I don’t really have any standalone script to share, I’m just working off the instructions in the doc I linked above.
Something else that’s been bugging me: the Cable Extension product page says the kit works with all cameras, but the description further down says “The kit works out of the box with any of the following cameras:” and the OV7251 0.3MP is not in that list. So does the cable extension actually support all cameras, or only the ones listed there? If it’s supposed to support mine, what steps do I need to follow to get it working with the OV7251 0.3MP?
Ah OK. So does that mean the extension just isn’t compatible with this camera at all? I’ll check on the picamera2 thing and report back what I get from that command.
To be clear on my setup: the camera is fine on its own, the failure only happens with the 15m extension in the path, and /dev/video0 is still there when everything is connected.
Right — we tested it today on our end, and the result is that the cable extension doesn’t support this camera. So the OV7251 0.3MP + 15m extension combination won’t work, which is why you’re seeing it fail only when the extension is inline. The extension kit description listing supported cameras out of the box is the accurate part — the OV7251 0.3MP just isn’t one of them.
Separately, for the OpenCV errors: I still need to know whether picamera2 is installed, since that determines what the error output actually means. Please run the check above and let me know the result.
Tested on our side: the 15-meter Cable Extension Kit does not support the OV7251 0.31MP monochrome global shutter camera, so that combination won’t work on the Pi 4B.
The extension kit’s out-of-the-box compatibility list doesn’t include the OV7251 0.3MP.
The /dev/video0 device still enumerates when connected, but OpenCV capture fails (your error output: Yld.Me - gmxI).
Next step to close out the OpenCV side: confirm whether picamera2 is installed and share the output. Once we know that, we can tell whether the error is coming from a missing library or from the extension itself.