I interfaced a USB industrial digital camera to my PC using a 1.5 M USB 2.0 cable, and the camera was detected by the PC. But because of a length issue, I added a USB extension of 5 M length to interface with the PC.
Initially, everything was fine. But after two days the PC stopped detecting the camera through the USB extension. If I remove the USB extension and connect the camera and short cable directly to the PC as originally configured, it still works fine. The USB extension cable is fine, because when I use it to connect a pen drive, it is detected.
- Why was the camera detected initially and not now?
- I used a USB extension without an extra power supply. Could this be the reason? If so, then why was it detected and working for two days through same USB extension?
1 Answer
It sounds like all of the components are fine, it's the combination that's the problem.
- Passive extension cables aren't supported by the USB spec. In general, cables are designed for their length. Long cables will have larger wires than short cables, and other design differences. The losses and signal degradation in each cable are additive so even if the combined cable length is less than the suggested limit (5 meters for USB 2.0), the component cables may not support the combined length.
- It is possible to create a working cable longer than the 5 meter limit, and a longer non-custom cable might work with some devices. But it is unreliable for anything demanding. An off-the-shelf 5 meter cable added to an off-the-shelf 1.5 meter cable isn't likely to be reliable for anything demanding.
- The question in your case isn't really why did it work for 2 days and then stop, it's why did it work at all? We will never know the answer to that. Apparently, the combination was right at the edge of what would work at all, and it did manage to work for a short time (at least well enough for the camera to be detected).
- If you can move the computer to within 5 meters of where the camera needs to be, you should be able to use an off-the-shelf cable. Otherwise, you will need an active extension. You can use an active extension cable (referred to as a repeater), or an inexpensive powered USB hub to connect a standard additional cable. An active extension cable is basically a one-port USB hub built into the cable, as opposed to a passive extension cable that is just wires.
