Modern, high-speed astronomy cameras like those from Altair, QHY and ZWO are wonderful, but they do tend to push the USB system of your computer or laptop right to the limit. Sometimes they push it a bit beyond the limit and everything goes wrong, leading to strange bugs, crashes or application freezes. This post gives some guidelines and tips for avoiding USB problems or curing them if they do happen.
Step 0 - Check the settings
Some cameras have USB speed parameters, which you might need to adjust to let them use more (or less) of the available USB bandwidth in order to get satisfactory operation.
Step 1 - Back to basics
If you are having unexplained issues with a camera or other hardware the first step is to go back to the simplest setup possible. Remove any hubs, extension cables and other hardware and just connect the camera to the PC using the manufacturer provided cable. If the camera works fine like this then other problems you are seeing are very likely caused by USB cabling issues (see later section on USB Cabling tips). If you are still having problems, move to step 2
Step 2 - Update
Make sure you have installed the latest version of the manufacturer's drivers for your device and the latest version of SharpCap or other imaging applications. This is particularly important for recently released cameras which may not be supported in older versions
Step 3 - Check the cable
It's very rare, but now and then you get a faulty cable with a camera, or perhaps the cable might have been damaged in some way. Swap the cable for another one of the same design and similar length just in case. If you have a USB3 camera, check that you have a USB3 cable (they tend to have blue plastic inside the plugs).
Step 4 - Try a different port
To get best results, your camera and your computer's USB system have to work together at very high speed. Some cameras just don't get on with particular USB ports for reasons that are not clear. If your PC or laptop has more USB ports, try switching between them and see if you get better results in a different port. It may sound weird, but it's worked for a number of people because different ports on the same PC may have different types of USB controllers running them - the one's on the right might not work so well but the ones on the left might be fine.
Step 5 - Check USB controller drivers are up to date
If you have a USB3 camera and the camera is detected but you never get an image, out of date USB controller drivers could be an issue. Go into 'Device Manager' and look for 'USB 3.0 eXtensible Host Controller' entries. If you see a version of 0.97, try to find an update for that device to 1.0 which I've seen fix this problem.
Step 6 - Try a different PC
By testing on another computer you hope to work out if the camera itself is working correctly - if it works fine on another computer then the chances of it being faulty are very slim.
USB Cabling Tips
If your device works correctly when you go 'back to basics' with a single USB cable, but fails with more complex cabling, then read through the tips in this section.
1. Absolute Maximum Cable Length
The maximum allowable cable length between USB devices is 5m. This means the cable length from PC to device or from PC to hub or from hub to device. You can build longer lengths by using hubs (or active repeater cables, which are basically a cable with a built in hub). So, you could have
PC -> 4m -> Hub -> 4m -> Camera
to get a total of 8m and it would have a reasonable chance of working, but
PC -> 8m -> Camera
will not work at all
2. High Quality Cables will *NOT* allow you to exceed the 5m maximum length
The limitation isn't to do with signal loss along the cable, it's to do with signal timing and the speed the signals move down the cable. Cheap and nasty cables however may reduce the maximum length that works!
3. Practical Maximum Cable Length is *NOT* 5m
Experience has shown that while a 5m cable run will work pretty well for something with a low data rate - like a keyboard, mouse, mount or focuser, it doesn't always work reliably with a high speed USB camera. I have found that cables over 4m start to have problems for USB2 cameras and over 3.5m can give issues for USB3 cameras.
4. If possible, give everything it's own port
By far the most reliable way to get multiple USB devices working is to take each and every device back to the PC separately with no hubs involved. If your PC or laptop doesn't have ports for this then the second best option is to use a hub for low data rate devices (mount, focuser, filter wheel, etc) and to bring the cameras(s) back to the PC on separate ports.
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