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USB 3.0 applicability to Astrophotography



In my ongoing frustration with USB connections, I was thinking about USB 3.0 hubs, and active repeater cables, under the assumption that the USB 2.0 device traffic would be aggregated and sent down the wire at USB 3.0 speeds.


It turns out not to be the case. In fact, USB 3.0 hubs and cables have completely separate data paths and wiring for USB 2.0 traffic, as described here:




USB 3.0 hubs and cables act identical to USB 2.0 hubs and cables, when all the devices plugged in are USB 2.0, so there is no advantage (unless/until one or more of your devices are USB 3.0).


If anyone has a different understanding please chime in.




PS I'm now experimenting with a 15m (vs. my previous 20m) USB 2.0 active cable to see if it is any more reliable. All my stuff lives outside (under a 24x365 scope cover and usb hubs inside tupperware) and I find I need to spray all the connections with contact cleaner each time, to get reliable connections, and often struggle with one or more devices not working. It's not a bandwidth issue. I can run two canon cameras, a focuser, a filter wheel, the mount (with ASCOM pulse guiding) and PHD2 with SSAG all at the same time without problems, when things are working ;0) 


The contact cleaner I'm using is http://www.amazon.com/gp/product/B00006LVEU/ref=oh_aui_search_detailpage?ie=UTF8&psc=1


The connections on the laptop side are also an issue, with one not working at all (hmm... need to re-try with the 15m cable). I attribute this to strain on the usb solder connections on the dell ultrabook motherboard (which I have had replaced once already).

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I would agree that the earths can be linked to improve performance, however are all the devices -ve earth. I.e. the -ve pole is connected to the equipment chassis?


If they are not, you could end up with a very expensive fire ;^))



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That would imply a power supply with three wire output. All of mine have two wires, so the negative HAS to be "earth", at least once you connect it to a device with USB cables. If that was not the case, the USB cables themselves would be the source of your fire.

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Another long usb cable issue:


Moisture in the repeater housing. 


First rain in northern Calif. in a LONG time, and I was out of town and my long usb cable was left outside (as usual). When I got back skies were clear but when I went to fire things up I got "A usb device has malfunctioned" and it turned out to be the extension cable itself.


Fortunately a hair dryer, applied liberally to both ends and the repeater in the middle of the cable  solved the problem (at least with testing in the house). I've ordered some "liquid electrical tape" to try to waterproof the repeater, and put the cable back into service outside. 

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Another "Long USB Cable" learning last night, also having to do with signal grounds.


I've been slowing learning to use a Mallincam astro video camera. I have it on a flip mirror so I can still use BYEOS & AstroTortilla for plate solving. The Mallincam is controlled via a USB to rs232 adapter.


Two nights in a row, I got everything set up on target sitting out by the scope, venturing inside when my laptop battery got low. Both nights the Mallincam became disconnected as soon as I sat down inside and plugged in the laptop power. No amount of reboots etc. seemed to restore things to normal working condition.


When it happened the 2nd time last night, I sat and thought about why would it fail in the house? What was different about being in the house? Plugging the laptop into AC power! I grabbed another power supply out of my backpack and checked the impedance between the ground on the AC plug and negative outisde connector on the laptop side; a direct connection. Then I recalled that the power supply I had been using, was not connected all the way to the wall with a grounded extension cord. The extension cord I was using was 2 wire. I plugged the 2nd supply directly into a grounded outlet, connected to the laptop, and presto, everything worked again.


So, moral of the story, make sure your laptop power supply is connected to a properly grounded outlet, when using a long USB cable!

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I learned something critical yesterday I wanted to share that affects the reliability and connectivity of astro gear.


If you have multiple power supplies, say one for your camera, one for the mount, and one for the USB hub, things can be greatly improved by creating a common ground. Tie the negative leads of all power supplies together.


I have three power supplies, one @12v for the camera 7.5v DC to DC converters, and the water pumps and fans for my camera cooling rig. Another at 12v for the usb hub, and a third @18v for the mount. Overtime I've had increasing reliability problems, where I was constantly fooling with the usb connections and cables to get things to work reliably. Recent symptoms included the mount constantly disconnecting from ASCOM applications, and the mount position, shown in my planetarium program, lagging behind the actual position during slews in jerks and stops. Also the camera wouldn't connect in BYEOS with out multiple fussings with the USB connections, plugging in and out cleaning, etc. 


After creating the common ground, all of that went away immediately.


I guess we'll see over time if this is a permanent fix but it makes sense that otherwise the USB cables themselves have to deal with any current flowing between the supplies and the data levels could fluctuate as a result.


This would also apply if you are using multiple batteries when remote. Say, one for you laptop and one for everything else. I suggest you connect the negative leads of both batteries together, to create a common ground.

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This similar to USB 1.1 and 2.0.  As soon as you plug a 1.1 device in your 2.0 hub with other 2.0 devices the communication speed between the computer and the hub drops to 1.1 speed.  Sad but true.  Looks like 3.0 to 2.0 behaves the same.



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Well not quite the same, as there are separate parallel data paths and wires for 3.0 and 2.0, so I think plugging in a 2.0 device won't affect your 3.0 bandwidth.


However, your comment makes me wonder which of my devices might be 1.0? Can you tell in the device manager or other windows software?


For instance if I have a usb 1.0 USB to serial adapter maybe I can/should swap it for a 2.0?

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