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I found in the garbage an old USB webcam with an OV 518 chip. The USB cable that was going out of it, however, wasn't there. There were just some remains of the tiny red/white/green/black wires that are usually inside the USB cable. I do not know why, but there are two copies of the black wire.

Therefore I made a very quick contact (without tin, just by doing some knots) with a USB cable that I had cut in half. You can see it in the following picture: USB connection.

The camera is recognized by my computer (I use Mac OS X and macam ), but it complains that it has "not enough bandwith" and cannot do any acquisition.

Now, my question.

I do not know anything about the camera and it might well be that it is faulty for its own reasons, in which case I would return it to the garbage. But could it be that the bandwidth is low because of the horrible, handmade, connection? I do not know the USB standard so I do not know if the bandwidth depends on the quality of the connection. Is there a way, such as a software utility, to check the quality of a USB connection? If this is the case, I guess I could try to do a better connection and make it work.

EDIT: Now I have soldered the wires, so I made a stronger connection. The problem persists exactly as before

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Do you have any other USB devices plugged in? This is a guess, but you mentioned it's an old webcam. Is it possible that you are forcing USB 1.1 and that's the source of your bandwidth issues? Maybe USB 1.1 can't handle your webcam and the other devices on the interface. –  Nate Nov 13 '12 at 2:46
    
@Nate No, I do not have other devices plugged in. –  Fiat Lux Nov 13 '12 at 7:04
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The connection could well cause errors which manifest as low bandwidth. At the very least you should solder or crimp them. On the other hand the damage which removed the cable may have damaged something else. –  pjc50 Nov 13 '12 at 9:36
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/agree with pjc50. I don't know the USB standard so I won't post as an answer, but USB 2.0 (the camera is hardly 3.0) has three speeds: 480 Mbit/s, 12 Mbit/s and 1.5 Mbit/s. If the expected speed fails, it may well try a lower one, that might be insufficient. –  exscape Nov 13 '12 at 18:58
    
Is it just me, or is it very impressive for a webcam/usb driver or software to recognize that it has insufficient bandwidth and report it as such. –  Chintalagiri Shashank Jan 31 '13 at 21:00
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2 Answers

up vote 0 down vote accepted

The bandwidth message has to do with high-layer communications protocols. If you get that message, it means the physical layer works, but something is wrong at the protocol layer. Perhaps there's a bug in the camera, and that's why you could "find" it?

There is also a very small chance that the D+ and D- wires are reversed, which would cause the camera to be detected as low-speed when it should be full-speed. If the other option is to throw away the camera, you could try switching D+ and D- and see if it works any better, although I would give it a pretty low chance.

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Thank you for your answer! Unfortunately I have already disposed of that webcam so I cannot invert D+ and D- now. I accept your answer because it tells something about USB connections in general. –  Fiat Lux Jul 1 '13 at 15:54
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What do you mean 'two copies of the black wire'?

USB uses a voltage differential (3-wire) data bus cable with grounded shield to minimize interference from external sources. Your unexposed wires and unsoldered connections could be a source of noise.

With regard to thee bandwidth error, the macam FAQ mentions lowering image format frame rate. Did you try this?

There is also a bandwidth slider in the video settings dialog which can be adjusted to restrict the USB bandwidth.

You may also find this article of interest, in that it describe a problem with the way Mac OSX hands out USB bandwidth to isochronous devices.

For monitoring performance of your USB ports, the iStats Menu tool offers a range of status statistics including bandwidth performance.

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This is probably a reference to the shield vs the supply ground. –  Chris Stratton Nov 27 '12 at 20:13
    
Thank you for your answer, however I must clarify that I used all the possible options of macam to reduce the bandwith. Moreover, I tried iStat Menus and I did not find any way to monitor the bandwidth of the USB connections –  Fiat Lux Dec 2 '12 at 19:07
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