Multiple USB scanners on same host PC?

[dgsmith]

With the scanners in our school, the setup we have is that each scanner has a host PC which when the button is pressed on the scanner, the scan will save in a shared area (thanks to dhicks for suggesting this some time back)!

Whilst this is all good, it does mean we have to have an unattended PC by each scanner, not only wasting power but also prone to being "knocked" or turned off/unplugged and then people wonder why it doesn't work!

I have thought about buying some USB extenders over cat5, which in theory would allow me to connect these USB scanners to this extenders, and for them all to terminate in at our cab, where just a single host PC would handle all the scan requests.

Is this doable? Before money is spent on these extenders, I want to know whether it is possible to have multiple scanners attached via USB to a single PC and for each to operate independantly (each scanner has different config and saves its scans to a different folder and can also scan if another scan is happening). It would save us some money in power and mean the computer won't be the cause of the problems we sometimes see now.

For ref, the scanners are all Canon Lide 20 (quite an old model).

[smadison]

We have networked photocopiers set-up to scan to a network share and it works better than having scanners all over the place. If your photocopiers can be set-up for network scaning it may be worth a go.

[dgsmith]

Our photocopiers are in 1 place and students aren't allowed to use them. Our scanners are in each ICT room and students are encouraged to use them. The setup we have now is simple, however I always thought there was room for improvement without changing the setup entirely.

I've read a little into SANE (alternative to TWAIN driver), however i've no idea how that works or how relavant it is..

[dhicks]

Before money is spent on these extenders, I want to know whether it is possible to have multiple scanners attached via USB to a single PC and for each to operate independantly (each scanner has different config and saves its scans to a different folder and can also scan if another scan is happening).

Hmm. You could potentially check by plugging two scanners in to one PC and giving it a go. However, I'm guessing that the scanners draw near the top level of power available from the USB port (they do have to power a bulb and scanning hardware, after all), and plugging two in to one USB hub might give power issues. The Cat5 extenders, no doubt, provide power to each individual USB device anyway, so power shouldn't be a problem for the actual solution you have in mind. You might want to plug each scanner in to one PC via separate, powered USB hubs.

--
David Hicks

[Arthur]

Those Canon LiDE 20 scanners are USB 2.0 Full Speed devices a.k.a. USB 1.1, so scanning is going to be extremely slow particularly if they are all being used at the same time.

Before you do this, I would check Device Manager and find out how many USB "root hubs" you have on the computer you intend to use for this task (the more the better). While each root hub is capable of supplying the full bandwidth to a device regardless of what the other root hubs are up to (in your case 12Mbps* because the scanners are USB 1.1), almost all motherboards still only have two EHCI controllers and each controller has to share its bandwidth amongst all devices attached to it.

Another thing to consider is the fact that almost all USB hubs only have a single transaction translator (TT) - because they are much cheaper to manufacturer - which means the bandwidth is again shared amongst all the ports on the hub. You can get Multi-TT hubs (like this one) but they are quite rare.

As David mentioned above you will definitely need to power the USB hubs themselves. Without this they will only be able to draw a maximum of 100mA from the USB port it is connected to. I don't think a scanner would be able to work with this amount of power.

I've not checked myself, but you may also find that the scanner driver/software saves the settings for the button on the front to a single key in the registry. If this is the case, then I don't see how you could configure multiple scanners to save to different locations because they would all be reading the same registry value. I may be wrong on this though.

By the way, this article is quite interesting since it explains much of the above better than I can.

* Due to the overhead of the USB protocol you will never get the full 12Mbs. You will also notice that Windows reserves some of the total bandwidth too (upto 20%).

[dhicks]

I've not checked myself, but you may also find that the scanner driver/software saves the settings for the button on the front to a single key in the registry. If this is the case, then I don't see how you could configure multiple scanners to save to different locations because they would all be reading the same registry value.

I suppose you could run multiple Windows XP VMs on one machine, assign them each a separate USB port with a scanner attached?

--
David Hicks

[dgsmith]

However, I'm guessing that the scanners draw near the top level of power available from the USB port (they do have to power a bulb and scanning hardware, after all), and plugging two in to one USB hub might give power issues.

Those Canon LiDE 20 scanners are USB 2.0 Full Speed devices a.k.a. USB 1.1, so scanning is going to be extremely slow particularly if they are all being used at the same time.

Before you do this, I would check Device Manager and find out how many USB "root hubs" you have on the computer you intend to use for this task (the more the better). While each root hub is capable of supplying the full bandwidth to a device regardless of what the other root hubs are up to (in your case 12Mbps* because the scanners are USB 1.1), almost all motherboards still only have two EHCI controllers and each controller has to share its bandwidth amongst all devices attached to it.

Another thing to consider is the fact that almost all USB hubs only have a single transaction translator (TT) - because they are much cheaper to manufacturer - which means the bandwidth is again shared amongst all the ports on the hub. You can get Multi-TT hubs (like this one) but they are quite rare.

As David mentioned above you will definitely need to power the USB hubs themselves. Without this they will only be able to draw a maximum of 100mA from the USB port it is connected to. I don't think a scanner would be able to work with this amount of power.

Thanks for the input chaps. I'm not sure in which context you mean "hub"? If this method worked, the plan would be to plug each scanner into its own USB port on the motherboard, rather than using 1 port and splitting with a hub. I can see in the device manager that each port is assigned 500mA and that is exactly the amount these scanners use, so I am hoping that power shouldn't be of concern.

The usb extenders over cat5 I have my eye on unfortunately don't have an external power supply (the expensive ones do), however as cat5 can transmit power easily, and these devices are designed to imitate a single USB cable, I hope this shouldn't be an issue.

I've not checked myself, but you may also find that the scanner driver/software saves the settings for the button on the front to a single key in the registry. If this is the case, then I don't see how you could configure multiple scanners to save to different locations because they would all be reading the same registry value. I may be wrong on this though.

That is a good point and besides the fact that the standard windows TWAIN driver may not be capable to operate two scanning devices at the same time, I hadn't thought of registry config. I suppose any probllems in attempting this approach would be down to software limitations as opposed to hardware limitations. I've even considered virtual computers within the host PC but that is starting to seem overkill for a solution that does already work now. Then again, I suppose once it is setup, it can just be left..

As I said before, I see there is a SANE project to allow many scanners to be shared/used over the network, however I barely know anything about it and alot of it involves the *nix platform to which my knowledge is scarce.

[p858snake]

What about using thin terminals/dumb clients for managing them?

[jamesreedersmith]

Just watch as the longer the cable the greater the voltage drop and therfore a long run may not power the scanner suuficently to work.

Thanks
James

[dgsmith]

What about using thin terminals/dumb clients for managing them?

How would this differ from using standalone XP stations we have now? My two aims are to remove the machines into an attended environment (our office) and reduce the amount of them so as to cut down on wasted power.

Just watch as the longer the cable the greater the voltage drop and therfore a long run may not power the scanner suuficently to work.

I thought about this, however as the runs aren't too long (we're next door to the ICT areas practically) this shouldn't be too much of a problem. We also run IP cameras over PoE which have distances around 50m - these scanners will be nowhere near that distance from the cab though!

[jamesreedersmith]

I thought about this, however as the runs aren't too long (we're next door to the ICT areas practically) this shouldn't be too much of a problem. We also run IP cameras over PoE which have distances around 50m - these scanners will be nowhere near that distance from the cab though!

The problem comes that usb is only 5v and most POE is 12-48v therfore a small voltage drop is a greater percentage of a starting usb voltage as opposed to full POE - only way to be sure is to try it though!

[dgsmith]

I'm hoping it won't be a problem - i'd understand if the distance was long but the distance really won't be too long at all (12m max).

The extenders I am looking to use are these from BT Business which are cheap but hopefully would do the job.

I'm thinking maybe using virtual machines may be the best way of achieving this, especially if the scanner config in the registry is only setup for 1 scanner!

[Arthur]

I'm not sure in which context you mean "hub"? If this method worked, the plan would be to plug each scanner into its own USB port on the motherboard, rather than using 1 port and splitting with a hub.

For some reason, I imagined you were going to have eight (or more) scanners connected to multiple USB hubs.

That is a good point and besides the fact that the standard windows TWAIN driver may not be capable to operate two scanning devices at the same time, I hadn't thought of registry config.

If you do have this problem you should be able to get around it using the registry redirection feature of Microsoft's Application Compatibility Toolkit.

[srochford]

I really like the VM idea - I can't see why it wouldn't work (but that doesn't mean it will!) I'd definitely try it - it would be quick to set up a machine with a couple of VMs and connect a couple of scanners. Once you know the technique works you can then look at using USB extenders. Again, for the distance you're thinking of, I think it ought to work.

[Arthur]

The VM idea does sound good. However, what would happen if a student disconnected a scanner? When it was plugged back in would it get automatically reconnected to the correct VM?