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A USB 'junction box' - Is there such a thing?


swag72
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Sorry for the complete lack of technical jargon or knowledge!!

I want if there is such a thing as a USB 'junction box' type of thing. I want to put all my USB cables from the scope etc into a 'box' that I can mount in a safe place and then have another set of cables running from this to the PC. As it stands at the minute I have to move the lappy around to take account of cables. With this, I could avoid that issue.

Hope that makes sense - Perhaps there isn't such a thing?

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Yes they are call USB hubs .. come in various types .. unpowered or powered... I personally always prefer powered ones but it really depends on what kit your pluging into it at the mount end...

On neat option for low power devices or ones that use their own batteries or external PSU's is a Cable Hub... this is a single cable PC end which splits into a number of USB ports at the remote end..

http://www.maplin.co.uk/usb-2.0-4-port-cable-hub-with-120cm-cable-104980

I would definitely but a USB2.0 standard one over USB1.0 standard..

You might also want to consider an active repeater/extender cable this will allow you to remote the computer...

http://www.maplin.co.uk/usb-2.0-12m-active-repeater-cable-444544

I know your in Spain but the maplin links are just to give you an idea what to look for...

Peter...

Edited by Psychobilly
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I was planning on remoting the computer via live remote from the warmth of my lounge!!

I am thinking of putting a USB hub (thanks for the correct word Peter!!) onto my pier so that I am avoiding the cabling issues that I have had from time to time, where they aren't long enough etc.

Would you recommend a powered or unpowered one? I would be plugging into it my QHY5 for guiding, My 1000D and the handset.

Also, what cables leave it? All USB - USB?

See, pier and obsy plans all in the middle of a big melting pot at the moment. Just need to feel comfy with brick built obsy!!

Edited by swag72
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In a hub, you have say, one usb cable that enters, and 4 usb cables that leave. If it is a powered hub, you will also have a power cable in, the other end is a elec plug with a transformer built in.

If you get one from the uk, you will need a uk adaptor for the transformer.

I would have a look wherever PC's are sold near you, say a dept store, or supermarket with TV and computer section, you should be able to pick one up quite cheaply.

Edited by wiseman
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In a hub, you have say, one usb cable that enters, and 4 usb cables that leave. If it is a powered hub, you will also have a power cable in, the other end is a elec plug with a transformer built in.

I will have 3 USB cables going in (camera, handset and guide cam) - That will all come out happily out the other end, right? Information isn't going to get scrambled, mixed up or lost? (Sorry I really am a dumb twit!!!)

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I've just looked at the Maplins link Peter - That makes 1 USB into 4 - So would I need 3 of these, one for each USB cable from the PC? Or are you telling me that the 3 USB cables that I have from the scope area go into this box and then only 1 cable needs to come out and be connected to my PC? WOW - If that's the case, that's a magic box! How does it know what to send to what? Do people use these for their astro stuff? You're saying that my QHY5, camera and handset would ALL get recognised through one USB cable?

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I do exactly the same thing Sara... You need 1 x 4 port hub. The single port connects to the PC, the other ports connect to the devices. I am using an unpowered hub, and driving the mount (self powered), the 450d (self powered) and the QHY5v (unpowered) and do not have power problems.

You can actually daisy chain hubs and run up to 128 different devices off a single USB port, in theory... I don't know anyone that has tried that though.

As long as the devices always plug into the same port on the hub, and the hub into the same port on the PC, no problems, if you change ports, the drivers will get installed again. I labelled my cables and ports on the hub to make it easier to put them back in the same place.

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I got a powered USB hub from Amazon UK plus USB active repeater extender leads to run from the house up into the sheds. The normal limit is 5m but you can put 5 of these special extender cables together plus and ordinary USB extension cable to go up to 30m. Amazon also sell the plain USB extension cables. I believe you have Amazon in Spain.

USB hubs :-

https://www.amazon.co.uk/LUPO-Octopus-Port-High-Speed/dp/B004EYIBH2/ref=sr_1_34?ie=UTF8&qid=1303806390&sr=8-34

https://www.amazon.co.uk/LUPO-Port-USB-2-0-Powered/dp/B003BVDABG/ref=sr_1_25?ie=UTF8&qid=1303805860&sr=8-25

USB active repeater extender :-

https://www.amazon.co.uk/USB-Active-Repeater-Extension-Cable/dp/B001IPWJ32/ref=sr_1_18?s=computers&ie=UTF8&qid=1303806646&sr=1-18

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There are two things with USB you want to plan on:

a) power

:) bandwidth

If you think of a USB 'bus' as a sewer pipe, a big pipe connects to your PC then each pipe that connects devices further down the pipe then shares the big pipe capacity. This can cause problems if one of the devices uses all the capacity.

How much of a problem is down to how good the hub is but putting a 22MB picture down USB2.0 when attempting to get a smooth stream of guiding photos is another matter.

I'd use one USB bus for the imaging transfer (ie plugged into your main imaging camera) then another bus for the smaller guide camera and mount control. The last thing you want is the accumulation of delays and to cause delays on guiding.

Inside the computer the speed (capacity) of the internal computer CPU/PCI-E busses (think massive pipes!) are so large that supporting full capacity of multiple USB connections isn't a problem.

Edited by NickK
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Sara, I would never called yourself a 'Dumb Twit', there is never such a question as a dumb question. If you do not know the answer, how can it be dumb? We all started in astronomy not knowing much and went from there, by asking questions you learn more and SGL is a very good place to learn about astronomy. I asked a question about CCD filters today, so we are in the same boat there.

If in boubt, hopefully somebody will be able to answer your questions.

Peter

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Just plug all your cables into the hub and then plug the hub into the single computer USB and everything will work.

USB devices have their own 'name' configured by the manufacturer so when the computer talks to to it*, it doesn't matter where it's connected - direct or through one hub or a daisy chain of hubs.

* usually.. but lets keep things simple.

Edited by NickK
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There are two things with USB you want to plan on:

a) power

:) bandwidth

If you think of a USB 'bus' as a sewer pipe, a big pipe connects to your PC then each pipe that connects devices further down the pipe then shares the big pipe capacity. This can cause problems if one of the devices uses all the capacity.

How much of a problem is down to how good the hub is but putting a 22MB picture down USB2.0 when attempting to get a smooth stream of guiding photos is another matter.

I'd use one USB bus for the imaging transfer (ie plugged into your main imaging camera) then another bus for the smaller guide camera and mount control. The last thing you want is the accumulation of delays and to cause delays on guiding.

Inside the computer the speed (capacity) of the internal computer CPU/PCI-E busses (think massive pipes!) are so large that supporting full capacity of multiple USB connections isn't a problem.

Mmm, interesting - Totally get it about the 'pipes'!! So, maybe I'll try 2 hubs then, one for the camera dn the other for the guiding and handset.

Thanks folks - You make it all so simple!! So, next thing is powered or unpowered? I suppose that the powered ones will better? More efficient?

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Think of it as the computer equivalent of an extension power lead with 4 thirteen amp sockets on it, you plug one end in to the mains, and then you can plug 4 plugs into the adapter.

Same with the usb hub.

When you buy it it has one usb lead on it. you plug that into the usb socket on your pc.

You then have 4 usb sockets available. one for QHY5 for guiding, , one 1000D and one handset. You have one spare!

I am assuming that you can put the pc close to all the three things you want to attach

This means that you just take the laptop to the hub, and plug one lead from the hub to the laptop.

I would guess this is simpler than using the longer run of repeaters, but as mentioned, the technology is available to do this. At my house this would fall foul of kids, dogs or chickens!

I would get a powered hub, that will save you changing it if you have problems later with power.

Just plug everything in, and the pc will recognise it.

Trust this helps

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Regarding the 'sewer pipe' analogy, it depends what software you are using.

For example, using Maxim DL, I have 3x USB 2.0 feeds

- EQMOD + guiding control

- autoguider cam

- the CCD main imaging camera

Here's the important part: When the main imaging camera downloads a frame to the computer, the telescope controls and guiding cam feeds go off, until the complete frame is downloaded. Once the image is downloaded, the guiding (cam + scope driver) restarts through the other 2 USB ports. Therefore the bandwidth does not get compromised by using a hub at the end of 1 physical USB line.

The other important thing to consider is if your main imaging cam's USB interface is buffered or unbuffered. If it is buffered then you're sorted. Even if the USB bandwidth were compromised by hubs or other interference, the image data (in theory) wouldn't be affected.

If you use separate apps for guiding, telescope control, and image capture from the main camera, then using a USB hub would probably be a bad idea, because the separate applications would have no knowledge of what each other is doing, so guiding commands and guiding image frames would continue to be transmitted at the same time as the main image download. In that case you want dedicated bandwidth between the main imaging ccd and the computer.

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Here's a few pics of the imaging rig I set up at the weekend Sara. Both the cameras, dew controllers, and mount controls, go into one 4-port USB2 powered hub. A single "active USB cable" goes from there to the house. I run off a field battery cos it's portable, but you might need to wire in an additional "mains to 12dc power converter" if yours is a fixed pier setup.

Stargazers Lounge - brantuk's Album: Telescopes

Cheers :)

Edited by brantuk
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I've yet to plan how I'm going to arrange my USB wiring and whether I have the control computer by the scope or a few metres away in the house. I'm going to have to run a pipe (conduit) under the lawn from obs to house. There's a lot to be said for running things from a nice warm cosy house :) Plenty of time for planning - computer controlled tracking is a fair way down the line. I can't afford to buy equipment as fast as I'd like.

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Personally unless the guiding and image capture is being done on a low power machine, it makes no real sense (and risk of loss) for the guide camera to stop tracking the extended target over the entire time. Usually the guide camera is only downloading a small sub-portion of the image to increase frame rate. If you loose too much time then you'll have to expand the picture just in case the star isn't where the predicted sub-portion is.

Theoretical maximum single USB bus transfer rate is 60MByte/sec, in reality that's 30-40MByte/sec. The EQ6 only talks at 9600 baud.. that's ~1.2KBytes/sec max (ignoring the real conversion to bytes/sec). I'm writing a controller for it at the moment (including controlling the USB-Serial chip). The guide cam, if it's like the 16ic, only transfers a sub-portion of the image other wise it's ~650Kbytes for the full image. The sub image may only be 128x128 pixels max and with the 16ic's FTDI bit bang mode - that 32Kbytes is transferred at a theoretical rate if about 2Mbit (~250Kbyte/sec) max.

The important bit here is latency rather than raw transfer rate - ensuring that the guiding signals are not delayed by collisions/congestion. This helps the guiding feedback loop control the position in the mount more accurately.

You could say this approach is to get the maximum out of the setup.. a single USB cable setup would work fine for the majority case :)

Sorry getting too deep- comes from being up to my eyes in writing software to interface things without using drivers and directly communicating to things over the USB bus.

Edited by NickK
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