ZWO ASI 120MC-S - long cables ?

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Hi all

I’m just hatching a plan to build a sky cam using one of these cameras (or similar). However, to get this camera in the location I would like I’ll need approximately 7-8m of USB cable running from the camera to my laptop in the shed/mini obs. So, I’m guessing a 10m cable will be the nearest I can get.

Is this realistic or will it be a hassle to get it working ?

Thanks

Gary

[Anthonyexmouth]

i use a 15m usb cable at the moment for my setup, shouldn't be an issue

[david_taurus83]

You can get USB repeater cables that boost the signal for longer lengths. About a tenner for 10m ones on Amazon.

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7 hours ago, david_taurus83 said:

You can get USB repeater cables that boost the signal for longer lengths. About a tenner for 10m ones on Amazon.

 

Thanks for this. I'm sure I read somewhere that some people had reliability issues when using repeater cables with astro gear outdoors, should I worry about that ?

I'm a complete duffer with stuff like this tbh, I'm not sure if a standard cable would still work up to 10m or if a repeater cable would definitely be required for that sort of distance ?

 

 

[cjdawson]

The longer the cable the better quality that you need.  USB was only designed to run over a couple of meters, which is why the longer cables are not common.  The longest cable that I've seen without a repeater is 5 meters.  And from what I remember of the specs of USB, anything longer and you need an active repeater.

 

I've successfully run 3 good quality cables over 5 meters.   Actually that's a bit of a lie as one time, one of the 5m cables (a USB 3 cable) refused to connect properly.  It was only on one occasion that it happened, but was still annoying when it occured.

 

Of course, your mileage may vary.

[noah4x4]

An ASI120MC has a resolution of  1280 x 960 so you should have no problem with 'active' USB cables over this distance. However, readers with larger sensor, higher resolution cameras should be cautious about USB which rapidly falls away with distance as regards data capacity.

Your next consideration might be how do you adjust focus or otherwise remotely control your scope, mount or whatever you propose? I mention this because having a narrow FOV might mean quite frequent adjustment and many projects also start with sequential single objectives when it is wiser to look at holistic challenges. If unplanned, you might then end up with multiple long cables when a wireless solution perhaps using two old laptops and RDP or TeamViewer might be appealing. But once again, the greater the demands of the camera, the greater the connectivity challenges. 

[JamesF]

12 minutes ago, noah4x4 said:

An ASI120MC has a resolution of  1280 x 960 so you should have no problem with 'active' USB cables over this distance. However, readers with larger sensor, higher resolution cameras should be cautious about USB which rapidly falls away with distance as regards data capacity.

I don't think the volume of data is the issue here to be honest.  The requirements of the USB specification effectively put limits on what can be achieved.

For example, it is a requirement that a signal pushed in at one end of the USB cable must appear at the other end within 26ns.  The speed of an electrical signal in copper is about 5ns per metre I think, so that effectively sets an upper limit on the cable length of 5m.  The speed does vary slightly however, depending on the construction of the cable, so it may be possible to push things a little further with high quality cables.  USB3 has further requirements that I believe limit the theoretical maximum cable length to 3m.

It's also entirely possible that some USB hardware implementations are more tolerant of out-of-specification signalling than others, so what works for one person using one chipset might not work for someone else whose machine has a different chipset.

USB3 interfaces can also run as USB2 (the sockets are even designed to allow connection using USB2 cables).  I don't know if this can happen or whether the USB spec. bans it, but it strikes me that it might be possible for a USB3 interface, finding itself in a situation where signalling is out of spec might actually drop back to USB2, thus appearing to work.

So I think the OPs best bet is to use decent quality cables including an active repeater and keep the cable runs as short as possible.  If anything else works then be happy with your good fortune, but be prepared for some unreliability.  Perhaps it might be worth experimenting with a few different arrangements of cabling, too (where possible, externally powered repeaters/hubs might be better than those powered from the USB cable itself, for instance).

James

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Thanks all for your advice.

For me the safe and familiar route would be a long cable linked to my laptop in the shed. However, I have also seen these DIY wireless raspberry pi cams online that look pretty cool. While this intrigues me, I have no knowledge of raspberry pi, how they work, what they might be capable of or their reliability. I also have zero experience of programming computers of any kind ! I’m guessing this option would solve the long USB cable issue but it might bring a whole load of other problems to a tech-duffer like me ?!