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Just a quick update. As you may recall, I found that using a USB on my Dell E4310 meant the speed of the other USB socket was impacted. In fact, when a GPS dongle was being used to set system time, it meant the error could jump from 2-3 ms to 20ms.
To try to overcome this, it was suggested I try an Expresscard based USB port. I bought a Startech dual USB2 port card, but had to return it as it wasnt recognised on Win7 – even after 30 minutes with one of their helpful online advisors. So I tried instead a CSL dual USB3 socket Expresscard for £10. After loading the drivers that was immediately recognised. It works fine with all the USB kit I tried. So I connected the GPS dongle up to that, hung a Paramount MEII tracking a satellite (22Hz tracking speed updates) on one of the laptop USBs and a Starlight 694 taking very short exposures on the other. Result can be seen above. For long periods the error was 2-3ms with occasional wandering to 4ms. Really not bad at all – plugging into the main bus made a big difference. Well worth the small installation effort.
So, if timing is crucial to you, get a standalone network enabled time source and set up your own NTP server. But if 2-3ms accuracy is good enough, £20 for a GPS dongle and a CSL card will do the business.
Thats interesting. As my previous problem had been using a USB sound sampler on a shared port, I thought I should check again.
So, I was out last night using a USB GPS dongle and NMEATIME2 to set my system clock to <0.005s accuracy, controlling a telescope from TheSkyX (which uses a USB to Serial converter to talk to a Paramount) and a Starlight camera via a USB socket.
The laptop I used was a Dell E4310 (Intel i5 at 2.4GHz with 4GB memory) which only has 2 USB sockets.
I noticed that when anything was sharing a socket with the dongle, the NMEATIME2 correction timings became erratic – it assumes GPS fixes from the receiver are evenly spaced I think. So, when I connected the telescope or when sharing with the CCD my timing precision was potentially off as the attached image demonstrates (the sharp change in the trace is when I connected the telescope). Not surprising I suppose, but the timesharing aspect clearly does have some an effect on other bus users. I imagine the impact will depend upon the nature of whats sharing the port and what laptop manufacturer/model you choose.
I will try again tonight if (wonder of wonders) we get two clear nights in a row using a Dell D630 which has 4 USB ports and post the results here. Alas, I only have Dell laptops and so cannot say how this pans out with other machines.
Do let us know what you find out. A commercial manufacturer of roll off roof sheds would be worth knowing.
Yes. That makes sense. Had wondered about getting an additional USB socket on an Express card. Hadnt thought of the docking station though (I do have one somewhere). Might get a spare docking station while they are still available – I have a feeling the later Dell models also have a connector, but its a different format – will worry about that when I upgrade (I’m a fan of kit thats oldish, so that when it breaks it is not an expensive event – good for the stress levels.).
Will grab a card and let you know how it turns out.
Glad to hear I havent got it completely wrong then. It is very reassuring to hear other people already do this.
I made sure the Dell I am thinking of is W7 rather than XP on because XP doesnt get security upgrades anymore.
Now, if I can just get the garden sorted and the redecoration done and the skirting boards replaced and the paths laid and the…..
This will be fun.
I did try a Dell D630 30ft away from the house in the garden, with a CCD attached and it seemed to work fine when accessed by Remote Desktop and a Wifi connection. It happily sat there taking 5s exposures for me and displaying them. I didnt even need to move my Hub from the other end of the house – I will probably add a repeater when I use it in anger (theres minor issue of putting a pier in, adding the mount/scope and adding an observatory to be overcome yet) or add a couple of ethernet cables to the trunking carrying the mains out there.
I’m not sure why more people are not using Remote Desktop. What dumb error am I making? Security? 🙂
A key fob on the roll off roof is pretty cool 🙂
Will indeed look out for well protected cables. We have foxes round here certainly – the footprints in the recent snow were really obvious. Other things too – though pheasants, deer and voles are not normally a problem for telescopes, but rather unwelcome in the nearby veg patch.
I noticed several people mentioned the software they use to access the instruments in the observatory from indoors. Sounds like there are several good options out there – and some of them free to private non-commercial users. Its nice to have multiple good choices. I’m rather favouring using Dell D630 laptop outside as they have 4x real USB sockets and are rather cheaper than decent spec NUCs – t he NUC may come later (its compactness is attractive). Dell D630s are certainly not the fastest machines in the world but good enough to run an autoguider and CCD at the same time.
Thanks for the comprehensive reply.
Fortunately, I am not going for a fully automated solution. In the absence of a shed that lends itself to automation I don’t think its worth the hassle for me just to avoid going outside in the dark/cold for 10 minutes at the start and the end of each session. Can see the joy and challenge in it though.
In light of what seems to be the opinion of USB over internet, I will probably go for a NUC hung on the back of the scope so all I need a is 5A 19V power supply cable and an ethernet cable connecting to them to Remote Assist/desktop via.
A thermostat/heater on the NUCs will be needed of course as few computer drives are good for operation sub-zero.
Still means trench digging of course, but theres no way round that without recourse to batteries and a big solar panel on the shed roof.
Shame no one in the UK manufactures motorised run off roof sheds that can be run from a PC. Theres a market niche.
Perhaps if my DIY To Do List was <1 sheet of A4 (8 point font). 🙂
Thanks again. Have you published any accounts of your observatory?
So the Pi handles the USB control locally (and presumably provides buffering) and then squirts it across the network as loading permits? Thats sounds fun and worth trying out. Four Pis are hardly expensive – I recall that in the earlier models Pis were internally a single USB port so I would probably need at least 3 if I use two imagers.
Thanks.
Thanks for that. The only colleague I could find who had used one much in anger was merely feeding keyboard and mice down one Cat5. Unsurprisingly, he didnt have much problem.
Thats an interesting presentation. Am I reading that right? The 1pps pulse goes straight into what appears to be an Arduino GPIO – should work!
Yes, the slow speed (4800 or 9600) of the serial comms links many receivers use worried me and I know that several that are ostensibly USB actually use a USB/Serial interface internally and so are just as bad. I noticed that to get round this the NMEATIME2 shareware uses a Kalman filter to filter NMEA arrival times and manages to get an accuracy down into the single milliseconds.
I’m told – would have to check old emails for detail – that the 1pps is very accurate long term (so count 100 pulses and the average interpulse time will average very close to 1000ms) but the individual arrival time of a pulse is still somewhat dithered – on some hardware.
Can dig out the emails if you are interested.
So, on eclipse day you were in a jeep too Martin. We were in the back of a jeep driven by the operator of the 88″. Woke to pouring rain and no hope, but the guy – who could have gone to the top of Mauna Kea (being observatory staff and able to get past the police cordon) if he hadnt stuck with us – went to the saddle road and waited.
Managed to see it through fog – so stuff all corona apart from prominences but binoculars showed the structure in the inner corona despite the fog. No Cat Stevens (happily) but there was a burst of Robert Plant’s Manic Nirvana before we left base in Hilo that morning.
Just an update: I have been out with the RASA on two nights so far – 11th and 13th – and not yet had trouble with dew forming on the corrector plate – even in the absence of a shield. Hiwever, neither was a wet night (it was -1C and -5C respectively) but there were hard frosts (really hard last night). Will update again when I have used it on a night when water is running off the mount or pier.
