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# Ajohn

Members

783

1. ## Painless remote control options

The ethernet cable is pretty clever actually. It designed in a similar fashion to the co axial cable that is used to carry radio frequencies such as analogue television signals from the aerial. There is some info on the subject on the wiki https://en.wikipedia.org/wiki/Transmission_line This should talk about distributed capacitance and inductance along the line because that is what makes them work. In other words some values per unit length after a fashion. If this isn't done all sort of strange things can happen. Even the actual resistance of the wire plays a part as it can help damp out the signals travelling along the line. Fourier comes into this where the square waves typically used in digital transmissions are considered. The rising edge is made up of a harmonic series of much higher frequencies. If these aren't preserved there can be overshoot, undershoot or even ringing or nothing at all coming out of the other end. Signals can even reflect back from the part that receives them. The reason solid cored cable can carry signals for greater distances is probably down to controlling the parameters as it's made and more importantly something usually called the skin effect. DC uses all of the diameter of a piece of wire. As the frequency goes up the current levels get more concentrated towards the outer areas, this effectively means that it's resistance increases with frequency. Useful in the transmission line area as it means the wire diameter can be used to control the resistance. Resistance offers a good way of controlling damping - how well a rising edge on a square wave is preserved along the transmission line. I'd guess they under damp. In other words a rising edge over shoots and a falling edge undershoots. I can't find any pictorial illustrations on the web but all of these factors combine and limit maximum cable lengths for some specific design of cable. Me - well I can believe that splicing ethernet cable into a usb cable might increase the maximum length that can be used. I wouldn't take it as fact though. The person that posted this was an amateur radio person - they generally will understand the above and be well aware of the factors involved. On USB 3 it wouldn't surprise me if fibre optic cables become more common over time. John -
2. ## Replacement Pluck Foam for Maplin Flight cases

I use the cases and enclosures site too. I've had several off them. Nice prompt delivery and for the price decent quality as well. I found them via ebay. I enquired about some from a seller on there, didn't buy and soon after received an email complete with a discount offer. They do that every now and again. I just bought a case of them that should take all of my eyepieces and another for an 80mm APO I bought recently. The fact that they give a full list of sizes helps but remember that some of the dimensions in one direction will include the lid which will be lined with dimpled foam. Another make that can be found on ebay at times is called something like skelington. They are dearer but still not too bad in large sizes. Thanks for the foam link. Haven't checked on that one but I often find that the foam costs more or less the same as the case when bought separately and the ? skelinton ? is in need of a new insert. It hasn't kept up with my camera gear so may as well use it for something else. John -
3. ## Painless remote control options

It looks like there are other INDI like solutions. I was hoping to get some links like this when I originally posted. http://sourceforge.net/projects/iastrohub/ http://maxchen.im/tinyastro/en/ Both of these seem to be extremely low power and very portable - no pc level power needed at all. I was glad to see that on the first one jpg's are downloaded and raw left in the camera. While viewing in FIT's etc may be attractive it's a hell of a load from a dslr. That way download speeds get fast. Many cameras put rather a lot in jpg's these days anyway. That can be increased on some cameras via various settings. I would say the biggest problem with these is that they use a very commercial device rather than 'pi etc. It seems to make a huge difference to plat solving times. Only problem is that I followed a link to one and out of stock. It's probably been superseded and always will be from time to time with different parts. John -
4. ## Painless remote control options

Is that solid or flexible cat 5? Some people on the INDI forum have swapped to an Odroid. Best read if interested. One of them is running the Kstars end in a VM on a Mac book. It could be an Odroid or 'pi on the other end. I ordered an Arduino board yesterday after seeing the INDI focuser. I have had a long break from software after all. Last time I looked at this sort of thing it needed too much kit. John -

6. ## Wireless dimmer for LEd strip, will it work?

t should work as these sort of things tend to use pulse width modulation. In other words the switch at some frequency with a variable on time. You can also get manually operated ones that work the same way. Some people use those for controlling the light intensity when they convert microscopes to LED lighting. The current rating on these is more or less the same so I'd guess the radio controlled ones use the same switching electronics. John -
7. ## Painless remote control options

There are usb to ethernet extenders about. I thought that the link I posted was to one but that turned out to be incorrect. These do convert or maybe just drive ethernet cable usb style - there was a post somewhere that reckoned they had extended one by simply splicing cat 5e cable into an ordinary usb cable that had been cut in half. Other things could be going on though. Most of the extenders state usb 1 some say usb 2 compatible, some usb 2. Personally I'm not sure if usb 2 devices will drop to usb 1 in much the same way as ethernet drops speed if it can't be maintained so I see these things as being a bit dubious. Any built in chip could force USB 1 anyway. If you search ebay for usb extender several are listed. The length of cable they will drive varies. There are also active usb cables that use a chip to receive and boost the signal taking power from the connector, some have a separate power supply. Lengths vary again. While watching a pretty awful spaghetti western 1/2 hr ago I realised that while the powerline ethernet adapters look great they probably don't have gigabit lan drivers in them so data rates may be 100mb/sec in practice. That seems to be the limit for a 'pi anyway. The Odroid does seem to be gigabit and will run the software that interests me personally. Same price more or less but people seem to be having problems with INDI and wifi at the moment. However as powerline could be a private network, nothing else on it, it might turn out to be the fastest option even at 100mb/sec. It should be possible to treat the 4 USB ports on the new 'pi effectively as a hub so there isn't any reason why something shouldn't go in one and be split off into others but 100m USB cables appear to have their problems. Some suggest that the active ones can be daisy chained but if so why do some have separate power supplies. As some one pointed out earlier cross compiling does seem to be the only "dev kit" available in practical terms. Having seen what INDI and Kstars/Ekos can do I don't think I need to write any software at all -. other than I will wonder why they haven't put their remote focus in it as well but that may be down to the number of timers in the processor. If some one uses windows and wants to work in Linux it should be fine working in a virtual machine. I have done that in the past the other way round but not for a long time, My biggest concern in this area is if Kstars/Ekos will run on a decent netbook. I've always intended to run a Linux on it but since iPad it's just been lying around. In this case I don't need a long cable - I only need that to run it all from my desktop. Maybe perusing that via vnc on something else at times. According to the wiki the ethernet cable length limit is 100m which can include some flexible. Like most things I'd guess it could be longer but 100m with decent cable should work 100% and not drop packets. I'd guess that the camera usb ports place another limit on max speed. While they may be usb 2 this doesn't mean that they have to send 480mb/sec continuously, just pulse at a rate they can manage. Bit like what ISP's do to our connections. I haven't downloaded from a camera this way for ages as direct from the card was much quicker. Guess i had better try that and find out. This might seem all a little strange but I want the option to use it all close to the scope and away from home - ie portable. This rules out using watty parts close to the scope for me anyway. John -
8. ## Painless remote control options

I've just come to the same conclusion Mike. 500mb/sec ones can be bought. It should even be possible to use a remote usb hub with these plus the ethernet to usb adapters. There does seem to be some USB2 ones about but I'd guess that would mean actually buying them to find out. I'm after something portable rather than fixed otherwise I would probably just run an ethernet cable. Having seen the UK price of reinforced cable I would probably bury it in toolstation hose pipe if I did that. In real terms I will be using an extension lead plus the powerline units and a dslr which is why the bandwidth concerns me. On that score the Odroid looks more favourable than a 'pi. It's an interesting area to look at. The manufacturers are producing chips to actively boost usb 3 because the max lead length is so short. There are also some fibre optic usb 3 leads about as well but the prices are a bit high at the moment. Even a fast usb wireless standard but no one seems to be doing anything with it. At 10ghz it will probably only work over short distances anyway. Only remaining problem is Altar Astro. I ordered a light weight mount off them specifically for this and expected them to get in touch if it wasn't in stock. Not a peep out of them even after a message on their answer phone. John -
9. ## Painless remote control options

It reads to me that the server side must be Linux based, 'pi etc, but the client side can be windows, linux, mac or android. I became a little curious and found there is a cross platform usb library about that can be run in and used in user space. It's likely to be very compatible with all kernels it can be compiled for. What it appears to do is standardise the usb interfaces across various platforms so the kernels are still being used. It looks like the latest versions will also handle usb 3. The wifi dongles come in 3 flavours, 150,300 and 600 odd Mbits/sec. The later is only available on USB 3 and run at 5ghz. I believe some step back under certain circumstances and that data rates are upped by using more than one channel. If that can't be done due to use or interference the speed drops back. There are some interesting numbers on here, bluetooth might work out faster than some. the latest is supposed to reach 24Mb/sec https://en.wikipedia.org/wiki/Comparison_of_wireless_data_standards I should add that it looks like INDI can be run via wifi or wire but I haven't really ;looked at the detail. Maybe a sophisticated cable reel and solid cored cable is the fastest option. John -
10. ## Nikon D5100 active cooling

There is an interesting hack post on noise that I have not really looked at closely yet. https://landingfield.wordpress.com/2014/05/13/teaser-nikon-dslr-black-point-hack-for-astrophotography/ Some where around on the same site there is info on modifying the filtering as well. Interesting comments about canon - nikon noise levels. Not sure they are entirely correct as companies make changes from time to time. Eg my E-M5 uses a Sony sensor. Turns out that My E-M1 uses a Panasonic one. Noise levels are similar but the E-M1 seems to have less chroma noise. I believe Nikon use Panasonic sensors from time to time as well. Live view will heat the sensor up - it's being used all of the time. Some mirrorless cameras go to some lengths to only activate it when needed and even warn about that effect when the rear screen is in use. John -
11. ## Painless remote control options

The companies that maintain Linux distro's have a way of ensuring people upgrade - eventually people try to install something and find they can't because things have moved on. I had that happen last week also found I can't update my favourite photo editor -not that I need to do that. Back on topic. There is something about that will link usb over wifi according to one source http://www.raspberrypi.org/forums/viewtopic.php?f=31&t=97179 The person who wrote virtualhere mentions that it's stand alone code rather than using the Linux facilities. That might explain the speed. Not sure. Like most I pull the card out of the camera and plug it into a reader. I haven't used the camera download for a long time but vaguely remember it's slower. It's free to try on one device. Makes me wonder about wifi cards. Interesting demo of remote control here. There are some others on youtube. The INDI telescope end has been ported to a 'pi but there is a 'pi look alike around. Odroid. 1.5khz 4 core and some reports that it's IO is faster. It also has a gigabit lan connection. There is an option to install a different type of flash memory to it as well. Treasure Island Britain makes fibre optics way too expensive as the prices leave a bad taste in the mouth and that's just the cable. John -

13. ## Painless remote control options

There is another way but how to use it ? eg, the page may load slowly. http://www.fiberstore.com/10-100-1000base-t-gigabit-ethernet-auto-negotiation-copper-sfp-optical-transceiver-p-20036.html There are also some that use 2 cables. Others look to be even cheaper but not sure how they connect. There might just be a reasonably priced UK supplier. There are some cheapish dual fibre managed ones on ebay but straight links like the above would be better. Not that I know much about them. Looking further they all use 2 fibres. John -
14. ## The 20 " grind has begun

I'll be brief. It's small 220mm but < F3 for a cassegrain. I'm not sure I will ever finish it. I've completed the design including a corrector for it. That took a while. If I do any more work on it it will be via a machine. I have collected a few bits and pieces for that but too busy with other things. I made a ronchi screen but wasn't impressed. I used something with the same basic design as Texereau's but with micrometer spindles to drive it and adapted to to do x-y type knife edge testing as well which I found slightly easier in some ways when things got close. As a final check I knocked up a Dall null tester. With your problem I wouldn't care about what experienced mirror makers thought, just find out for myself. Many use machines in any case. If I did that I would probably see what laps about 4/5 the diameter of the mirror did. Might be an idea doing it by hand as well mirror on the bottom. 5/6 is supposed to maintain the radius with suitable strokes. Not all that much interest in dobsonians now. A 10in put me off a bit some time ago. I made a hexagonal tube from thin ply with glued butt joints - worked well except I found it wasn't entirely square to the mirror a little too late. John -
15. ## Painless remote control options

That's what the remote hub I posted a link to seemed to be when I first looked. Must have been wishful thinking. Some one posted a link to a device of the type you suggest but usb 1.1 and no speed spec. I've looked for better but so far haven's found much. I'm not sure about max distances but having used a networked PC at work it seems to be a pretty long way with just typical pc gear. I got some people in to wire up an office once. I'm sure some of the cables were over 100ft. Later larger premisses and an IT Dept rather than me plus much longer cables but I'm not sure if repeaters were used. They sometimes do this by using ethernet switch boxes. INDI and a Pi seems to be good option as it can take care of the lot on one cable but that needs looking into. I'll ask a few questions on their forum shortly. The 'pi linked too has 4 ports and i/o pins which I suspect could drive the remote focusing they describe on their site - just model servo motors. I can cope with loading up Linux software, I'm just not keen on writing the stuff any more. The habit dies easily and I have the feeling if I started again I might not be able to stop. The INDI instructions look pretty straight forwards anyway. I have found usb extenders with a spec of sorts, ebay 361045474841. 251378758676 Once the distance goes up so does the price. There is also a lot of USB 1 stuff about. John -
16. ## The 20 " grind has begun

I have a similar problem to you Damain on what has turned out to be a long term project. Mixed designing it and making the mirror. The blank was hogged out for me and despite having done it before it hasn't finished up spherical after fine grinding. Not saying you have that problem but if you do it's best to go back to grinding again. I can tell I have a problem with simple lamp test when the mirror is wet. The image point and the distance at which the movement changes is too woolly. The usual way to persuade a basically spherical mirror to polish evenly is to alternate tool and mirror on top. I feel I would still work that way with a floppy thin mirror. Tool on top is an excellent way of getting a good clean edge and that is also probably the best way to finish off a thin mirror. Either way use say a 1/3 overhang max but vary it and maybe a slight W or V. You'll find mirror on top tends to polish up the centre more especially if off centre but again for a sphere not extreme. The other thing is to avoid getting into a rhythm. Vary the steps around and how much what ever is on top is rotated etc. It's the random aspect that makes the sphere automatically. If it's a thin mirror on top make sure you only apply pressure in the centre - a weight maybe. Once the worst if over I'd also try say 1/2 hr polish and then a much longer press but I'm and old fashioned disciple of Texereau other than mirror on bottom for finishing. He does describe a good way of testing for a polished sphere but it needs an adjustable slit. John -
17. ## Difference between type 3 and 4 Barn Door

The point was making about think arms rather than platforms is that it's easier to make a rigid pivot. One way for instance would be to fit a ball race into a hole in one, few washers for spacers and and bolt it to whatever it pivots on. The 2nd arm needs a sliding contact - ball race again. Another alternative might be the the bronze bushes bearing suppliers sell. The only problem with those is that they are meant to be driven into holes sized to shrink them a bit. It might be possible to buy say ones with a 6mm bore and ream them out to 1/4 in or some similar idea. Bright drawn metal bar is usually pretty close to the stated diameter. Silver steel these days or drill rod as it's called in the USA isn't as close as it used to be. Some supplier stock ground rod. That will be very close. I would be inclined to use 18mm MDF even though breathing the dust isn't a good idea. I have also routed aluminium plate in the past. To add a camera all that is really needed is a small platform on the end of an arm with a ball head on it. I've been intending to do it for some time but ordered the light weight Ioptron mount earlier this week. I suspect I may get annoyed with the suppliers. If they sell it that should stock it / declare delivery times on their web sites. There are probably some better web pages about on tangent arm drives than the ones I posted. It's an old idea but I would seriously wonder about alignment if really long exposures are contemplated and wonder if the complication of the 2nd arm was worth while. John -

20. ## Painless remote control options

I found the page relating to the 'pi autoguider. It's here http://sy2000.blogspot.co.uk/ John -

22. ## Painless remote control options

Thanks Gkec. That indicates that there might be some mileage in what I suspect I will end up doing. There is some OS software around too. More google needed. Nick Morris. A definite option. That is the sort of thing a USB hub server does - just a minimal pc of some sort in a small box that serves usb ports over ethernet. It seems even Maplin sell one. They can be rather expensive but I'd guess those will serve multiple users at the same time. It should be an option on all OS's but I'll bet there are no drivers for Linux which is what I run. On other comments relating to windows home I would have assume that VNC can be installed on anything but the way I would like to do it the USB ports will look as if they are actually on my PC. No remote desktop involved. There is some Pi stuff about but I've not looked that hard and have seen comments about video bandwidth if it tries to do anything with it like autoguiding. There is a demo on youtube somewhere but no details, just autoguiding I suspect. Another set up is shown here. http://www.brahmand.me/astropi/ I forgot remote focus but then thought hang on, dlsr's have magnified live view which might help a little. A 'pi might be able to handle a number of usb ports via a separate hub. Maybe there is a board with lots already. Ethernet can also be sent down a mains cable but I've not looked at bandwidth. There was a reason I posted in DIY. I feel things like VNC and Teamwork belong some where else but maybe not as any suggestions are welcome. John -
23. ## Painless remote control options

I've been nosing around the web looking at things like Rasberry Pi autoguiding and things like that. I'd appreciate any links people have on that subject or anything similar relating to telescope control. There doesn't seem to be single source of links and hours on google bought up the starynights posts and a couple on here eventually but it's slow going. Thinking around the subject - Laptops have the USB ports etc but not wanting to get cold I have wondered about another approach. Basically using a USB to Ethernet Hub Server at the scope. I would be inclined to run a cable to what ever I was using to drive it. 50m cables don't cost much, longer than that and cable and a crimping tool might work out cheaper. If I wanted to be close to the scope all that would be needed is a shorter cable. If I remember correctly even my netbook has an RJ45 socket. Probably another length as well if I drove the car somewhere. Some might favour wifi but I'd guess something could be plugged in to handle that. Anybody tried this or have any thoughts? I've not really tried imaging but as I see it I would need 4 ports. Fortunate as that is what is about at reasonable cost. Webcam, Camera, Autoguide Port and Handset probably with the usual irritating RS232 socket. One other thought was that Linux boxes used to be used purely as firewall routers when people mostly wired things up. Any old PC could be used even a 486 I believe as it didn't have much to do. This could be something a Rasberry Pi could be persuaded to do with adequate bandwidth. I would be ideally connecting up to a Linux box but chances are that any sort of hub might have linux in it anyway or maybe it's some form of ASIC or specifically written software as that would probably be cheaper in the long run. I make some really weird typo's at times. I've checked but ................ John -