hughgilhespie

Hi Peter, I've been looking at your 'final' schematic again and I think you MAY need to add pull-up resistors to make it function in the way you need. A bit of background. The digital outputs from the VM110 are 'open collector' outputs. When they are switched ON by the Lesvedome software, the output terminal is connected via a LOW resistance to ground. When they are OFF, they are still connected to ground but this time via a very high resistance. What you need is a way to convert this resistance change into a voltage change to operate your relay board. You get the necessary voltage change by using a 'pull-up' resistor connected beween the digital output terminal and the positive supply. When the resistor is in place, when the DO is OFF, it's potential is pulled up to the same as the positive supply. However, when it turns ON, the voltage at the output terminal drops to very close to zero as there is a low resistance path to ground. The combination of the pull-up resistor, say 5000 ohms and the on-state low resistance, say 1 ohm make up a voltage divider of total resistance 5000 + 1 ohms. In the on state, the output voltage is 0nly 1/5001th of the positive supply voltage. The reason I say you MAY need to add a couple of pull-up resistors is that the relay board MAY already include these resistors. The relay board uses optical isolators so the input circuit is something like this: Please note - this is just my guess and it might be wrong. However, if it is like this then you already have a suitable resistor, the one I have called Rd. To make this circuit work, as well as connecting the IN- terminals to the Velleman digital outputs, you will need to connect the relay board IN+ terminals to your +12 volt supply. Then when the software switches the Velleman output to ON, current can flow through the light emitting diode in the optoisolator on the relay board. This triggers the matching phototransistor and activates the relay coil. Bingo!! There is one other assumption here - that the DC supply to the Velleman board and to your relay board share a common ground. I am sure this is the case so this will work. I am sorry if this is too confusing but I think you will need to experiment - if the relay board comes with a schematic then you can easily see what you need to do. If not you may have to experiment. In the latter case, I strongly suggest that you NEVER connect the positive line 12 volt supply directly to the IN+ relay terminals. Always use a resistor in series with a value of between 1000 and 10000 ohms. (Because if the resistor I called Rd doesn't exist you would immediately burn out the photodiode in the optoisolator) Regards, Hugh

Also, I forgot to say that the free program, WakeOnLan from Aquila Technology works very well https://wol.aquilatech.com/ . You need the MAC address of the remote machine and you have to make sure that WOL is enabled on the remote - loads of U-Tube vids to help here. Regards, Hugh

Steve, When I use Windows RDP I shut down the remote machine by pressing the Alt + F4 keys, then selecting shut-down from the options given. Works a treat! Regards, Hugh

Hi Peter, I have been away from this topic for a few days but it seems as if you are making good progress. One thing that occurs to me is that there seems to be a bit of confusion about the power supply of the VM110 board. The board is actually powered by the 5 volts from the incoming USB connection. The chip on the board that runs everything is a PIC18F family processor that actually runs at 3.3 volts. For reference, I have attached the construction instructions for the K8055n self-assembly board. This is actually identical to the VM110 board. The instructions include a circuit diagram for the board on page 15. This shows the 5 volt supply from the USB socket and the 3.3 volt regulator to supply the PIC chip. So the important thing to realise here is that you need to be sure that the Raspberry Pi that the VM110 is connected to via USB can supply sufficient current to run the VM110 board. I don't have any experience with RPis so I can't help you there. Next is the confusing CLAMP connection on the VM110 board. This does NOT supply any power. It must be connected to the EXTERNAL +12 volts (or whatever voltage you are using) and it's function is to protect the ULN2803a chip against the high voltages that occur when an inductive load, such as a relay coil, is switched on and off. The ULN2803a chip is a buffer/signal level shifter chip and the VM110 board uses two of them. One for the digital inputs, DI 1 to 8 and one for the digital outputs, DO1 to 8. I have attached the Texas Instruments datasheet for the ULN2803 chip and also a sketch showing how you need to connect the digital outputs. Basically, the digital outputs are like electronic switches. One side of the switch is connected to ground and the other side is connected to the appropriate Digital Output terminal. The thing that you are switching on or off (relay coil or whatever) has one side connected to the DO terminal and the other to the EXTERNAL positive voltage supply. This can be any voltage up to 50 VDC. When the switch 'closes' there is a low resistance path for current to flow from the positive supply, through the load and then to ground. So, for your case, the relay coil becomes energised. When the switch is 'open' there is no path to ground so the coil doesn't become energised. Actually there is a very high resistance path and a microamp or two does flow through the load but nothing like enough to energise the relay coil. As I said in an earlier post, the current through the each of the loads being driven by the chip can be up to 500 milliamps - subject to a total of 2.5 amps at any one time . HTH Regards, Hugh k8055n_Schematic.pdf uln2803a.pdf ULN2803a Darlington.pdf

I usually upgrade my Windows 10 computers to Windows 7.

Hi Peter, Many thanks for the detailed explanation of what you are trying to do. I have no experience with Raspberry Pi's and their software so I can't comment on your proposed wifi link but as it is tested and working I am sure it will be fine. So, if I am understanding correctly, you will install the VM110 board and the associated relays in the rotating part of the dome alongside the existing Rigel kit. Then you will have some sort of master switch that will allow you to use either the Rigel system manually or the Lesvedome software remotely to control the dome rotation - and hopefully - the shutter opening and closing at a future stage. More questions I'm afraid. As far as I know, most people who implement the Lesvedome system use the Charles Harrow schematic with 6 dpdt relays. Is there a particular reason you are using an alternative circuit? The Harrow design would give you all the shutter control circuitry for the future. From my own (bitter) experience I can tell you that it is MUCH harder to try and modify things later than to try and include everything you might want from the outset. Next the Bourns encoder. I am sure you know this but the VM110 board can only cope with a relatively low pulse rate from the encoder. The pulse rate of course depends on how many times the encoder turns per dome revolution and the dome rotation speed as well as the inherent ppr rating of the encoder. For my Pulsar set-up I needed an 8 ppr encoder. Anything above that was too fast for the VM110 board. I would strongly suggest you do NOT use a Hall effect sensor for the home position sensor. These sensors have a high level of hysteresis and are not really suited to position measurements An optical switch would be much better. I used an Omron EE-SX3009-P1 switch. This came from RS I believe. This switch has a slot with an IR light emitting diode on one side and a phototransistor on the other. When anything interrupts the light path it triggers the switch. As the slot width is only 5 mm wide you are guaranteed a home position accuracy to better that 5 mm. As Alan explained, these switches, like the Hall effect switches, are active devices and need power connections as well as the switch output. The switch that I used operates at 5 volts as does the Bourns EM encoder. Bear in mind that you will need a suitable 12 volt to 5 volt converter to power these. Again, there are hundreds of suitable small buck-converters with screw terminals on fleabay. How you actually make the stuff depends on your level of experience. My method (a very basic method indeed) is to first decide on what modules are needed and to get their dimensions. Then I do a drawing (I am very old so I use Microsoft Visio) that shows all the modules and where there connections are. Then move the modules around on the drawing until I have some sort of reasonable layout. Then I add the wire runs to the drawing. The idea is that you end up with a layout that can be made by screwing everything to a single sheet of Aluminium. Obviously you need to make sure that the aluminium sheet will fit somewhere in your dome. A quick aside - I had a horror of drilling holes in my Pulsar, so I mounted everything on plywood panels that I glued to the inside of the dome. I use CT-1 construction adhesive, very good stuff! So, I suggest that the next step for you is to finalise the design as best you can. Step 1 : Which circuit will I be using? Step 1 : What modules do I need? Generic at this stage, e.g. a relay module, a power supply module, VM110 board, master switch module....... Step 2 : Decide on the actual components - which relay module? which power supply module? .................. Step 3 : Best thing is to actually buy them but if not get hold of the dimensions somehow. Step 4 : Work out how big your base plate can be and what size it will be then do a drawing of the shape. Step 5 : Add simple drawings of all the modules and where there connections are Step 6 : Fiddle about for hours moving things around until you're happy then add the wires / connections to the drawing. Step 7 : Buy a bit of aluminium sheet - hopefully already cut to size - drill the holes to mount everything, and .... Step 8 : Make it!! I know this is all a horrible over-simplification but it really is doable. Let us know which circuit you want to use and I am sure we can come up with some more definite help. Regards, Hugh

Hi pmlogg, I am happy to help you if I can. However, there are a few questions that need answers so that you get the best help. First off, are you actually going for a 'full' Lesvedome / ASCOM interface or just a manual solution for your dome rotation? The second question is what sort of motor will you be using to rotate the dome. The choice of motor will determine what relays are suitable. The good news is that the digital outputs from the Velleman K8055 board are buffered by a ULN2803 chip. This will handle relay drive currents up to 500 mA and voltages up to 50 volts which would be sufficient for driving almost any low voltage relay. The ULN2803 also incorporates protection diodes and the outputs can be connected directly to a relay coils. However, be aware that the power to drive the relay does not come from the Velleman board. You need to connect the Velleman 'Clamp' terminal to your own power supply. There are literally hundreds of board mounted relay modules that come with screw terminals. The choice will depend on the current rating needed for the motor. To implement the circuit you have shown, a board with 4 spdt relays would do nicely. This https://www.ebay.co.uk/itm/Mini-4-Channel-DC-12V-Volt-30A-Relay-Module-Control-Board-High-Low-U0P3/113195531357?hash=item1a5afabc5d:g:OuoAAOSw441bCEZX is a 4-channel 30 Amp relay board that is the sort of thing that would work for your application. Let us know the answers and we can offer some more focused advice. Regards, Hugh

Hi Francis, I use an OTA mounted set-up that works well - at least as far as I am concerned. The kit I am using is a combination of a cheap-ish mini-computer [Kodlix GN41, about £99 from Amazon] with an expensive Pegasus Ultimate power-box [An eye-watering £500]. I am running all Windows software - the Kodlix comes with Windows 10 Pro fully licensed pre-installed. It also works with a 12-14 volt power input that suits my set-up. I have attached a schematic of how everything hangs together. I use EQASCOM / SGP /CARTES DU CIEL for image acquisition and everything is controlled remotely using Windows Remote Desktop Protocol. I can power-up the OTA computer using Wake-On_Lan so in theory I can have fully remote imaging. I don't do this - I am much happier getting everything going whilst I am present and then leaving it running. The big advantage of using the Pegasus box is that it combines a powered USB2 hub with a focus motor driver and dew-heaters. I have only 3 cables from my mount. A 14 volt power supply, an Ethernet cable for Wake-On-Lan and RDP and a USB2 cable that connects to my observatory dome driver. This summer I am intending to replace the USB cable with a wireless connection to my dome driver hardware. I will also experiment with how well the RDP link operates with wireless instead of the existing Cat 6 cable. If successful, I will achieve cable nirvana - only one power cable to the mount and everything else either on-board or via wireless. Well nearly - I don't think I could start the OTA computer remotely without having the Cat 6 cable connected, the Kodlix does not do 'Wake on Wireless LAN'. As I am in the obsy to start things anyway it shouldn't matter. As you seem to have various options for scopes and cameras, it would be a nice idea to have a removable assemble with all the bits - computer, hub, etc, that could be swapped between rigs. My setup is not quite so flexible. I have everything attached to the tube rings that hold my scope and dismantling is a bit fiddly. If I started again I would do it with the single, removable assembly. Hope this helps, Regards, Hugh USBNet_Rev2.pdf

Hi Aidan, What are .heic files? My Windows computer doesn't recognise them. Regards, Hugh

Hi @Carbon Brush, I think you have the decimal point in the wrong place. Linear expansion coefficient is 13 ppm per degree C. 10 degrees change gives 130 ppm expansion 1000 mm focal length is 1 million microns So, 10 degrees expansion is 130 microns = 130/1000 = 0.13 mm. Just for interest, using my 530 mm focal length Tak, I need to refocus every 0.5 degrees change to keep the focus in the critical zone. So, most of the focus change with temperature is something other than the thermal expansion of the metal. HTH Regards, Hugh

Come on Steve, admit it! You photoshopped it!! ? Regards, Hugh

Zenith sky brightness information Coordinates SQM 21.73 mag./arc sec2 Brightness 0.220 mcd/m2 Artif. bright. 49.1 μcd/m2 Ratio 0.287 Bortle class 3 Elevation 154 meters Not too bad in North Devon! As well as the Sky Quality I have also done a quick check on the Sky Quantity and as far as I can tell it goes all the way around the house and all the way up too. Happy New Year to all Regards, Hugh

Hi Dave, Try https://www.leespring.com/uk_index.asp Good range and order online. I have used them quite a bit. Regards, Hugh

'So, now i've got my CNC kicked into shape, it's time to start my 14" dob build. I've had the optics since i was 21... i'm now 52 HAHA so yeah...' I am so relieved - it's not just me then. I've been sitting on a 12.5 inch conical mount mirror from R F Royce and a matching carbon fibre tube for the past 5 years. OK, it's not quite so extreme but I still feel the guilt. My mirror cell is also about 80% complete. One day............. Regards, Hugh

Good point! Skywatcher mounts are also a bit picky about input voltage. I run my set up with a nominal 14 volt supply that becomes about 13.2 - 13.6 volts at the Pegasus hub I use. However, when I was looking at choice of mini computer to mount on the OTA, quite a lot of the options specified 19 volts - this is a sort of standard for laptops. When I queried the manufacturers, none of the ones I asked said that their machines would work on 12 - 14 volts. So, choose carefully and check, check and check again! Regards, Hugh

Hi Steve, Another late entry to this thread. You don't say what sort of mini-pc you will be using or how it will be attached to the imaging set-up However, I can strongly recommend that you get a 12 volt powered mini-pc that you can attach directly onto your telescope. Also, while your attaching things, consider adding a USB/Power hub - think Pegasus or Hi-Tech Astro. That way you can have almost all your cables actually on the OTA. The only dangling cables would be your network cable and a DC power cable to the hub. Regards, Hugh

+1

Hi, Really good write up - thanks! I had a similar experience with my Pegasus UPB in that when I connected it to my mount computer, the computer wouldn't accept other USB inputs. At that time I was using an old EQDir cable with the Prolific chipset. I replaced this with a new FTDI based adaptor and as far as I can tell everything now works as it should. However, I do use the Pegasus USB hub in preference to the mount computer so my EQDir does come from the Pegasus hub. As everything seems to work, I haven't really done any more testing so this is far from definitive but I suspect the problem was more to do with the old EQDir cable rather than the Pegasus. HTH Regards, Hugh

Or in my case, to move a little piston up and down......................

OK, Windows sucks! Now then, lets have a go at Linux. Let's see I think I'll try..................... Elementary OS, Linux Mint, Arch Linux, Ubuntu, Tails, CentOS 7, Ubuntu Studio, Open SUSE, Fedora, Bodhi Linux, Mageia, Kubuntu, Mandriva, Deepin, Budgie, Ubuntu Mate, Sabayon Linux, Crunch Bang Linux, BackBox, SolydXK, NixOS, KaOS, Pinguy OS, Peppermint Linus OS, Ubuntu Kylin, AV Linux, Scientific Linux, Alpine Linux, aptosid, Russian Fedora Remix, Kantofix, Lunar Linux, Void Linux, Grml, Caldera Open Linux, Parsix, TurnKey Linux, LliureX, Yggdrasil Linux, VyOS, Debian Pure Blend I got bored at this point. Is it really any wonder that even people that would like to try Linux give up!

There are some really good books on learning to use a lathe. Genuine guides for beginners that get you started. I taught myself in my sixties - at least to a level that gave me enough skills for my own needs. I have never seen any books that could do that with Linux. Regards, Hugh

Hi Matthew, Just a note of caution here. Using RCA connectors soldered to Vero board is NOT a good idea. It takes a fair amount of force to insert and remove the RCA plugs and all that force is being held by some very thin copper strips. Sooner rather than later the connector will come adrift from the Vero. It is a really good idea to use chassis mounting connectors and let the box or whatever take the strain. I know that there is an enormous amount of equipment sold that have the connectors soldered directly to the pcb, I have some myself, but that doesn't stop it being a very bad design. If you intend to mount your circuit in any sort of a box, then for the sake of drilling a hole or two in it, you can have much improved reliability. HTH. Regards, Hugh

I am so pleased to read these posts!! I am a total beginner at using SGP and I experienced exactly the same behaviour yesterday - a very uninformative error message. Naturally I assumed that this was me doing something daft. I spent hours uninstalling, reinstalling, watching Jared's you tube video, etc. And then - IT'S NOT MY FAULT!! Phew, Hugh