- This topic has 1 reply, 2 voices, and was last updated 8:44 am on 2017-01-09 by patbunn.
January 7, 2017 at 10:17 am #115852
Richard S. Wright Jr.Senior Moderator
I have been preaching the merits of the Raspberry Pi for mobile/portable imaging for a couple of years now. TheSkyX Pro is now officially available for Raspberry Pi (as well as Linux), and I'm really gratified that all the hot air I've been putting out has turned out to be something more than just hot air. Quite a few people are picking this up, and many are following my original model which is putting the device on the mount. But there is also a great deal of interest in putting the little guy in the observatory and accessing it remotely, either in the house or in a warm room many yards/meters away. One of the biggest stumbling blocks to this in the past has been getting a reliable USB extender to work with all the devices. Furthermore, unlike the “it just works” past of Mac OS X, Apple users seem to be especially penalized in this regard with the latest OS updates. An exchange on the support forum inspired me to write this blog as it might be of interest to many others as how I accomplished this myself.
My setup seems to be quite typical of many backyard observatories, with the only exception that it is transplanted to a private astronomy community in south Florida. I have a SkyShed Pod to protect my mount and scope from the elements, and a “normal” shed nearby that serves as storage, a warm/cool room (and in Florida, a refuge from the bugs), as well as a dormitory for spending the night. This ensemble is my “spaceship” that I dreamed of as a child in some ways. I come down and stay a few nights at a time, so this is only quasi-automated. Typically I'd sit inside the dome, but sometimes the weather or mosquito air force makes this less desirable, and so now I've used a Raspberry Pi to make the dome “remote control”.
Other than opening up the dome to the sky, I can now run everything from a computer several yards away, and I did it with a buried Ethernet cable, but no USB extenders. Instead I put a computer in the dome that is running TheSkyX, and I use remote desktop to access it from my warm room. Your warm room could be your den or living room, or if internet access is available it could be anywhere else in the world for that matter. This is nothing that hasn't been done 10,000 times or more by others who access their observatories remotely. The only difference is, instead of a dedicated laptop or desktop computer left in the dome, it's just a small computer the size of a deck of cards to which everything is plugged in to. It is also running a variant of Linux and there is a zero percent chance that it will reboot in the middle of the night for “important updates”. Since this is dedicated to nothing other than running my observing sessions, there is also zero need for me to _ever_ update the OS. No updates that will break compatibility with drivers, etc. etc. Well, I'm getting preachy here… so let's get to the details.
The mount is a Paramount MX+, and I run a USB cable from the mount to the Raspberry Pi, shown here in a sealed box along with some other electronics I'd like to keep away from the plague of frogs that likes to invade my dome from time to time. On the mount is a 12″ imaging newtonian from Sky-Watcher, for which I've replaced the stock focuser with a Feather Touch. You can see the Focus Boss controller also next to the Pi. The blue cable is an Ethernet/RJ45 that I ran up through the mount to the PosiDrive motor on the focuser. The controller needs power, and then the USB is fed right into the Raspberry Pi right next to it. The red cable coming from the Pi is Ethernet running out the bottom of the dome, through a buried PVC pipe to my control room.
The camera is a Starlight Xpress Trius 694 monochrome camera, which convieniently has a built-in powered USB hub. So the Lodestar guider, and the filter wheel all plug into the camera, which is then connected to the mounts USB on the versa plate. Power for the camera and dew controller are also routed up through the mount.
This would be a good time to show you my mad cable management skillz (sic)… Hey, it works! Yes, I velcroed the dew controller to the filter wheel. Why not?
Aside: Dew is my greatest enemy in Florida, even more so than the tiny tree frogs that like to crawl into EVERYTHING. I thought a friend was crazy, but it turns out a dew strap at the rear of a newtonian does keep the mirror dry longer. I also put a small dew strap in front of the secondary mirror and run the power cable along one of the spider vanes.
Two power lines, an Ethernet cable (to the focuser), and a single USB head back to the versa plate at the rear. I'm a little embarrassed by this, but I think it's typical of what anyone can do “at least”. No dangling cables to the ground, everything through the mount. Another confession… running the blue Ethernet through the mount dislodged one of the homing sensors. We all do it! I had to remove the dec cover, and reseat it… and we were good to go again. It's amazing how many wires it takes to string all this stuff together!
Now, about the Raspberry Pi. It's a Raspberry Pi 3, with a 64 GB Ultra fast mini sd card. I put the latest Raspbian Jessie Pixel on it, and of course installed the latest version of TheSkyX Pro for Raspberry Pi. I disabled both Bluetooth and Wi-Fi because I wasn't going to use them. RealVNC comes already installed and configured now, and it was set for a static IP address all ready to go. I also installed SMB, so I could setup the folder used to save FITS files in as a network share. This makes it easier to get the images off the device without having to go out and physically access the Pi with a jump drive. Just drag and drop… and typically, I watch the files come in and sometimes play with the data with PixInsight as it does so. There was a trick I had to employ to get VNC to serve up a full resolution desktop when no monitor was connected. Bring up a terminal window and edit /boot/config.txt
sudo nano /boot/config.txt
(that's how I edit them anyway).
You need the following three lines uncommented (remove the #'s)
You will have to reboot for these to take effect. It's best to do this all indoors with a real monitor/keyboard/mouse plugged in. These frame buffer width and height settings will of course also have effect for real monitors. You can make this smaller if you don't need this much screen real-estate.
On the other end of the Ethernet leading to the Pi, I have my MacBook Pro. The Pi needs a network to show up on it's Ethernet port before you are going to be able to get into it, so you either need to share your Wi-Fi network connection over the Ethernet or create a local network, and include the Ethernet. You could of course also go crazy, have a router, your own LAN, etc. It's easier and simpler for me to just join my local area Wi-Fi, and share the connection on my Ethernet port (easy to do on a Mac… still some things are easier here .
To get to the Raspberry Pi, I installed a free VNC viewer for the Mac, just about any VNC client will do except (oddly?) the built in screen sharing capabilities of the Mac, which is actually built on the VNC protocol. On the mobile front… I do use the Wi-Fi on the Pi, and you can connect with an iOS or Android Tablet this way.
An important note about date/time. If you're sharing an Internet connection, the Raspberry Pi (after some small latency) will update it's date/time from an Internet time server. If you create your own network, this will not happen, and since the Raspberry Pi does not have a built-in hardware clock with a battery backup, you will have to set the time yourself. Do this on the command line:
date -s '2017-12-25 12:34:56'
I'll leave it to you to decode the format above… BUT it's important to note that this is UTC or GMT time, not local time. TheSkyX if you setup the location correctly with Time Zone information will show the correct local time for you after doing this.
Shown at right is a real screen capture from a real imaging run just the other night. I was doing 15-minute guided images of the Horsehead nebula in Ha (there was a little moon up). I used @Focus2 to focus, and I used TheSkyX's guiding and image acquisition. The guider graph is pretty text book for a Paramount without a PEC table (I recently lost my PEC table due to industrial espionage… well, not really, but it sounds a lot better than the real reason I need to retrain the PEC on this mount
This is also a good example (while we are here) of what the real world often looks like. Those two “hot pixels” near the guide star are nothing of the sort, they are just bright because the screen stretch is adding contrast. They might actually be a little “warm”, but they are not affecting the guide star at all (in fact, I was using the new Heuristic hot pixel removal feature that is currently in the Starlight Xpress plug-in). Also, note that off axis guide stars are not always round, and this one actually has tell-tale signs of the diffraction spikes. This also does not adversely affect guiding. Finally, the RA graph (top most) looks terrible, “my RA is all over the place”. No it's not. There is a clear rhythm there, it's the periodic error. It jumps compared to Dec.. nope, DEC is jumpy too, that's just from seeing. The RA graph looks just like the DEC graph, except it's moving up and down with periodic error, and it's making corrections, which makes the seeing appear to be moving more than it actually is too. Note my aggressiveness is turned way down, and I'm getting perfectly round stars on my image.
I might be getting to be a crotchety old man, but it seems to me that todays consumer operating systems are more and more about entertainment, optimizing your shopping, or making it easier to post vacation photos to Facebook. When it comes to getting “work” done, I'm becoming more and more a fan of Linux, and especially of a dedicated computer. In a sense… the Raspberry Pi in this scenario is an “imaging appliance”. If you want a little more horse power, or you want to run PixInsight or a few other higher-end utilities, you could always put a dedicated Linux machine in the observatory as well. I think we are at the beginning of another shift in this business… stay tuned and see if you don't agree. There is just…. this one more thing… we need to do for people still relying on the Windows ecosystem….
RichardJanuary 9, 2017 at 8:44 am #239630
Amen to the “this one more thing”
When you say remove the numbers on the uncommented 3 line – what exactly are you saying to do?
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