My astronomy project:
Battery box and astro server
1: Introduction to battery box and astro server
After struggling for a while with loose power connectors, and poor battery life I decided to rebuild the original parts to be a little more functional. There's nothing so frustrating to be standing there in the night and debug under a clear starry sky. When I plane for this I also draw plans for a local telescope astro server for remote control over WIFI, in principle. Here are some pictures of what is ready to date and a brief description:
Here is a snapshot before the battery and the computer will be fitted in the box.
The choice of the battery fell on a 45 Amph car lead battery as a compromise between weight and capacity, purchased at auto parts store for 50 Euro. If it will be of enough capacity? It will probably be a little problem, but considerably less than the 17 Amph I had before. Those parts above are to be built into an appropriate box later, to protect against moisture and cold. One bad thing with this solution is that it becomes two computers, they connect to each other through a local network at my site and might also have charging current to the telescope so that the battery is not the limit for how long the photography may last. Battery's no disadvantage to have at the telescope anyway when it acts as a backup at power loss. Main switch and fuse terminal is not in place in the picture above. Cables area are 0.75 mm2 or 3.0 mm2 together. Computer has a 7 Amp fuse and the other 5 Amp fuses. Protects better than having one large main fuse.
It is very easy now to charge the battery, with the charger followed a cigarette lighter plug that I plug in one of the sockets. This charger gives only 2 Amp so it's no fast charging. But in the cases I have access to electricity it can be connected all the time when telescope is in use. It's just that it does not give too much interference. If I always had access to 230 volts of electricity and with a bit more powerful charger so it would have sufficed if the battery has been on 5Amph and only then served as backup for a hour. Small and compact, will fit in the box.
How many have not had problems with loose power cigarette connectors withdrawal? Here they are replaced with 2 pin connectors, are to some extent protected against water. Purchased at Swedish Biltema. The parts are connected here is EQ6 mount and camera (Canon EOS 5D). As a complement, there is a triple cigarette lighter socket for other devices.
If I in the future need to connect some peripherals to a cigarette light outlet I have made this adapter. It could be when I'm out and time lapse shooting for example. Then it is enough with a regular small motorcycle or start battery.
Power supply connection on the EQ6-head is really poor. Have lose the count of how many times I lost the power supply to it. And after a power loss I have to initiate the equipment again which can take one hour. You can change the contact to someone else but the most secure connection is to don't have any contact at all. Have drilled a hole and pulled into a cable and soldered directly onto the circuit board. It felt wonderful!
The computer controls the EQ6-mount directly through software EQMOD so I do not need a hand-held terminal that maybe is malfunctioning. The adapter is a standard purchased from Hitecastro. Has worked well so far. The steering assembly with EQMOD, CdC, Cartes du Ciel also interact with the guide camera and APT to get the dithering (small movements of the telescope between exposures).
Canon 5D draws about 0.4 Amp under exposures and empties quickly it's own battery. Here is the battery dummy, I built one battery dummy of a discarded battery to connect 8 volts from a 12 volt converter. Inside the battery dummy I have put an electrolytic capacitor at 470 micro Farad that can take care of the instantaneous rush current when the mirror and the shutter is activated. The two wires are a USB for control and transmission of images, and a serial connection to take longer exposures than 30 seconds and feature mirror lock. I mostly use the control software APT that I'm very happy with.
My self-built 8 volt converter from 12 volts to the camera. First I had the electronics inside the battery dummy but it was not good because the camera was heated up by the power losses.
The computer is an ASUS EEE with dual core at 1.6 GHz and 4 GB of RAM. Computer hard disk can be replaced with an SSD to save some power. This computer will be remotely controlled with UltraVNC or similar programs. I do not therefore have to have long USB cable between the laptop and the equipment. USB to WiFi adapters usually supposed to not be so easy to get to work. The computer has five USB ports including 2 USB3 standard, so far I do not have an USB HUB, but maybe need it in the future when the focus motor and other accessories will come. I have neither the monitor or keyboard connected to the computer so it is important that you can trust that the remote control is reliable, has worked well so far. Shall later try to bypass the router and connect computers directly via WiFi, have never tried this before so it will be interesting to test.
Voltage converter to the PC, from 12 volts to 19 volts. Unfortunately have to have this one, the better would have been to run the computer directly to 12 volts which is how it working internally. But the battery voltage is too unstable to withstand computer requirements.
GPS unit, connected through USB. Good to sync the clock and get the right coordinates of location if you're traveling with the telescope. EQMOD can take the signal, it is not wise to let the GPS sync the PC clock. Better would have been to set the clock right away, I think that I now have a problem when the time difference becomes too large, typical a minute or two. What is not included here is the guide camera connection, previously held a webcam but it must be replaced by something better. Focus motor is no longer departed than thoughts in my head. Perhaps Hitecastros solution is good. Saw one who had it on a Star BBQ party in the other night. Battery monitoring would perhaps be handy. But actually, the one can not pick on a lot of things unnecessarily when they draw extra power. Heat Tapes for telescopes, I have never used it earlier but it is a must, the idea is to build an energy-efficient solution.Back to contents
2: Fuse box and fuses
Now, even the fuse terminal is in place:
This I found at the auto parts store. A robust thing that seems to be able to cope with some rough treatment, little clumsy maybe. I chosen knife fuses that are used in cars as it provides good contact with less risk of glitches. Should a fuse brake, and you forgot to bring spare fuses there are always someone in the car one can take.
Best to add, if used to charge while using the equipment then must charge current have separate fuse, otherwise unpleasant things could happen!
Now it's just a box missing, has been looking but have not found anyone suitable. Shall maybe build one myself if I can't find one in a proper size.Back to contents
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3: Box and charging
Here astro box taken a step further. Bought at a second market, a cooler box to mount the battery and the computer in. Good because the box's insulation will protect to some extent from outside cooling.
How the box will look during transport. The black plate is a mount for the cigarette lighter sockets. Chose to have it on the outside so I will not have arcs when connect and disconnecting connectors.
Here are the inside box equipment. Contains computer, voltage converters for computer, battery and fuse terminal. Later I have to secure the battery so it can not be sliding around inside the box. Here are also room for battery chargers and some accessories. A plastic shield have to be made across the battery terminals to isolate to not risk a shortcut.
GPS unit, here on the cover, a piece of metal glued to the lid so the GPS magnet holder can be attached.
Cigarette lighter sockets mounted on the outside as they are in operation. Will try to have as few accessories connected through this as possible. The contacts can be seen hanging out are the ones I will use.
How does it look when used. The large wiring harness to the right is for the camera,
the gray box is the voltage converter to the camera, cable to the left to control the assembly.
One must be careful when inclosing a battery like this, especially when charging it form explosive gas in the final stage. This battery has a valve that prevents fire / sparks outside penetrate the battery. But even this sealed battery leak small amount of this gas. This gas is hydrogen and it is a light gas that rises. The lid must therefore be off when charging. The charger is of a regulatory type which turns into maintenance charging when the battery is fully charged. The charger is connected to the cigarette lighter socket on the outside of the box to not get sparks near the battery.Back to contents
4: Overview computer and accessories
Did a supplement in the computer box the other night.
I have now had time to test drive the computer equipment in the field and everything has worked fine except for minor
communication problems with the Canon camera over USB connection.
Bought the USB cable of better quality and set the computers sleep function for USB to disabled.
Also for practical reasons I added a power switch that disconnects the power to a part of the connectors.
I did not have any switches from the beginning because it is a source of problems.
The power switch is located on the inside of the box to the left, looking for a plate angle to attach it to, it shall have a 20mm hole. Under the red plastic cover is the 45Amph car lead battery.
Summary of what is available in astro box today, this is the most equipment necessary for an evening of photo shooting:
In the computer is installed:
I remotely control this from a laptop. When I'm on the permanently place, I have a 24" externally monitor connected. And there is also a router. When I'm out on the field I I plan to connect the laptop directly to the equipment and does not use the built-in computer. In field mode the max distance is about 3 meter between the mount and laptop.Back to contents
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5: USB 5 volt external power
In my tests it have shown that use a USB without external power supply provides much trouble. In order to overcome it I have built myself a power supply for the USB hub. Started from a USB cigarette converter. Normally, you can usually take up to 2 Amp at 5 volts, the one I found in the drawer looks however very weak so have probably a much smaller maximum current, but enough for my needs.
In connection with this, I also disconnected the Focus driver so it does not take power from 5 volt USB. 5 volts gives to low torque of the motor. You can configure the controller as it takes power from the outside and can handle up to 8 Volts. It's the same voltage that I feed to the camera, i will modify the setup so that camera and motor focus share the same 8 voltage. A bit risky it is, step motors can provide some spikes on the voltage that in the worst case could destroy the camera. But I trust it enough to make an attempt.Back to contents
6: Motor focus power
Has now added an additional outlet on the existing 12 to 8 volt converter so that the focus motor can take the same power as the camera does.
Trying to keep down the number of components so it's very good that the voltage converter can be used for two devices. A word of caution, USB Focus as my focus drives is called, I am very pleased with, but one thing, the small switch to choose between internal or external power supply is very fragile. My broke when I was changed to the other state with a small screwdriver. Will you do something like this, disassemble the box so you can see properly how the switch should be moved. Now I made simply so that I removed the switch and soldered with a wire jumper instead.
(click on the image to get a full resolution photo in a new window)
Here is an overview, quite tangled apparently, the telescope is barely visible behind all the wires. But if everything works well without a lot of communications problems should I buy shorter USB cables A to B of 30 cm. Focus motor now had a completely different torque when connected to 8 volt supply, I can hardly hold it.
Even inside the battery box it has been cleared up. The battery under the red plastic cover. On top is the GPS receiver, normally sits on top of the lid. A mounting bracket for the power button is missing as well as a current and voltage meter, would rather have one that can be connected to the computer through USB, has not found anything useful yet. Between the telescope and computer I need two USB cables. One to control the Canon camera, the other to bulb control, EQ6 control, focus motor, guide camera. With the Canon camera I've had a lot of problems with the USB connection. Easily lose connections, now with separate cable the problem seems to be manageable. I guess newer cameras do not have this big problems.
I have also two power cables. One to the EQ6 mount. The second of the two voltage converters (Canon Camera, focus motor, USB hub), heat band.Back to contents
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7: Get rid of messy cables
Today arrived the special USB Type A to Type B cables of 25cm. I bought them at Cable Worldhttp://www.cableworld.se/
at the cost of 2 Euro each and 2 Euro in shipping.
How it looked before, quite messy but this was of course during the testing phase.
With the new short cables it gives a clean look. The cables are quite thin and smooth in room temperature. We'll see how it goes in the cold, the speed performance is probably pretty bad considering how thin they are. The test I have done has not revealed any problems yet in terms of the contact between the PC and the USB devices.Back to contents
8: Cleaning up installation
In an attempt to bring order to the clutter in astro box I bought at the auto parts store self-adhesive Velcro. Very easy to attach and handy when you need to take apart electronics boxes.
It looks a bit safer now, no cables become trapped, especially when motor focus leave from parking mode it is easy for any cable to rip off. There are now two USB cables and a power supply down over the mount and one to the computer. Later I bundle the cables when I have done all the tests.Back to contents
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9: First outdoor test
Got quite clear weather tonight. Out with the telescope on the balcony, it takes about 10 minutes. Then it takes one hour to calibrate the position and adjust the focus, but it goes faster and faster. The telescope needs one hour before it is thermally stabilized to the outside temperature, so can not get going so much faster if you do not allow the telescope to remain on the mount outside. M106 is at the east so that will be my evening's experimental object. But I can not expose more than 30 seconds at ISO800 and a f5 systems. More than that and I only have strong light pollution on the image.
Here how it looks at the astro server screen.
Device panel is up there so I can ensure that all USB devices remained at the same com port address. Imagine how good it would be if one could give an uniquely name to every device. Focus control has its own name, the other not. Guess it is permanently embedded in the driver's hardware. Do not in any case found a way to change the name of the other.
CdC (star map program also called Skychart) shows how the camera's field of view is, and make it easy to center the camera on the object. The small box corresponding the guide cameras field of view.
Here is how PHD2 (auto guide program) has locked onto a star (green cross) to guide. The guide camera is connected through an off-axis adapter and have relatively large field of view so it is quite easy to find a guide star. The flat field corrector is quite generous as it offers good brightness to the off-axis adapter corner. The main telescope in this setup has 680mm in focal length and that there is a full frame camera, which means that there are many bright stars available in the large field. If I have had an SCT with 2000mm focal length and a small CCD camera sensor it would have been much more difficult, I'm really impressed by you who handling such a system photographically. This star has magnitude 5 so it give the camera plenty of photons. I have tried down to magnitude 8 and it has gone well. The graph shows how the PHD2 gives a dither commando after each exposure. Unfortunately, it is quite easy to hit the the camera so that it is out of focus relative the main camera. Would be good with a motor focus on it too, but may be possible to solve with some sort of mechanical position locking of the off-axis adapter. The focus will of course only have to be done once otherwise when you change the system.
EQMOD control the EQ6 mount, 1 point calibration. Polar aligned quite carefully made earlier by operating align assisted by the guide camera and PHD2, within a few minutes of arc.
APT control camera focus and syncs with PHD2 so that dithering will be at the right time. APT is so advanced that it can handle multiple cameras with different exposure and sync for the best time efficiency. Maybe I can run two cameras in the future with two telescopes on the same mount, 680mm and 150mm. This applies of course to take advantage of the few clear nights I get in a year. Dithering movement is a bit too small for the pixel scale of this system, at least 5 seconds of arc would be good. But large movements also provide longer stabilization times so there is a bit of a compromise. The camera is controlled by a 3 second delay for the mirror to stop vibrate.
You have probably seen this exciting movie of what happens inside a DSLR when you expose? See especially how the mirror shakes!Canon 7D shake
It's very satisfying when you can do a test after all this work. Much remains, but the justification increases with little practicing on the sky objects from time to time.Back to contents
10: Replacing USB-Hub
One problem that I have had is that the USB-Hub is a little bit to big, it's barely that I can close the telescope box. And I can't place it close to the devices it connects to so I have to have longer cables than necessary.
I have now find this little used device.
It's the one to the left, a Deltaco UH-410 micro hub. That small devices normally don't have an external power inlet, this one had but no power adapter come with it. And anyway I don't have any use of a 230 volt adapter, I need a 12 volt to 5 volt adapter. I already have one, it's just that the connector was of the wrong size. I just soldered an extra connector to it with correct size.
I also tried to have it without the external power, but then as I already have experience from the data communication will fail.
Here the hub is mounted on the telescope with the USB cables connected. Much better, just have too test that it works also in the cold.Back to contents
11: USB-Hub and focus driver holder
Now it's time to do something about the messy impression of all cables.
A friend made this aluminum plate, the bolt that hold the dovetail to the tube rings also hold this. I have also rotated the focus unit towards the RA axis to get it more compact and in more balance. Up to the right is the guide telescope, I mounted that when I change to a 3" field flattener, maybe I can find parts to build an off-axis adapter once again.
On this plate I will mount the focus driver on front and on its backside the USB-Hub. I will draw them with Velcro.
Now it looks much better and I can have shorter USB cables.Back to contents