The summer holidays are a good time to undertake new astronomy-related projects that are adapted to the circumstances of being on the road. In this case, and taking into account that I was going to be in a different environment from my observatory and in the meteor shower season, I decided to set up a portable AllSky camera.
The design of the portable AllSky camera allows you to choose the location where the images will be taken, and for example, as I intend to do this summer, to get a video or a Star Trail that captures a meteor shower. My observatory is in an urban environment and portability provides the advantage of being able to choose dark skies for the shots.
Making an AllSky camera portable basically consists of powering the camera with a battery. This is the summary, but there are a few things to keep in mind that complicate the design a bit. Here I list the ones that seem to me to be most relevant.
Waterproofing of the system
In the design I have not aimed for a system that is completely waterproof and can be left outdoors for days or months, but that is sufficiently waterproof to be able to leave it outdoors for a night and that the battery and electronics are protected.
For this I have chosen a plastic box (used in electrical installations) with IP56 protection thanks to a rubber gasket that seals the lid with the rest of the box. The box itself is sealed, but some machining has to be done and the result is somewhat less watertight.
In particular the following machining needs to be done:
- Drill hole in the lid for the camera bracket.
- Rectangular opening in the lid for the voltage meter.
- Lateral openings for cable outlet.
All these machining can be sealed internally to maintain the original watertightness of the box, but I have not considered it necessary for a use of the equipment that is not completely unattended, so that normally it will not be left capturing rain for days and days, but if one night it suddenly rains without being foreseen, nothing will happen to the equipment.
System power supply
The first aspect to consider is the need for 5V power. You can use a battery that offers 5V output but I don't think it is the most useful. You have to tend towards the standard and practical, and that is a 12V battery, which is easy to find and cheaper.
For this project I have used the same lithium battery that I use for the telescope when I need to power the mount in the field; this way I give it a double use. It's a LiFePO4 golf car battery with a capacity of 20Ah and a nominal voltage of 12.8V. It's reasonably light and small sized for this project.
To get the 5V needed for the system, it is necessary to use a DC/DC converter to convert the 12V to 5V. It is important that it is capable of delivering at least 3A, which we will need to power the electronics and the camera. In this case I have used the JZK A2 DC/DC converter with USB output. The USB output is very practical because it allows you to power the electronics without connectors. This kit can be found on Amazon for 8.99€ today:
Battery level
If we are going to capture an evening's images, it is important to ensure that we have sufficient battery level.
In the design I have provided that there is an on/off switch for the system, and that when it is on, the battery level is shown on a backlit display. This is achieved with this battery meter, which currently costs €12.98 on Amazon:
Wiring diagram
The electrical schematic of the system is shown below:
Camera control
To control the camera we have chosen to implement the project "A Raspberry Pi operated Wireless Allsky Camera" developed by Thomas Jacquin and very well documented in these links:
The requirements for the system are:
- A camera (Raspberry Pi HQ or ZWO ASI)
- A Raspberry Pi (2, 3, 4 or Zero)
I have used an ASI224MC camera and a Raspberry Pi 4.
In the documentation provided there is a good description of the steps to be taken for the installation and the subsequent configuration and use.
Construction details
An electrical junction box has been used which has been machined on the side with the cable outlet: a cable gland for the USB 3.0 cable that goes to the camera and a male and female ethernet cable (so that communication with the system can be done by WIFI as well as by ethernet).
The lid of the box has been machined to fit a bracket to which the camera is attached. The bracket has been purchased from Amazon at a price, as of today, of 15.99€:
As the head is attached to a plastic cover, a metal plate has been placed on the inside of the cover to give the whole thing consistency.
The idea of attaching a ball head is to be able to orientate the camera in those places where pointing the zenith is not the best option, or for example if you want to make a Star Trail and the Polar is in the center of the image or in the position you want.
Results
The portable AllSky works very well and is very easy to use: place it in the desired location and turn it on; the next day you can download the images, both individual images and a video of the whole night and a star trail.
Before taking the equipment to a dark area to take good shots, I tested it in an urban environment and below is an example of a star trail:
By the way, can anyone tell me what that trace in the image could be? In the video you can see that it is an object that appears in the sky around 4h local time (Madrid, Spain) and it moves slowly so that the recording captures several hours of its movement.