Allsky camera

Allsky camera - Version 2

Our current allsky camera

Main features:

IP66
Raspberry Pi 3B+
Arducam IMX462
CCTV dome
Dew heater

Why an allsky camera?

Do you know how it feels? Your astrophography session is all programmed, no moon, no rain, no clouds... let's now press "Start".

But a little voice tells you to open the window and check the sky one more time before you start opening the observatory and... damned. Hair-like cirrus clouds cover the sky with their delicate silky sheen.

Let's try again tomorrow.

No moon, no rain, no clouds. Last check through the window. It's confirmed: no clouds at all.

The session starts well and the day after, you realize that half of the frames are unusable. The faint cirrus clouds were back, but later. Post-processing is still possible, but how to know which pictures are correct, and which one are blurred?

Hmmm... there might be a reason why most of the observatories have an allsky camera but...

Why a DIY camera?

...but you just had a look on your favorite astronomy online shop and that tiny camera costs almost 1000 Eur!

You look at your soldering iron with determined eye, sure about you ability to do it for half of this price and guess what: after 5 minutes spent on the internet, you realize you can do it for 5 times cheaper.

Requirements

Because yes, all good things in life have to start with a list of requirements. What do we expect from our camera?

Withstand the weather (Rain, heat, cold, humidity, etc.)
Avoid dew
See a large portion of the sky
See the clouds
Be easy to maintain
Wireless

Ideally, it should also be compact, and look not-too-bad.

But before you heat up the soldering iron, let's have a good start.

Reuse when you can!

Before starting a new project, we always ask ourselves the sames questions:

Is there any open source projects for hardware and software?
What are the usual issues encountered by the astro community?

A short internet search shows that most DIY cameras are based on the excellent project made by Thomas Jacquin. The software is available in open source, based on a Raspberry Pi and either ZWO cameras, or Raspberry Pi cameras.

The main issue seems to be related to dust, due and heat. Here, many different solutions are available and each DIY project proposes another solution, depending on the environment and budget.

Since the weather can be very humid in Austria, a dew heater is probably a good option.

The right place

I know. you can't resist the call of the soldering iron but before you proceed, think about where to place each component and where the cables will be. Don't hesitate to spend half an hour trying different positions until you find the right compromise for optimizing the cable length, compactness and ease of maintenance.

Once you are satisfied, you can screw or glue the components. Personally, I prefer the glue for two main reasons: it's easy to remove, and every hole is a potential water leak.

The right components

Avoiding dew on the dome is easy in theory: the cold surface has to be warmed up. But wait, since all electronic components have a certain heat dissipation, why not using it for warming up the dome?

On the paper it works: All electronic components including the Raspberry Pi have a heat dissipation of approximately 3W. Nevertheless, it could be a little too less to melt the ice on the dome. Therefore, a few additional watts could help, ideally based on a 12V DC supply.

Part list:

Plastic enclosure (160x160x90mm IP68)
Dome (JMX Acryl for CCTV cameras)
Raspberry Pi 3B+ 1GB (with Wifi)
Arducam IMX462 (ultra low light camera used in the ZWO ASI 462)
12V power supply (on DIN rail)
DC/DC converter 12V/5V
DC Relay
5x 5,6 Ohm 2W resistances
Waterproof push button switch
Temperature and humidity sensor (SHT31-D)
3-pole connector (IP68, Aviation type)
Cable terminals (Flintronic)
Nylon M2 assortment kit (Litorange)
Dupont connectors (and a lot of patience)
30g desiccant

The right cabling

Let's be honest, we all did it one day: There are only green and blue wires left in the box, and not enough terminals.

"No matter, I'll fix it later"

And we both know: "No you won't" :-)

My piece of advice: just order enough wires of at least 10 different colors and from different diameters, plenty of terminals (Pin, ring, fork, snaps, Dupont, etc.) and good tools. I really mean it: Good tools! You won't regret the 50 euros you have just spent.

Scalability and maintenance-friendliness

An electric component needs to be replaced? A new feature needs to be added? Sooner or later, the box will be opened again. What annoys today will annoy us even more in 6 months. My lessons learnt so far:

Glue instead of screw, whenever it is possible
All screw heads facing upwards (I know it sounds obvious but... :-)
Lots of terminals, especially for 12V, 5V, GND, SDA, SCL
Connectors or clamps for each removable part (here: the camera mounting plate for example)
Standard components, easy to replace

In this project, I decided not to wire the dew heater to a Raspberry Pi GPIO first. Instead it is connected to a simple push, in order to perform some tests first, and decide later if a higher power is needed. The resistances are now connected to the 5V output, resulting into a heating power of 1W only. If later on, an increase of power is needed, I just need to build an adjustable DC/DC converter and select the right voltage for the right power (Power = Voltage² / Resistance).

I also measured that most of the heat goes through the plastic enclosure and not through the dome. This is not ideal, since we want the heat to warm up the dome first. If dew problems happen, I may install a thermal insulation later.

Airtight seal or air circulation?

Our allsky camera is supposed to be IP66, maybe even IP67. This means that no water is supposed to go inside even during a heavy rain.

"Yes but it will heat up inevitably!"

It is right, but I use this heat as a dew heater, together with 30g of desiccant. The humidity inside is stable (around 60%) and the inner temperature usually 7 or 8°C above the due point.

On-site test

No matter how well you plan, things are different from the moment it is located outside. It was hard to accept at the beginning, but a few prototypes are usually required and a modification is not a sign of failure. The new camera must now face the harshest conditions: Sun, rain, ice, wind, humidity, pollen, bugs, birds...

Old versions

Allsky Camera - Version 1

The first version was a prototype, made with a 5V DC supply only, without dew heater, and with an old Raspberry Pi camera version 1 which couldn't exceed 970ms of exposure time. This camera had also small pixels and high resolution, resulting into a poor low-light capability and large files.

Quick and dirty design, but this prototype fulfilled its mission: to identify what is important and is useless.

Allsky camera - Version 0

Because you have to start with something, somehow...

For those who think this project is crap and could be 100 times better, I can prove to you that it can also be 100 times worse. Before the prototype, the demonstrator:

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