Easy Allsky mounting for Raspberry Pi and camera

After a big aurora display in May 2024, easily visible from my light-polluted suburban location, I decided I wanted to implement an all-sky camera. A very popular implementation is that originally written by Thomas Jacquin (https://github.com/AllskyTeam/allsky), which works on the Raspberry Pi and has support for various cameras. I wanted my camera to be largely maintenance-free, whilst still being easy to set up and maintain when needed.

I based my mounting hardware design on the bayonet principle. A 95 mm hole is drilled in an IP65 enclosure (I used 230 x 180 x 88 mm3 to give plenty of room) to accommodate the camera and a bayonet ‘socket’ is glued on the inside around the hole (orientation is important but hopefully obvious). The RPi and the camera are fixed to the bayonet ‘plug’ using small self-tapping screws. The camera is fitted first, along with its ribbon cable (which passes through a slot in the bayonet plug. Then the RPi is fitted on top to make a single unit. The ribbon cable is given a twist and plugged into the RPi. This makes it very easy to install and remove the camera for maintenance. A 100mm clear dome is glued with silicone sealant to the outside of the box, covering the hole and the camera. I used an inexpensive but very good quality dome from a well-known Chinese website. The knurled part of the HQ lens holder is easily accessible on the other side of the bayonet plug for focussing. A Module 3 wide angle camera also works fine. I have two cameras running: the HQ camera is fitted with a fish-eye lens so gives a true all-sky view, whereas the other is a wide angle Module 3 and points at the northern horizon. The Module 3 cameras don't have a focussing ring, but I found I needed to black out the copper-coloured features on the camera surround as they reflected on the inside of the dome under just about any lighting conditions; a black marker pen was fine for doing this.

A novel feature of this design is the dew control. Normally people install a ring of resistors around the camera, which get warm and (hopefully) suppress dew formation inside the dome. I didn't want the aggravation of doing this. An RPi 4 will dissipate up to 15 W when working (which is significant, in a small volume) and I decided to make use of this waste heat for dew control. This was achieved by installing a small 5015 blower fan which draws air across the RPi PCB and forces it into the dome. The air can then escape through a series of vent holes around the bayonet plug. Apart from a cable gland there are no vents in the box, so no insects or moisture can get in. The fan ensures that the warm air is evenly distributed throughout the entire enclosure and dome. This actually works extremely well - I have had two units running outside for over a year in all weathers and never had a problem with dew. It's important to seal the enclosure in an environment with low humidity (e.g. outside on a cold, dry winter's day).

I drive the all-sky camera with a 12 V, 3 A DC supply at the end of about 15 m of twin-core speaker wire. This passes through a sealed cable gland and splits two ways. One side drives an encapsulated 12 V to 5 V DC-DC converter to deliver 5 V, 3 A to the RPi via the GPIO. The other side feeds a low-cost generic LM2596S buck converter PCB which drives the fan. The buck converter is set to have the fan running as slow as practically possible. This reduces noise and vibration and probably helps with fan life. Note that if the fan starts squeaking, it's possible to lift the label up from the centre and drop some light oil onto the spindle, which should fix it.

The fan is fixed to the body using a single M4 screw, which self-taps into the bayonet plug, so it shouldn't be over-tightened. The PCB is fixed to the opposite corner of the fan using one of the holes in the corner (which needs enlarging to accommodate an M3 screw). Both parts could be glued if preferred (e.g. with silicone sealant). 

It's clear from the photos that I made ample use of Dupont connectors and soldering / heat-shrink tube to wire up the power supply and fan. Duponts are particularly useful to allow the RPi / camera to be removed completely from the enclosure during maintenance. 

Note that a small lump of blu-tak was used to cover the RPi's LED, which would otherwise bathe everything in a red glow during long night-time exposures.

I used black PETG for all the files as it's tough, resilient and doesn't soften unless it gets really hot.