Gina

Very nice ? With my observatory I just got it to a state where it could be used and there it stayed! No paint on the inside though I did put rubber foam tiles on the floor - mainly in case of dropping things. It's had a fed upgrades but only to improve performance. Scope room not lined warm room insulated with polystyrene blocks and lined with 6mm mahogany plywood which I was going to varnish but never did.

I can get one like your photo from Amazon - £6.37 with delivery Tuesday. Might try that. CDA Tecnik Washing Machine Pressure Switch. Genuine Part Number 49579500

Currently printing the main casing - about a 4 hour print with about an hour to go. Clamping ring for dome designed and the base nearly finished. Wants a pipe connection for the pressure and maybe under-pressure sensor plus holes for the power connections. The two projections are for the water pipes, which should be a tight fit in the holes/tubes.

The water pipes and waterblock plus the heatsink will be at or slightly above ambient temperature and the enclosure air will be dried with silica gel sachets so this should not occur. The enclosure will also have a positive pressure of a couple of inches of water which will ensure that nothing enters through the plastic casing or seals. I usually give all electronics a spray of ACF50 anyway. I take your point though.

Been checking the NASA Images web site and found they are generally not copyright and I can show them in my talk.

A photo of the assembly so far with a partial print of the enclosure to confirm I can get the RPi and buck converter.

The obvious pressure gauge is a water manometer but that could introduce damp into the system. Been doing some reading and it seems the commonest liquids used in U tube manometers are water, oil and mercury. It only needs a very small increase in pressure above atmospheric, maybe an inch or two of water. I guess the amount of water vapour given off by a surface of a couple of mm diameter would be negligible compared with the volume of air in the enclosure and of the silica gel packs used to desiccate the air.

I have an idea for pressurising the enclosure which I'm going to try - a bellows for increasing pressure and a diaphragm for checking that pressure has been maintained. The diaphragm could operate a micro switch connected to the RPi to show pressure GOOD/BAD and be in the bottom of the enclosure so no wires need to go through the sealed vessel wall. I would have preferred a linear readout of pressure so that I could see if the pressure changed but that would involve much more complication. I guess if I pressurise through a tube, I could have a pressure dial in the observatory which I could check every so often.

Photo showing the camera support, waterblock and cooler for the RPi.

Yup!

Heatsink clamp. This holds a 40x40mm heatsink onto the waterblock (40mm x 40mm x 10mm copper). Fits between the fins and screws into the M4 holes in the camera body.

The focus ring turns quite easily, particularly at a radius of about 40mm. The focus quadrant should be a push fit on the focus ring as the hole is the same size as the earlier focussing setup which worked fine. I agree that a longer contact with the focus ring might be better or I might bring the motor further up though it's about the same as before. The stepper motor is the ubiquitous 28BYJ-48 with about 64:1 internal gearbox and the pinion directly drives the quadrant.

The ASC assembly less main enclosure, camera, cooling parts and RPi etc. Focus motor will be fitted under the camera support with the shaft projecting above and with a small 9t pinion on. This will engage with the focus quadrant gear attached to the focus ring of the lens. The gear ratio is 8:1.

This could be the finished design of the camera base and support. The focus stepper motor will be mounted on it too. It will fit inside the main enclosure and sit on the base, providing room for the RPi and buck converter plus the waterblock and heatsink attached to the Peltier TEC under the camera. There is a bracket to design and make for the latter.

Having said that, I do wonder whether applying positive pressure to the inside to the enclosure might have some benefit - not circulating air but just a positive pressure through a small tube with some way of checking the pressure to confirm no leaks. I'll give it some thought.

Thanks for your reply. No.1 is definitely possible and a good idea once I've built the new enclosure. I thought of No.2 but it's more complicated and the desiccant would want replacing pretty often. No.3 doesn't apply because disassembly is a requirement.

Been watching a science programme on BBC4 which mentioned the Challenger Shuttle accident and the cause, which turned out to be freezing cold weather affecting rubber O rings. Now I wonder if frost was the reason my ASC seals failed. Bathroom sealant is used at room temperature and not designed for large temperature range, particularly cold.

Camera housing base - thermally insulates the camera from the waterblock. Square hole takes the Peltier TEC.

Camera housing for thermal insulation. Shown in transparent blue.

The new design will use the 4" dome to give enough room for the dew heater resistors. With the outer casing being sealed there is no need to seal the camera housing - just provide thermal insulation.

Just realised I have the answer all along - I have water cooling and the waterblock can cool the RPi as well as the hot side of the TEC. At first I thought of an aluminium box for the RPi but then I realised that would stop the WiFi from working ? I can put the RPi below the camera and cool air from the waterblock can descend onto the RPi by convection. Now to redesign the enclosure...

Wearing my Heath-Robinson hat, the question of internal temperature could be overcome with a Peltier TEC and inside/outside heatsinks and fan(s). Cooling the internal air when too hot and warming it when too cool. ?

I'll try it - thanks. Ordered a tube. Also ordered some ceramic 5W resistors for the dew heater. I think the seal I made for the cables worked alright but I may put the RPi inside the casing and then I shall only need power, which is easy to seal. I was worried about high summer temperatures (ha ha) with the unit in full sunshine (if we get any) but I think an external shield spaced away from the main body should take care of some solar radiation. It would be open top and bottom so convection can take heat away. Of course, the dome would be in direct sunlight.

Just tested the top of the case that was sealed and found a leak. That part was not as well sealed as the other parts.

Hmm... that's what I thought and it was oozing out everywhere. I wondered if it was actually waterproof.