Automation Update - weather sensing

One of my goals in automating my observatory is to enable it to look at the weather and sky darkness conditions itself so that it can decide to make observations for me! I'm doing this with an eye on automated supernova hunting and comet/asteroid photometry. Prior to getting to that stage though, it needs to be able to check the weather to just safely park the scope and close the roof if it detects cloud/rain.

Cloud Sensor

After looking around on the Internet I found this and this which I found very intriguing. The Boltwood Cloud Sensors look great but seem very expensive for what they are (out of my budget anyway!) so I decided to have a go myself.

I used a Peltier thermoelectric cooler, purchased for a few £ on ebay, sandwiched between two small pieces of aluminium sheet. I used a small amount of thermal grease to make sure heat transfer would be as good as possible between the sheets and the cooler, which here works in reverse, i.e. the temp difference between the sky and the ground changes the potential difference generated by the Peltier device. The whole lot was held together with nylon bolts, mounted to the outside of the observatory and connected to a USB multimeter, purchased from Maplin for £20!

I used the provided software over several nights to calibrate the sensor - it was amazing to see the differences in the voltage generated by it changing as the cloud conditions changed.

I soon found though that rain did affect it - rain drops had the effect of cooling the top plate, but this usually changed the voltage much more than a normal clear night did, so is quite easy to spot. I did have a go with covering the sensor with cling film, but it didn't work for me unlike as mentioned in the second link above.

It was a fairly simple matter to talk to the multimeter in my program using serial comms.

Rain sensor

So my program now had a good idea about the cloud condtions, and could react to them, but I felt like I needed a rain sensor as a sort of failsafe.

I tried a KEMO rain sensor (purchased from Maplins) but I kept having problems with it giving false alarms. I have read others having issues with these so I decided to make my own, with a view to possibly buying something else later.

I purchased a small piece of gold stripboard from Maplin and used that to make a simple rain sensor. Each alternate strip is soldered together, with a power resistor mounted on the underside to help combat dew and dry off the sensor after the rain has stopped. The sensor was linked up to a simple transistor circuit controlling a relay, which I wired in to be read as an input by the K8055.

This sensor works well, though I do have to wipe the stripboard with wire wool about once a month to get rid of oxidisation. For this reason I will eventually upgrade to another commercial unit.

Sky Brightness Sensor

In addition to the Peltier-derived cloud sensor and the rain sensor, I wanted the observatory to be able to check that the sky was actually dark.

I used an old LDR that I've had since er.. school (! - that's >20 years!), made a mount for it using bolts and bit of waste water pipe. I also put a small piece of thin perspex over the top to protect it from the worst of the weather.

This was then mounted to the same pole as my electronic weather station.

I have found that the LDR is great for not just detecting day/night, but also clouds! As I live in a light-polluted area, the sky's light level at night changes depending on whether it's a clear dark night as opposed to cloudy. So I now factor this in to the decision-making as well as the Peltier cloud sensor.

Weather Station

I use a Maplin (that shop again!) USB "Professional" weather station along with Cumulus software, which re-generates a text file every minute which my program uses to check if there's been any rain in the last hour (which I class as "bad", in case of showers and to allow the cloud sensor to dry out a bit) and for high winds. I have to check the file is both present and current to ensure the data is up to date, so no old data is used.

Still lots to do - mostly programming, working on the logic for coordinating imaging while it's clear and dark. But I have a few updates pending still on this blog. Keep an eye on my Twitter account @cho_web too for updates on this project.

Automation Update - Power

Well a lot has happened since the last my last post in April on this project.

Having fitted sensors to the roof so that the software I'm writing can tell the status of the roof (open/closed/part open), I now needed to control the power to my mount and CCD camera.

I have built a simple relay box which controls the power to the mount and CCD. This is shown below. The relays are switched on/off by the K8055 and they turn on/off mains power to my two PSUs. Simple but effective!

I also have a webcam pointing at the PSUs so I can check for power lights if I ever need to.

Possible new lunar webcam

While still firmly stuck underneath a blanket of cloud and rain, I decided to modify a webcam that I had lying around for use as a possible lunar and planetary imaging camera.

The camera is a Logitech HD Webcam C270 capable of 1280x720 video, with USB2.0:

Modification was very simple.

First I removed the fascia:

I undid the three small screws that hold the front part of the case on and removed it. I then used a drill to increase the size of the hole in the front part of the case to accept a Mogg adaptor I had spare.

I put a little piece of black insulation tape over the LED on the camera board and unscrewed the supplied lens from the sensor housing.

I put the case front and fascia back on and then screwed the Mogg adaptor into the hole I made. I used a little superglue to secure it.

Et voilà!

The proof of course will be as they say in the pudding when I get chance to test the camera with my scope. It's likely that the video the camera produces will be compressed but I will experiment with the settings, and see what old faithful K3CCD Tools can produce with it.

Boundary layer fan mod

Something I've been wanting to have a go at for ages was installing a fan to help with cooling the primary mirror and especially a side mounted fan to hopefully eliminate the boundary layer of warm air that sits over the mirror that can affect seeing - see here. The normal way to minimise this effect is to just try to cool the mirror as close as possible to the ambient temperature. The problem with this though is that it does need to be very close indeed to the ambient temp which is difficult to achieve with fans blowing on the back of the mirror alone.

I did have a try using a Peltier cooler and fan combination but this still struggled to cool the mirror to ambient and I think would have needed a lot more engineering to go on around the mirror cell for it to be really effective. Anthony Wesley in Australia has done a lot of work on this using multiple fans and Peltier coolers, but his mirror cell (and the whole scope) is custom built and beyond my expertise and budget. My Orion Optics SPX250 already has a small cooling fan in the mirror cell, to which I have already added a baffle (made out of a rubbery Ikea placemat), to stop the air from just coming straight back out of the cell again and instead go to the edges of the mirror and up the tube. I also have an indoor/outdoor thermometer velcroed to the OTA to measure the ambient and mirror temps.

Baffle

Indoor/Outdoor Thermometer

A small, side-mounted fan can gently blow away the layer of warm air that sits above the mirror. Run at full speed and suitably filtered, it can also help with cooling the mirror itself.

So I set about removing the primary mirror and cell, and marking and cutting the necessary hole in the OTA.

I fitted the fan, oriented so that it blows air into the tube, and covered it with pc fan filter foam and made a grill to secure it out of an old oven-chip crisper. This was all secured by four small nuts and bolts. I added a 3.5mm sound jack (rescued from an old 56k modem) and wired it to the fan.

Fan inside

Fan outside

I have the fan plugged in to my 12V supply via a variable resistor so I can adjust the fan speed - full to help with the initial cooling, down to a gentle whisper across the surface of the mirror for observing.

12v Supply and speed control

The primary is back in the scope, it's all collimated again so I need some clear sky now to test it.

Roof Position Status

I've added two magnetic reed switches (of the type used in alarm systems) to the roof and wired them into two digital inputs on the K8055 unit. This has enabled my program to detect whether the roof is closed, fully open, or somewhere in between.

Observatory Automation

For the past few months I've been looking at ways to automate my observatory to make my deep sky imaging more frequent and more convenient, with a view to enabling supernova patrols and automated astrometry/photometry of asteroids.

I can already set up an imaging run but at the moment framing an object in the centre of the FOV and setting up autoguiding is all done manually. Once a night's imaging is complete (or I get too tired!) I park the scope, close the electrically operated roof and turn off power to the mount and the cameras. I tend to split time during imaging between watching progress while in the warm room and then maybe making a brew in the kitchen and watching progress via VNC on the laptop while in the lounge. Staying up all night doesn't make getting to work on time the following day easy! I can't leave it all running and go to bed for fear of the weather changing and it starting to rain all over the kit.

So after looking around on the Internet to see what's possible I decided to begin work on automating my own observatory, having three aims in mind:

1. To be able to leave an imaging run going and go to bed, safe in the knowledge that if it clouds over or starts to rain, the telescope will be automatically parked and the roof closed safely.

2. To be able to set a list of multiple imaging targets that will be automatically imaged during a night - including automatic framing through plate solving and automatic setup of autoguiding per target as required.

3. The final aim - to be able to provide the observatory with a list of imaging targets, which it will work through as weather conditions and hours of darkness permit. The observatory will sense when it is dark and when weather conditions are suitable. Alarms will be able to be set so that if anything "not good" happens then I will be alerted by phone. I will also be alerted when the list of targets has been fulfilled.

After reading various posts on the Internet, especially by http://photonjunkie.com/ I decided to use the Velleman K8055 PC interface module as the link between my observatory hardware and the observatory computer. It has eight digital outputs for driving relays etc, five digital inputs and two analogue inputs. It comes with a dll file which enables programming with various languages including visual basic 6, which I shall use.

First step was to connect the roof controls to the k8055. All I had to do was connect a relay to either side of the switch which I use to manually control opening/closing the roof.

I mounted the relays on veroboard and mounted the board alongside the K8055 in a plastic project box inside the warm room. I used the supplied vb6 demo software to establish that all was working and began writing my own program.

Next step - roof status detection.