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Astro Projects

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All Sky Camera Mark 7

Gina

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This is my latest generation of all sky cameras and based on the ASI178MM followed by ASI185MC CMOS astro camera and a Fujinon fish-eye lens of 1.4mm focal length.  Although rated at f1.8, this lens lets a lot more light through than this would imply.  Image capture is provided by a Raspberry Pi 3 in conjunction with INDI software.  This is used with KStars/Ekos client software running on a Linux Mint desktop indoors.  Communication is via Wi-Fi.  The Mark 6 ASC has proved inadequate after being in use for some time. 

This blog will describe the problems of the Mark 6 and report my progress in developing this new version.

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Still to do :-

  1. Arrange place for Hall switch
  2. Add cable and connector to Hall switch device
  3. Make up dew heater with cable and connector and attach to lens
  4. Test that everything works
  5. Assemble everything

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Made up dew heater resistor string, connected wires (green & orange) to it and to the connector to plug into the HAT.  Also, inserted wires (black & red) from Peltier TEC into connector.  May be able to test the dew heater and camera cooler tomorrow.

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Soldered wires onto the Hall switch and tested it on a bench PSU.  With the magnet I plan to use, the switch operates at about 8mm when brought in from the front.  I plan for it to come in from the side for better accuracy.  The Hall switch is going on the inside of the top of the casing near the top and the magnet (3mm diameter x 5mm long) will go in a 3mm hole in the cover opposite the pivot.  Hall switch and wiring will be glued to the casing with hot melt glue.

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Connected dew heater and camera cooler to RPi and 13.8v power to buck converter.  RPi light on, checked voltages and all OK.  Ran Terminal and set the RPi running the INDI server then KStars/Ekos on the client machine and started up INDI control and connected the Astroberry Board driver.  Tested the dew heater and camera cooler controls and both worked fine :)  So I can now assembly things and run those parts of the system together with the imaging.

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Shut down, connected camera and started up again.  Here's an image indoors with exposure of 1ms and gain of 0 so the absolute minimum that INDI will go to though admittedly I haven't updated to the latest version of everything which I shall do later.  Offset needs adjusting but I now have grub screws for that.  The lens support now has an oval hole for the camera with M5 tapped holes and grub screws to adjust the offset.  I was glad to see that the ZWO camera driver works for the ASI185MC perfectly.

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Now trying the camera cooling.  Currently the camera is showing a temperature of 29.5°C with cooling off.

Later...  Camera temperature 17.1°C but the hot side is only onto the aluminium block without the aluminium tube to conduct heat away to the atmosphere.  It's just slightly warm to the touch whilst the camera body feels cold.  Cooling will be much better with the aluminium pipe.

Edited by Gina

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The USB cable with right-angle USB-B plug that goes into the camera has stopped working and I'm connected with a straight cable so can't fit the case.  So I've put the kit outside just hanging.  Exposure still 1ms and gain at 0.  The offset has moved again.

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Adjusted offset and focus but the field doesn't seem flat.  This could do with improving - if only I could think how!! :D  Making some progress in other directions though :)  ie.  Dew heater and camera cooler.  To show the benefit of the cooler I need a dark night - no moon!

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Clouds have gone!  10s exposure, gain 192, gamma 35.  Camera temperature 5°C with cooler on.  Dew heater ON.

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Edited by Gina
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Just had a brief light shower.  A few raindrops on the lens.  Dew heater is on so I'll see if the drops evaporate.

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Test abandoned - it's raining properly now so brought kit in as it isn't yet in it's waterproof case.  Camera case had ice on it.  Now drying everything out before running it again.

Edited by Gina

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No problem, running fine indoors.  I've ordered a USB cable with right-angle plug so will be able to put the works in it's outer casing and stop it getting wet.  Raindrops seem to dry off without leaving any trace on the lens.  May be different when there's Sahara dust in the atmosphere though!

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Been looking at the lens support very carefully and the lens is not tight in the tube in the Y plane.  I think the answer is to redesign the lens support with holes for grub screws in the part that holds the lens, just need to decide how many it will need.  Six would be the ultimate - three at the bottom and three at the top but I'm not quite sure how I would adjust them.  A first approximation would be to get the ceiling and walls all in focus in the living room.  Then maybe loosening two screws in line with the optical axis and adjusting the lens on a distant object for focus and re-tightening might get both focus and alignment correct.  Worth a try :D

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Meanwhile...  In trying to get the 3D printer to connect to USB, I noticed I was using a USB cable with right-angle plugs on both ends, about 3ft long, that would be ideal for my ASC.  Connected camera with it and it's fine.  (The USB problem wasn't the cable.)

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Before further messing about with the lens support (which I'm getting a bit fed up with anyway :D) I'm going to print a framework to hold the boards and fasten them to the camera part.  This is a test part to see how things fit.  Quicker and less strain on the old brain than carefully measuring up and doing proper CAD :D59fef9311a884_Frame01.png.a407c48381a805b7a17ac1e69269a646.png

 

Edited by Gina

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Redesign required.  Getting all the bits in the gap between camera, mounting block etc. is proving rather tricky.  It could have done with a bigger outer casing but I don't really want to redesign and reprint that.  OTOH maybe that would be easier - middle part would want redesigning and reprinting, top just reprinting since the present middle and upper parts are solvent welded together.  However, the top part could do with a slight redesign to accommodate the Hall switch better.

I think overall a redesign of the outer casing is indicated - there's nothing worse than trying to cram stuff into a tight space when it isn't really necessary, it doesn't matter how big the outer casing is (within reason).

Edited by Gina

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Here are a couple of photos of the bits and bobs attached to a frame and that to the camera body with a 3D printed clip.

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Tried the casing over the insides and, as I thought, it won't go.  In fact the main problem is the USB plug on the camera.  The rest might just go it with pretty much nothing to spare.  I shall need to adjust the case design to miss the plug as it's higher up than the part I increased in diameter.

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Redesigned the middle section and now printing the top section.  The showers seem to have stopped so I've put the rig (without casing) outside.  Here's an image.

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I was wrong about the showers having stopped and I've just been caught out - was watching the printing and not the camera display.  When I looked it was covered in raindrops so I've brought the kit back in - it's wet but still working.

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I think I'm satisfied that the new casing design will clear all the inside parts so I'm printing it.  This will take nearly three hours!  And 60m of filament - the 1Kg reels are around 400m or roughly £4.50 worth of this top quality filament.  I hope this print goes alright and everything fits - I don't want to print too many of these!!!

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