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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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Hole made in main casing and lens cover motor housing glued on.  Next job is to design and print the arm that connects the lens cover to the motor shaft and there's the domed top for the cover which I shall print in black to provide for taking dark frames.  I've already printed the motor cover plate but won't put that on until I have completed tests.

5a402f484efe7_ASCinCasingwithLensCover02.thumb.png.e8d4de64f08a2ebd66289e520ede13be.png5a402f4c8549f_ASCinCasingwithLensCover01.thumb.png.e71a88936fee2e274b6ed20495a9400a.png

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I think I may have to redesign the lens cover motor housing top part as I suspect the lens cover might not go round far enough - have to see.  At least it's easy enough to redesign and reprint.

5a4040c84b72e_Cross-SectionDiagram05.png.710301e639daab818444c7f2a4fb259b.png5a4040c8b309b_Cross-SectionDiagram04.png.f45b09a06317a36dead749c45d39db88.png

Edited by Gina

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Gina, what is the gap between the neck and the cap sides? There does not appear to be enough of a flair on the cap to allow it swing off, or is that just the way it looks on the drawing?

Ed

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Aarrgghh...  Thank you, I think you're right - I checked it with the earlier design but forgot for this one so it looks like "back to the drawing board" or in this case SketchUp...  Probably a longer arm is the answer but I'm about to test in in reality.

5a40d7f04278e_Cross-SectionDiagram08.png.f8cc8bf8280d1f4e70737f19ef18ef6f.png

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Arm glued onto cover and waiting for the glue to dry.  I think there is more room between the cover and the lens tube that there appears in the diagram but I'll know soon.

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The lens cover cleared the tube alright but (as I thought) it doesn't rotate far enough to give a full sky view.

5a40e86a9c4f8_LensCoverOperation02.thumb.png.8dbf7e746f3341ab8b7a573f46c8be7a.png5a40e86ea419f_LensCoverOperation01.thumb.png.505a1c31af3f81a5a3d2bfcb297e09f5.png

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New top cover motor housing designed and printed ditto arm for cover.  Arm glued onto cover.  The cover could do with going down a bit further, maybe move the arm attachment point a bit. 

5a411d1ef17de_CoverMotorCasingTop04.png.669b6caa51d85fb6ada5363a2a88aab5.png5a4123d3e4dda_LensCoverOperation03.thumb.png.b02fdd3c8685f6550b86e937f34d0fb2.png

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That's the drive for the lens cover sorted out and the next thing is to determine how the position will be sensed.  I'm thinking the most reliable system would be to sense the positions of both closed and fully open and best sensors would be Hall switches.  One idea would be to have a magnet embedded in the arm and strategically placed Hall sensors in the casing.  The INDI code can read the Hall switches and the stepper motor stepped in the appropriate direction until the associated Hall switch is activated.  A failure condition would exist if the number of pulses sent to the motor exceeded a certain number.

Regarding connections to the RPi, I have already assigned GPIO5 for a Hall device as it has internal pull-up.  GPIO6 is currently assigned to the dew heater but the dew heater could be run from GPIO12 and free up GPIO6 which has pull-up.

Edited by Gina

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Hall sensors connected to a ribbon cable. 

Hall Sensor wires :-

  1. Brown - Open sensor Gnd
  2. Red - Open sensor +5v
  3. Orange - Open Sensor Signal
  4. Yellow - Closed Sensor +5v
  5. Green - Closed Sensor Gnd
  6. Blue - Closed Sensor Signal

Colour code for ribbon cable :-

  1. Brown - Gnd
  2. Red - +5v
  3. Orange - Open Sensor
  4. Yellow - Closed Sensor

5a4243dbdb593_MotorHallSensorWiring01.thumb.png.4cf458c5f058d89e60a9fdb1bca26ffd.png

Edited by Gina

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Now printing a new arm design incorporating a hole for the Neodymium magnet - 3mm diameter x 4mm long which will operate the Hall sensor switches.

5a424bbbb546b_Arm01.png.59e28a72659dbb278d909b5bf59b685c.png

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Magnet pushed into hole, arm pushed onto motor shaft, arm end filed to fit lens cover and glued on.  How just waiting for the glue to dry then I'll check the open position.  Slowly plodding on :D

5a425365a292c_LensCoverOperation06.thumb.png.5667bb3088571c31720b7172c62deb8b.png

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Open position.  Lens cover is slightly above level with the lens but it will be to the north where there are trees and rising ground and also where I can't quite get 180 degrees anyway.  So adequate :)

5a425a6dc2010_LensCoverOperation07.thumb.png.feacce1946298f09c90af01729e28de1.png

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Testing Hall sensors. 

The open sensor orange wire, not there yet.
5a4291c255a21_TestingHallSensors02.thumb.png.fd05e3336c1200e9b710603d72f4aace.png

Open state detected.
5a4291c71be7c_TestingHallSensors01.thumb.png.bc501d6991896d035a6d6d786adff49e.png

The  closed sensor yellow wire, towards the closed position but not there yet.5a4291be28f9f_TestingHallSensors03.thumb.png.b2f2b8f6df5d8b49eb5b790bfa31db23.png

Close state detected.
5a4291ba3f489_TestingHallSensors04.thumb.png.3371ae578ad3e483ad3a70a99ca2e508.png

Edited by Gina

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I have a problem!  My Antex XS25 soldering iron has packed up :(  Lasted just under 18 months - my previous one lasted many years!  Nothing seems to be as good as it used to be :(  Ordered a replacement from Amazon Prime but not expected to arrive until Thursday!  Blummin' typical packing up in a holiday period!!!  Maybe I'll order a replacement element as well and put it in my present iron, then I shall have a spare iron.  I guess the "insurance" price of £13 is probably worth it.  I think I have a cheapo clumsy spare iron somewhere.  Probably in one of the 10,000 boxes of bits I have all around the place!!

EDIT - OH!!  Found Amazon are out of stock of Antex replacement elements when I went to order - said two left on the main page, guess there's been a run on them!!!! :( 

Edited by Gina

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I think there are some things I can do without a soldering iron but not sure if I can get it working without.  There's some clear sky forecast for tomorrow night and I was hoping to test it using this very rare occurrence.  I need to provide connections for the Hall sensors on the RPi HAT so won't be able to test the remote opening and closing of the lens cover. 

A bit later... Checked what still needs doing and there's the buck converter to solder to and connect to the RPi so unless I can find and make use of that other soldering iron, I shan't be testing tomorrow evening!

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Found my spare soldering iron and it heats up :)  Probably won't go into town tomorrow - I expect it'll be very busy and there's snow forecast for the early hours tomorrow :eek:

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Found the arm wasn't attached to lens cover correctly so broke the joint and re-glued it.  Seems fine now and hoping to test the remote operation later today when I've connected up the electrics.

5a436c13337bf_LensCoverOperation08.thumb.png.cc7ff097743a05334d66313f03975f51.png5a436c0d5384b_LensCoverOperation09.thumb.png.39f3ed0ecf84cff22930dcd3d04fa57a.png

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