Mountings and Controls For Widefield Imaging Rig

[Gina]

Thick clouds are staying over to the SW but high thin cloud is coming in from the east and there is also some to the west.

[Gina]

I'm not going to "bust a gut" trying to get the focus system finished in the hope of some clear sky tonight.  I've learnt long since that rushing things doesn't help and usually ends in disaster.

[Gina]

Looks quite good but there is still thin high cloud.

[Gina]

The cloud is really coming in now.  I increased the exposure to 20s and could make out several DSOs before the clouds came in.  M42 is generally easily visible and when I went over to Cassiopeia and moved the image over to where the Heart and Soul Nebulae should be, there they were.  Rather faint but quite recognisable.  Now the cloud has covered them.

[Gina]

Cloud nearly covered the sky now.

[Gina]

And now it's all over.

[Gina]

Solid cloud I meant...

Anyway, still plodding on with the construction of the electronics for my widefield rig.

Adopted Tekkydave's idea of soldering wires onto the underside of the RPi on the test points for the incoming power rather than having a very awkward plug sticking out the side.  But I have a different version and the PPs are numbered differently so I had to check continuity from the power input plug.  Here are photos of the board before and after adding the power wires.

[Gina]

This photo shows the wiring from the RPi GPIO pins to the sockets for the A4988 stepper driver module for focussing.  Some of the interconnections between the two driver modules such as power and ground and the +3.3v power from the RPi to the stepper drivers (white wire) can also be seen.  The ground connection for the stepper drivers is run directly from the main power ground (black wires).

[Gina]

The second stepper driver (left hand one in the photo above) drives the NEMA17 stepper motor that drives the rotation system.  This will be controlled by an Arduino Nano which in turn will receive 4 data bits from the RPi GPIO pins driven by the Astroberry Board INDI driver.  Later I might write my own INDI driver to control the rotation directly without the Nano.  As an interim measure I'm hoping to modify the Astroberry Board driver to provide a more appropriate GUI.

Arduinos work off +5v but don't actually have a +5v power input except for the USB which I won't be using once the sketch is installed.  I don't really want to wire onto the board so I'll be using the +Vin pin which requires between 6v and 20v though best run from around 9v.  I'm not asking the Nano to provide power output so I guess the 13.8v main supply will do.  It won't be doing any fast data processing either so I think the internal voltage regulator should be fine fed from 13.8v.

[Gina]

Been continuing the circuit board wiring but in a break for coffee I've been thinking about the rotation control, as that is the next thing having wired up the focus control.  The Astroberry Focuser driver has provision for setting several specific focus positions (think it's three) so I'm wondering if I could modify the driver to suit the rotation. 

Since there is already one Astroberry Focuser driver in use, I would have to rename the new one so that that the client would know which is which and avoid a clash with two with the same ID.  I would also need to change the GPIO pin allocation, of course, but that's easy.  I'm wondering whether this might be no more difficult than writing the sketch for the Arduino.  OTOH there's the Home position to consider.  Some research needed...

Maybe the best approach for the moment might be to finish off the wiring so that I can test the focus operation.  The rotation control is not essential for imaging - I can set it by hand - the focussing and power is essential.

[Gina]

Checked the Astroberry Focuser - yes, 3 presets - mutually exclusive (of course).  So as it stands it would give me 3 positions - nowhere near enough.  I think adding more would be just duplicating parts of the code to add more controls but this would complicate the GUI too much.  Rather than having three presets that can be altered from the GUI, it would be more sensible to have a bigger number of fixed angles.  Or alternatively, a text box into where the angle in degrees can be set.

Actually, I've looked at the code for the focuser and there is far more in there than I would need for the rotation angle eg. it has variable speed - I don't think this would be necessary, all it needs is to rotate relatively slowly from one position to another.  In fact the only thing my rotator has in common with a focuser is that it controls a stepper motor.  From the user aspect, it's more like a filter wheel (for say 8 fixed positions).  OTOH the idea of setting the angle in degrees would be the ideal IMO.

What I think I need to do is look through the code for several drivers and then combine appropriate parts from each.  Since all the code needed is in just two places - the .h and .cpp files this should not be all that difficult.  I'm used to C++ programming, having modified the Arduino libraries and, of course, the Arduino sketches.  Simply modifying one drive is not going to hack it.  Or is it...

[Gina]

Still thinking...  the focuser has a lot of the functionality I require - text boxes to enter numbers albeit focus ticks rather than degrees but if I find the relationship between rotation angle and focus ticks I could add code to provide the appropriate multiplier or divider.  It might be useful to have three presets - 0, 90, and a variable no. of degrees. 

Alternatively, since there is already a main focus variable (two in fact - absolute and relative - I could remove the relative controls) and three presets, I could make the presets really presets that I could set up for particular targets.  That would allow me to change targets without having to set the angle in degrees.  Much food for thought

[Gina]

Here's a couple of screenshots of the Astroberry Focuser GUI unmodified.  Controls could be removed for Direction and Relative Position and the label "Ticks" changed to "Degrees".

[Gina]

I think I've finished the wiring for the focuser.  Now to test it...

[Gina]

It works  

Oh no it doesn't - only goes in one direction   Should be able to sort that out...

[Gina]

Examined the board and connections and all correct so I've swapped the stepper driver for a new one.

Result - same - so not a bad driver.  Hmmm...

[Gina]

This is odd.  DIR connected to 0v rotation clockwise, connected to +3.3v no rotation.  I think I must be getting confused as that makes no sense at all.

[Gina]

I'm testing the brown wire which is connected to the DIR pin on the driver.  I think the images below prove this.  I have checked with my DMM that the 0v or +3.3v are reaching the driver pin.  I have also checked that the DIR pin socket has no connection to anything else when the driver and brown wire are unplugged

[Gina]

Double and triple checked everything again and found nothing - I'm stumped!!   If anyone has any suggestions I'll be very grateful

[Gina]

I've tried changing the stepper driver now I suppose I could try changing the RPi but I can't see it being that.  But then I can't see what it could be so I'm chasing shadows!!

On second thoughts I think I'll leave it for today and maybe something will occur to me overnight or perhaps someone will be able to suggest something.

[hughgilhespie]

Hi Gina,

Might be worth seeing if the direction changes if you use a 5v supply to the DIR pin. The Allegro A4988 data sheet says the logic voltage range is 3.0 to 5.5 volts. Maybe you are too close to 3 volts?

HTH, Hugh

[Gina]

Thank you Hugh

Yes, I can try that but a copy of this circuit is working for my scope rig.  In both cases I'm running the logic power on the A4988 from +3.3v in both cases.  If I connect the DIR to +5v I'll have to run the driver off +5v logic power.

[Gina]

Nothing has emerged from the back of my brain overnight but I am wondering if the longer connections from RPi to driver could be the problem.  I have a HAT with driver on it that I'm thinking of trying on the RPi.  This is similar to the HAT I'm using for the working scope rig.  I realise now that it would have been better to have the driver for focussing nearest to the RPi - might change it.

[Gina]

Regarding an INDI driver for the rotator...  This will require a lot more reading and research.  I won't continue to post about it in here as this thread is about the mounting and rotation hardware.  I already have a thread about INDI drivers so I'll post in there.

[tekkydave]

Have you tried running the logic ground directly from the RPi?