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MUP Astro CAT

The MUP Astro CAT is an auto GPIO configuring add-on board for the Raspberry PI 3 which provides additional hardware interfaces to communicate and control a Meade Autostar, Moonlite focuser and temperature sensors.

MUP Astro CAT

This repository contains the hardware project files needed to build the MUP Astro CAT. Firmware and the INDI driver is available in a separte repo:

https://bitbucket/org/BWGaryP/mup-astro-cat/

Please refer to the additional documentation in the docs/ directory for information on port pinouts for cables and hardware testing notes.

CAT refers to the Schmidt-Cassagrain telescope (CAT for short) this board will be attached to. After naming it CAT I considered the recursive "CAP" which would stand for "CAP Attached on Pi" since this project doesn't quite meet the "Hat" spec, a cap is not a hat! but that means renaming things so CAT it is.

Directories

  • control_cat - Kicad project incl schematic/pcb layout for the MUP Astro Cat. (CERN)
  • docs - Documentation and 3rd party datasheets
  • gerber - Exported gerber files for re-ordering PCBs

Intended Purpose

Use a raspberry pi and additional interface board to control the following devices:

  • SXVR-H9
  • LodeStar
  • Filter Wheel
  • LX90 Handset
  • Moonlite Focuser
  • Illuminated Reticle (v2?)
  • Temp Sensor

The SXVR-H9, LodeStar (excl ST4 guide port) and Filter Wheel simply connect as USB devices to the Pi.

The LX90 Handset uses a RS232 connection via RJ22 to the PI.

Moonlite focuser controlled via GPIO to a unipolar stepper motor controller that will handle signal timing. Ensures any jitter/pauses from pi due to non realtime OS won't impact motor control.

ST4 port from APM is not implemented, it might be added in a future revision via i2c bus however as the LX90 supports pulse commands over serial, it may not be needed.

Library Setup

In addition to the libraries, modules and models that ship with Kicad, this project also uses the MUP Kicad Library for additional parts and an optional 3rd party 3D model library.

Eeschema

If you receive a "The following libraries were not found:" message when opening the schematic then you do not have the MUPS Kicad library available. Kicad will use a cached copy of the library so this step is optional, but if you wish to make changes you should clone the repo:

https://bitbucket.org/BWGaryP/mup-kicad-library

and add its location "Preferences/Component Libraries" as a user defined search path in the "parts library editor". Then close and re-open Eeschema and all the schematic symbols should now be found.

Footprints

The above repo also contains footprint files for PCBNew in the modules/ directory and 3d models (where applicable). PCBNew will need each modules/*.pretty directory adding to the global library, or if you prefer, the project specific libraries.

To do so, open PCBNew, "Preferences/Footprints Libraries Manager", then "Append with Wizard" and select each ".pretty" directory and click Next, then select whether to add the footprint to the global or project library.

Note: Some footprints are unchanged Kicad footprints that have only been saved to the MUPS library in order to associate a 3d model with the footprint. If the official Kicad library ever adds the missing models, the parts will likely be removed from this repo.

3d Models

Some parts include a reference to models from the GPL'd 3d library by "kcswalter". These are optional models and not included in the MUPS Kicad library.

If you checkout the walter repo from

git://smisioto.eu/kicad_libs.git

You can have Kicad use these models during 3d preview mode by adding a new env variable in PCBNew "Preferences/Configure Paths" called WALTER_KI3DMOD and with the path set to the <walter repo checkout path>/modules/packages3d/ directory.

Any footprints in the MUPS library that has the 3d model path prefixed with {WALTER_KI3DMOD}/walter/ will then use the appropriate 3D model. The same will apply to {MUPS_KI3DMOD}/mups/ although at this time I've yet to create any custom 3D models and find it unlikely I will

Gerber Export

For Ordering PCBs from dirtypcbs.com

For "plotting":-

  • "Gerber" format is selected.
  • Select Layers F.Cu, B.Cu, F.SilkS, B.Mask, F.Mask, Edge.Cuts
  • Select Options:
  • Plot footprint values
  • Plot footprint references
  • Exclude PCB edge layer from other layers
  • Select Gerber Options:
  • User Protel filename extensions

For Drill file:

  • Units Inches
  • Zeros Format, Suppress leading zeros
  • Drill Map File Format (not used)
  • Drill File Options:
  • Minimal header
  • Merge PTH and NPTH holes into one file
  • Drill origin, Absolute

After export, rename the edge cuts "gm1" extension to "gml" prior to uploading zip to dirtypcbs.com.

Future Revision

Selecting surface 1206 style footprint for C8, the 100uF bypass capacitor for the DRV8805 was a little costly due to needing higher than 12V. An SMD electrolytic would prove significantly cheaper £0.27 vs £2.46 and with a greater voltage margin and not require that much additional space for a radial footprint. Lapse in judgement to be corrected on a future revision.

The power supply could be reduced in size with a more carefully selected inductor. Having never laid out a SMPS however, I decided to stick to the recommended layout and inductors based on the TI regulator used. Further experimentation will be done prior to revision 2 along with a change to SMD electrolytics and diodes.

A surface mounting socket to mate the CAT to the pi would be a better choice as it allows an extended pin leg header to be mounted to the pi and then the CAT mounted on top. This works out cheaper than the elevated sockets.

Signal lines all need test point locations making available.

Switch 4p4c and 6p6c connector layout to socket mounting to allow panel mount option or in the case of a direct wiring, a smaller connector area.

USB ideally should also be panel mount but desoldering the PI's dual sockets is something I'd prefer to avoid.

ST3232 switch to soic version.

Add pin labels to silkscreen for temp port etc current broken square for ground is too hard to see once a pin header is soldered in place.

Add a via behind the regulator to connect ground planes for better thermal relief.

HAT specs for back-powering via 5V GPIO header pin requires addition of an ideal 'safety' diode see design guide

Reference

Copyright

Copyright Gary Preston 2016.

This documentation describes Open Hardware and is licensed under the CERN OHL v. 1.2.

You may redistribute and modify this documentation under the terms of the CERN OHL v.1.2. (http://ohwr.org/cernohl). This documentation is distributed WITHOUT ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING OF MERCHANTABILITY, SATISFACTORY QUALITY AND FITNESS FOR A PARTICULAR PURPOSE. Please see the CERN OHL v.1.2 for applicable conditions