A project log for StarPi

A Raspberry Pi based Astrophotography System

ChrisChris 02/21/2018 at 22:060 Comments

I've spent some time working on the installation of StarPi. I tracked down the Malloc issue in the installation, I think this was caused by a conflict in GPSD version. I had an extra step in the GPSD install, which I didn't need. I've also tidied up the install script and makefile. It should finally now be possible for people to replicate. It still needs quite a bit of configuration for the choice of hardware, but I've defaulted it to the LSM303DLHC in a particular orientation to the telescope. I chose the LSM303DLHC as I found some breakout boards fairly cheap along with a cheap GPS breakout. These with the Zero W have brought the cost down considerably. 

The second problem I've sorted has is an issue with the co-ordinate calculations. I found the ERFA library, which is the SOFA library with all the appropriate credits for the licence. This was fairly simple to add, but i did make it into a C++ class from C. The operation was better, but still not quite right. I started to debug the problem and discovered it was coming from the compass. while I was debugging I wasn't really able to get repeatable results, so I built myself a jig:

It's made from scrap bits of laser ply from other projects and a load of BB pellets to act as bearings. There's two slots added to let a piece of 3 mm ply cut to an angle to lock the sensor bar in place. I've cut a few different angles to test with. This has let me debug and check the orientation calculation is OK. There is some offset in the magnetic heading when compared with a compass so a little calibration needs to be added. I then went back to the telescope and checked how accurate it was when pointed at the sky. I got the telescope pointed at Rigel and took a screenshot:

There is definitely some calibration needed It's pointing to RA/DEC 4h59m30.82s/-9*27'16.5" when the Rigel was actually at RA/Dec 5h14m32.28s/-8'11*05.9". To add access to do this calibration I've started working on a socket interface that will also act as the interface to an ASCOM driver. This has replaced the websocketd interface. Eventually this will allow both the driver and a website to access the data. I've done some testing of the interface, but I've not yet updated the website to and have decided not to for the moment as I'm concentrating on the ASCOM driver when the sky is cloudy and still trying to get a photo of the stars when the sky is clear!