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A project log for StarPi

A Raspberry Pi based Astrophotography System

ChrisChris 08/21/2016 at 21:430 Comments

My replacement coupling arrived, I'd chosen a flexible coupling, but something had got lost in translation. The shaft diameters were both wrong. Fortunately the Maker Space has a Lathe. As a member I've helped get this up and running but not had a chance to use it yet. This was an ideal opportunity to try it out, and bore out the shaft diameter of the coupling. It was definitely the right tool for the job. I very quickly had the shafts coupled. I then mounted the motor to the mount, using the parts I'd already made. I gave it a quick test using a 12V supply. The top speed was high enough, I'm more interested in the slow end of the scale as I don't need much to keep it aligned to a position.

Since my last post I've been to the Electromagnetic field festival in Guildford. I took StarPi to the Hackaday meetup to show what I've done. I really enjoyed meeting everyone and seeing the other projects that were brought and thanks to Hackaday, the free flowing beer was good too! I had a chat with a few people about StarPi and got some really good feedback about what I've done. The night skys at the festival were nice and clear and since I had the telescopes out I had a little experiment with the Pi camera to see If i was better off with the lens on or off and with or without the IR filter. Sadly I think there was too much ambient light to be able to see any of the stars, so I postponed it for a later date.

I began to add some motor control to the project. This consisted of an interface to the LM298 that I'm using to drive the motors using the gpio and hardware PWM of the Pi and a PID control loop. The PID Is a port of the Arduino PID library. I've started to test the LM298 interface, but have so far failed to create a PWM signal from the B+ that I have. I've not looked into why yet, as I have decided to split up the project. The Raspberry Pi is currently doing quite a few tasks and I'm suspicious that the OS will start to get in the way of the control loops when heavily loaded with the plate solving. I've split the project into two parts. The Raspberry Pi will handle the Camera and Website, with the ability to run other tools, including the Plate solving and the correction for magnetic declination. I'm going to use a micro-controller to run the real time side of things. This will run the sensors and calculate the position on the sky map and take commands from the website to control the tracking.

The board I've chosen to do this, is one I was given as a result of using a Wiznet part in the Hackaday Prize 2014. I was sent a WIZwiki-W7500 development board. This is an mbed enabled ARM board with on board hardware TCP/IP core that can handle up to 8 Sockets and has all the typical peripherals that you'd expect. I've began porting the project to the mbed, which is going well. The total work is to tweak the interface to the hardware, write a replacement for GPSD and write a socket handler for the website and Stellarium. If all goes well, I'm hoping to be able to spin a PCB for some dedicated hardware.

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