20: Nearing the end

So last Friday wasn’t the day…nor was any day this week, however the end is in sight. It’s been a trying week, soldering HDMI cables onto connectors…again…and again inside of a metal box, chasing down potential shorts and generally getting annoyed with some of the design choices I made long ago.

So far I have tested:

  • Motor and power supply. Not a huge achievement here since it was just a case of wiring the things up and flipping a switch but its always good to know I can hook up mains electricity and not kill anyone.
  • Motor driving the shaft with PCB in place. All went well, nothing flew off and I had the board spinning up to 15hz.
  • HDMI through the slip rings. This certainly seems to work, I have so far tested the standard single colours without any parts dropping/distortion and some basic images (more on that in a second).

So everything is spinning nicely and it is mostly lighting up. There are a few issues still to fix:

  • I’ve yet to implement any sort of techometer/rev counter. At the moment it’s a bit of a mess inside the box, with certain components positions not finalised. It occurred to me if using a hall effect sensor and magnet then the magnet needs to be positioned carefully so that it isn’t spinning past any wires because rapidly moving magnets past wires = electronic mayhem. I am probably going to switch over to using IR rather than magnetic rotation sensing to avoid any problems, but for the time being I can just match the shaft speed to frame rate for ~static images.
  • Still need to calibrate the colours. I’m not entirely sure how i’m going to do this, i’m not sure those standard colour calibration tests will translate over to Globe that well.
  • Need to finish tidying up inside the box, make sure everything is strapped down and then put the sides on. To hide all the badness.
  • There is a slight issue with the offset pixels being offset by about 1cm. This is the result of vblank length and the way the code is written. Dropping the length of vblank down will mitigate the problem, switching from the first coding implementation to the third will eliminate it.

So next week is going to be an exciting one, if all goes well and the HDMI is being difficult I will be able to get some of the first proper pictures early on, and then I shall just need to spend the rest tweaking the gamma values for the RGB channels.

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A quick test image. Colours are still wildly off and I need fix a couple of LED channels
2017-08-08 14.19.45
Motor temporarily off to put some rubber washers that David sorted out for me.

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