5 thoughts on “Polargraph SD interface

  1. You’re quite mad, you know.

    Where will it all end? Today a touchscreen interface, tomorrow an iPhone app that allows someone to snap a photo and send it their machine from around the world. Get to work on the automatic rolled paper feeder and pen capping mechanism, or the InstaPolarGram will never happen!

    • Ha! You think you’re joking! Yes the automatic stuff will be tricky. Pen capping is a good idea though. I always imagined a kind of docking station .. but an automatic cap would be better, rather like the automatic capping mechanism in a retractable sharpie. Self calibration is the other half of that problem, but that’s easier to solve I think.

      Really, the reason for the touch-screen is that it happened to include all the buttons and indicators I could need, along with a SD card slot and a versatile electrical interface, and cost no more than all those components discretely, as well as being much less complex to assemble.

      It is coincidence that it happens to be rad.

  2. Man that is so cool. I am very interested in what or how you got all that together. I have a mega just wanting to be used. Does it work well? How did you connect it?
    Great job!

    • Not quite there yet Matt, just a teaser! At the moment there’s a simple shield between the mega and the screen, because it pulls about 24-odd pins from all over the place into a big 40 pin connector. It means that I can’t get a motorshield in anywhere and I haven’t got a discrete step-stick-based circuit ready to test with… So it’s only driving imaginary motors for now.

      But I’m eventually going to have the display on a short (couple of inches) long bit of ribbon cable, or at the very least positioned out of the way. In fact, I got an IDE cable to do just that, but forgot IDE connectors have a keying pin blanked out in the middle! So annoyed.

      Code wise, I _think_ I’ve got it figured out ok. There’s a library for driving the TFT itself that does simple graphics and text, and a second library for reading the touch – both pretty straightforward (from http://henningkarlsen.com/electronics/library.php) though the touch library needed a little convincing to work. The touch interface is connected to one of the arduino interrupts, so it can be used fairly unintrusively (once I’d figured to mark the variables as volatile). Which means the rest is up to me to write the code in a sensible way. It was never written with this kind of realtime control in mind so it’s not a great “fit”, so I feel a code restructure/rewrite is looming but I’m going to hack the next working version together and worry about efficiency / prettiness at a later date. That looming feeling has been looming for some time now.

      The screen is pretty slow (for updating), but it’ll do, and probably a lot more useful than a bunch of LEDs and some badly wired buttons. My EE is very weak, so the more things are bundled up into neat packages, the better – for all of us.


  3. Awesome, that’s just sick man. Keep up the great work. I got more and more people asking me to make drawings for them each week. These machines are really getting popular!

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