Pixel hardware and software

README

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+To make the pixel, 3D print all 7 parts.
+
+The pixel insert (screw) should be in one colour. The case and guide should
+be in a contrasting colour. The small parts can be in any colour, and are
+only visible from the back.
+
+Print one pixel before trying to scale up. Some of these objects are difficult
+to print and will require a well set up 3D printer.
+
+I printed the large parts on an Original Prusa i3 MK2S and the small parts
+on a Creality CR-10. The printing time was of the order of two weeks plus
+failures and spares.
+
+There is some redesigning that would be helpful before scaling up.
+
+The pixel also requires 2 nails and a Tower Pro SG90 servo motor.
+
+Driving the system requires a Pololu Mini Maestro 24-channel USB Servo
+Controller for each 24 servos.
+
+https://www.pololu.com/product/1356
+
+Also required is a suitable 5 volt power supply. I used a Mean Well RS-150-5
+for each servo controller. The worst case current of the servo is around an
+amp, and while the average current will never reach anywhere near that, I sized
+the power supplies accordingly so that they should never shut down due to
+transients. The PCB trace on the servo controller is unlikely to be able to
+handle that much current for long.
+
+Note that the pixel grid will need external mechanical support. I used parts
+from a couple of monitor stands, but any sturdy vertical pole on either side
+should suffice. Black cable ties will then hold it steady.
+
+Assembly should be done carefully. Most parts are push-fit, but that does
+rely on 3D printing tolerances. You may need to slightly adapt some of the
+sizes in the source files to your printer, or be careful about how much
+you file or cut away the rim of the first layer.
+
+Prototyping with a single pixel is essential.