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• General technical description

  max.mali • 07/03/2014 at 15:04 • 0 comments

  The most import thing for being able to generate proper animations in multiple
  colours is that it is possible to control every single colour of the 1024 LEDs
  separately. This means that it is possible to turn on red and green (=yellow) on one
  RGB LED while on another LED only blue is turned onfor example.
  To achieve this, a lot of LED drivers, which basically are shift registers with some
  additional control logic so that only one resistor is needed to adjust the current for
  all LEDs on one driver, are needed.
  All 32 layers with the LEDs on them are rotated around a common axis with 20rps.
  The necessary brushless DC motor has got an internal control logic built into it and
  can be controlled over a couple of simple digital inputs whose function can be preprogrammed.
  One full rotation is separated into 1024 individual"refreshes" for all LEDs, where
  they are able to change their colours, so that 3D pictures or animations can be
  displayed. The refreshes occur when an optical forksensor passes by a tooth of a
  fix mounted crone, which has one tooth for each refresh. When a refresh occurs all
  LED drivers are filled with new pre calculated dataand once the shift registers are
  full the data is shifted out to the LEDs. Knowing which animation is supposed to be
  displayed, the data can be calculated and stored onan external flash memory
  before displaying it earlier.
  Because of the huge amount of data and LEDs a single microcontroller would not
  be fast enough to put out the new data for every refresh in time. Besides too many
  microcontroller pins would be needed to connect allof the electrical components.
  For this reason every single layer has its own microcontroller and its own flash
  memory. This way the data can be loaded from the flash and put into the LED
  drivers 32 times faster than with just one microcontroller and also the number of
  pins needed are no problem anymore. The practical thing about this solution is
  that the hardware layout design and the firmware are the same for all of the 32
  layers.
  To save all the animation data in the different flash memories an additional
  microcontroller, which is the master of all the other (slave) microcontrollers on the
  layers, is needed. The master is connected to the slaves per an modified SPI bus
  with two additional bus wires. The addresses of theindividual layers are the only
  things which alter from layer to layer. However this is necessary so that the master
  controller is able to select each layer for data transfer individually. To make it
  possible to use the same hardware and firmware for all layers the same 5 I/O pins
  of the slave controllers are used to set the address. All of them are pulled to
  ground by default after production. The only thing that needs to be done to set the
  addresses is to connect the traces between the individual I/0 pins and V+
  differently for each layer (5 traces -> 32 possibilities). The firmware scans if the I/O
  pins are connected to V+ or not and sets a bit maskwhich represents the address
  according to the connections then.
  All of the animation data has to be sent to the master controller before it can be
  passed along to the slaves with the SPI bus. The data transmission between a PC,
  which already stores all of the necessary data, andthe master controller is
  achieved per USB.
  Actually one more additional microcontroller is needed because the motor doesn't
  rotate along with the LEDs. The motor is wired to the so called "base board", which
  is the only board which doesn't rotate, along with an LC display which is needed
  for control purposes. The LCD offers an easy to operate 4 button GUI where the
  different animations can be selected, paused and rotated and brightness can be
  adjusted. The data between the master controller (main board) and the base
  controller can't be transmitted per wires because the base board is fixed and the
  main board rotates. To make a communication betweenthese two possible one
  Bluetooth module is needed on each board. Because one module can only...

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