As well as the microcontroller programming header I added connections for a bluetooth module, I2C attachments and a couple of buttons, I never used them but they add a number of possibilites for control to the project. If I was doing this again I think I would just break out the control pins to a 0.1" header and handle everything else remotely (something to bear in mind if you want to build your own). Unfortunately this IC turned out to be too slow so it had to be removed and I had to connect up an Arduino DUE to the SPI and MOSFET control lines instead. The final part of the schematic is a standalone Arduino consisting of ATMEG328p and supporting circuitry. In theory with all LEDs white a single MOSFET could have to drive almost 4A to a single layer, in practice it is much less than this but this is what I designed the circuit to be capable of.
For this I opted to use a transistor driving a P-Channel MOSFET because of its current drive capabilities. Originally I planned to control 3 data lines each going to 4 STP16s with a common clock and chip select, but this turned out to be slower than a hardware SPI approach, more on this later.īecause the cube is multiplexed the control board needs to be able to turn on and off the individual layers. By dividing 1536 by the 8 layers you end up needing just 192 channels which can also divided by the 16 channels the STP16 offers, leaving the need for just 12 ICs. Instead, to accomplish this the cube has to be multiplexed, meaning only when layer of the cube is ever on at once. The cube itself features 512 RGB LEDs so in total requires 1536 PWM channels, obviously this is not possible using just microcontroller IO pins (Also this would make wiring up the cube very difficult!).
These drivers act as SPI shift registers with a constant current sink feature set by a resistor connected to REXT.
Inspired by a hownottoengineer article I chose to base the design on an STP16 LED driver IC. The schematic for the control board may look complicated but is actually relatively simple.
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