Projects

Participants	Brainsmoke
Skills	pcb design, Golang, maths
Status	Finished
Niche	Electronics
Purpose	World domination

Idea: make a quad copter with lots of addressable RGB LEDs

Stage 1: Ledball hardware (completed)

pick a shape

A Catalan solid is a polyhedron with faces which are all identical (but its vertices are not.)

This is a nice property for a ball made out of PCBs, as you only need to order one shape of PCB.

I Picked the deltoidal hexecontahedron because it looked pretty.

napkin calculation

As my ledball should become a flying Death^WDay star at night, I wanted to use lots of LEDs. Powering them over 5V would mean lots of amps. I chose to drive the LEDs per three by putting them in series. This allows the LEDs to be powered reasonably efficiently using 11.1V (3 Cell LiPo) or 12V (ATX PSU.)

This does preclude the use of WS2812B (neopixel) LEDs, so I went for external WS2801 driver chips

The deltoidal hexecontahedron has 60 faces
5 WS2801 drivers per face
3 LEDs in series per driver
max 20mA per colour, 3 colours

>>> 60*5*3*.02
18 # Amps
>>> _*12
216 # Watt

Calculate pcb shape

The code I wrote to generate the PCB shape:

github.com/brainsmoke/dhxdron

It generates an SVG shape based on a given radius (of the inscribed sphere) of the polyhedron and the material thickness. The material thickness is used to generate a notched edge which locks at precisely the right angle.

The script also generates slots for the tie-wraps that will hold the ball together.

Script to generate kicad module from SVG PCB shape

github.com/brainsmoke/pathtokicad

Positioning the LEDs

KiCAD PCB design

github.com/brainsmoke/polyhedrone

Schematic

PCB

Bill of materials

quantity	package	part	comment
60x		PCB	ordered 100x 2 layer, 10^2cm max, .6mm, white HASL @ Seeedstudio
300x	SOIC14	WS2801 Led Driver	Ledsee
900x	5050	RGB LED SMD	ordered: 1000x Samsung SPMFCT5606N0S0A1E0 (Nice color balance) @ Ledsee
900x	1206	Resistor 33 Ohm	use 30 Ohm for 20 mA/color (max specced brightness)
300x	0805	100nF Capacitor
12x	SOT223	AMS1117-3V3 voltage regulator	Ledsee
1x		Raspberry Pi B+
1x		200+ Watt (400 Watt) ATX PSU

Soldering & Testing

Test program

 #include <SPI.h>
 
 void setup()
 {
     SPI.begin();
     SPI.setBitOrder(MSBFIRST);
     SPI.setDataMode(SPI_MODE0);
     SPI.setClockDivider(SPI_CLOCK_DIV16);
 }
 
 void fill_colour(uint8_t r, uint8_t g, uint8_t b)
 {
     uint16_t i;
     for (i=0; i<500; i++)
     {
         SPI.transfer(r);
         SPI.transfer(g);
         SPI.transfer(b);
     }
 }
 
 void fill_back(uint8_t r, uint8_t g, uint8_t b)
 {
     uint16_t i;
     uint8_t j;
     for (i=0; i<100; i++)
     {
         for (j=0; j<12; j++)
             SPI.transfer(0);
 
         SPI.transfer(r);
         SPI.transfer(g);
         SPI.transfer(b);
     }
 }
 
 void loop()
 {
 
     for(;;)
     {
         fill_colour(255, 0, 0);     // Red
         delay(500);
         fill_colour(0, 255, 0);     // Green
         delay(500);
         fill_colour(0, 0, 255);     // Blue
         delay(500);
         fill_colour(255, 255, 255); // White
         delay(500);
         fill_back(255, 0, 0);
         delay(500);
         fill_back(0, 255, 0);
         delay(500);
         fill_back(0, 0, 255);
         delay(500);
         fill_back(255, 255, 255);
         delay(500);
         fill_colour(0, 0, 0);        // Black
         delay(500);
     }
 }