Andy A / wsDrive

Yet another WS2812 driver, uses the BusrtSPI library. Less features than the PixelArray library but I felt like making my own version.

Dependencies:   BurstSPI

Dependents:   WS2812Text cylon

An alternative WS2811/2812 (NeoPixel) driver using the BusrtSPI library.

Credit for the inspiration goes to Jacob Bramley for his pixelArray library that can be found here: http://developer.mbed.org/users/JacobBramley/code/PixelArray/

This version was written mainly to help me understand what was going on rather than to overcome any shortcomings in the other library and as such it lacks some features (800kHz only, no callback on each pixel etc...)

Connect the SPI output to the LED data input, other SPI pins are unused.

Note: The voltage thresholds between the LEDs and mbed devices are on paper incompatible. The datasheet for the WS2812 indicated that running at 5V it requires 4V on Din to count it as a high (the threshold is 0.8*the supply voltage). Most mbeds are lucky to output much over 3.1V. In reality things normally work OK but it depends on the mBed and batch to batch variations in the LEDs, I've seen some combinations that start to fail at an LED supply voltage of 4.4V or more. If something odd is going on try dropping the LED power supply voltage, they run fine down to 4V.

wsDrive.cpp@0:b3665f91bedc, 2014-11-05 (annotated)

Committer:
AndyA
Date:
Wed Nov 05 16:47:48 2014 +0000
Revision:
0:b3665f91bedc
Child:
3:3c48065d20ff
Child:
4:8997e12da7c7
Initial commit. Seems to work for me, needs more comments/documentaion

Who changed what in which revision?

UserRevisionLine numberNew contents of line
AndyA 0:b3665f91bedc 1 #include "wsDrive.h"
AndyA 0:b3665f91bedc 2
AndyA 0:b3665f91bedc 3 wsDrive::wsDrive(PinName mosi, PinName miso, PinName clk) : BurstSPI(mosi,miso,clk)
AndyA 0:b3665f91bedc 4 {
AndyA 0:b3665f91bedc 5 frequency(2400000);
AndyA 0:b3665f91bedc 6 format(12);
AndyA 0:b3665f91bedc 7 pixArray = NULL;
AndyA 0:b3665f91bedc 8 pixelLen = 0;
AndyA 0:b3665f91bedc 9 }
AndyA 0:b3665f91bedc 10
AndyA 0:b3665f91bedc 11 void wsDrive::setData(pixelInfo *dataStart, uint16_t dataLen)
AndyA 0:b3665f91bedc 12 {
AndyA 0:b3665f91bedc 13 pixArray = dataStart;
AndyA 0:b3665f91bedc 14 pixelLen = dataLen;
AndyA 0:b3665f91bedc 15 }
AndyA 0:b3665f91bedc 16
AndyA 0:b3665f91bedc 17 void wsDrive::sendData()
AndyA 0:b3665f91bedc 18 {
AndyA 0:b3665f91bedc 19 frequency(2400000);
AndyA 0:b3665f91bedc 20 format(12);
AndyA 0:b3665f91bedc 21 setFormat();
AndyA 0:b3665f91bedc 22
AndyA 0:b3665f91bedc 23
AndyA 0:b3665f91bedc 24 uint16_t pixIndex = 0;
AndyA 0:b3665f91bedc 25 while (pixIndex < pixelLen) {
AndyA 0:b3665f91bedc 26 sendPixel(pixArray + pixIndex++);
AndyA 0:b3665f91bedc 27 }
AndyA 0:b3665f91bedc 28 }
AndyA 0:b3665f91bedc 29
AndyA 0:b3665f91bedc 30 // each bytes sent as two 12 bit messages (3 bits of data per LED bit).
AndyA 0:b3665f91bedc 31 void wsDrive::sendByte(unsigned char value)
AndyA 0:b3665f91bedc 32 {
AndyA 0:b3665f91bedc 33
AndyA 0:b3665f91bedc 34 uint16_t dataToSend = 0;
AndyA 0:b3665f91bedc 35
AndyA 0:b3665f91bedc 36 uint8_t mask = 0x80;
AndyA 0:b3665f91bedc 37 while (mask) {
AndyA 0:b3665f91bedc 38 dataToSend += (value & mask)?0x06:0x4; // 100 for a 0 or 110 for a 1
AndyA 0:b3665f91bedc 39 if (mask & 0x11) { // trans
AndyA 0:b3665f91bedc 40 fastWrite(dataToSend);
AndyA 0:b3665f91bedc 41 dataToSend = 0;
AndyA 0:b3665f91bedc 42 }
AndyA 0:b3665f91bedc 43 dataToSend = dataToSend << 3;
AndyA 0:b3665f91bedc 44 mask = mask >> 1;
AndyA 0:b3665f91bedc 45 }
AndyA 0:b3665f91bedc 46 }
AndyA 0:b3665f91bedc 47
AndyA 0:b3665f91bedc 48 void wsDrive::sendPixel(pixelInfo *pixToSend)
AndyA 0:b3665f91bedc 49 {
AndyA 0:b3665f91bedc 50 sendByte(pixToSend->G);
AndyA 0:b3665f91bedc 51 sendByte(pixToSend->R);
AndyA 0:b3665f91bedc 52 sendByte(pixToSend->B);
AndyA 0:b3665f91bedc 53 }
AndyA 0:b3665f91bedc 54