Based on code of Bob Kojima 01-19-2008 further modified by Roland Wiersma
Original link is dead: http://www.rjw.speedxs.nl/arduino/LEGOPowerFunctions.rar Mirror: http://basbase.com/robocam/LEGOPowerFunctions.zip
I was planning on creating my own library to control LEGO Power Functions using an IR LED attached to an arduino and/or Raspberry pi but I found this as a starting point. The library seems to have been written prior to V1.0 of the Arduino software since it references WProgram.h. Other than this single zip file I have found only a few references of this library and it's original author.
//SinglePin & SingleOutput modes
#define CONTINUOUS 0x2
#define TIMEOUT 0x3
#define PWM 0x0
#define CST 0x2 //Clear - Set - Toggle
//ComboPWM & SingleOutput pwm steps
#define PWM_FLT 0x0
#define PWM_FWD1 0x1
#define PWM_FWD2 0x2
#define PWM_FWD3 0x3
#define PWM_FWD4 0x4
#define PWM_FWD5 0x5
#define PWM_FWD6 0x6
#define PWM_FWD7 0x7
#define PWM_BRK 0x8
#define PWM_REV7 0x9
#define PWM_REV6 0xA
#define PWM_REV5 0xB
#define PWM_REV4 0xC
#define PWM_REV3 0xD
#define PWM_REV2 0xE
#define PWM_REV1 0xf
//SingleOutput Clear - Set - Toggle steps
#define CL_C1_CL_C2 0x0
#define ST_C1_CL_C2 0x1
#define CL_C1_ST_C2 0x2
#define ST_C1_ST_C2 0x3
#define INC_PWM 0x4
#define DEC_PWM 0x5
#define FULL_FWD 0x6
#define FULL_REV 0x7
#define TOG_FWD_REV 0x8
//ComboMode steps
#define RED_FLT 0x0
#define RED_FWD 0x1
#define RED_REV 0x2
#define RED_BRK 0x3
#define BLUE_FLT 0x0
#define BLUE_FWD 0x4
#define BLUE_REV 0x8
#define BLUE_BRK 0xC
//channels
#define CH1 0x0
#define CH2 0x1
#define CH3 0x2
#define CH4 0x3
//SinglePin & SingleOutput output
#define RED 0x0
#define BLUE 0x1
//SinglePin functions
#define NO_CHANGE 0x0
#define CLEAR 0x1
#define SET 0x2
#define TOGGLE 0x3
//SinglePin pin
#define PIN_C1 0x0
#define PIN_C2 0x1
PowerFunctions(int IR_Pin);
void SingleOutput(int mode, int step, int output, int channel);
void SinglePin(int mode, int function, int pin, int output, int channel);
void ComboMode(int blue_speed, int red_speed, int channel);
void ComboPWM(int blue_pwm, int red_pwm, int channel);