VEML6075.cpp

/*
 * VEML6075.cpp
 *
 * Arduino library for the Vishay VEML6075 UVA/UVB i2c sensor.
 *
 * Author: Sean Caulfield <sean@yak.net>
 * 
 * License: GPLv2.0
 *
 */

#include "VEML6075.h"

VEML6075::VEML6075() {

  // Despite the datasheet saying this isn't the default on startup, it appears
  // like it is. So tell the thing to actually start gathering data.
  this->config = 0;
  this->config |= VEML6075_CONF_SD_OFF;

  // App note only provided math for this one, so be advised that changing it
  // will give you "undefined" results from all the calculations.
  // Might be able to do a linear compensation for the integration time length?
  this->config |= VEML6075_CONF_IT_100MS;
}

bool VEML6075::begin(TwoWire *_i2c) {

  this->i2c = _i2c;

  this->i2c->begin();
  if (this->getDevID() != VEML6075_DEVID) {
    return false;
  }

  // Write config to make sure device is enabled
  this->write16(VEML6075_REG_CONF, this->config);

  return true;
}

// Poll sensor for latest values and cache them
void VEML6075::poll() {
  this->raw_uva = this->read16(VEML6075_REG_UVA);
  this->raw_uvb = this->read16(VEML6075_REG_UVB);
  this->raw_dark = this->read16(VEML6075_REG_DUMMY);
  this->raw_vis = this->read16(VEML6075_REG_UVCOMP1);
  this->raw_ir = this->read16(VEML6075_REG_UVCOMP2);
}

uint16_t VEML6075::getRawUVA() {
  return this->raw_uva;
}

uint16_t VEML6075::getRawUVB() {
  return this->raw_uvb;
}

uint16_t VEML6075::getRawDark() {
  return this->raw_dark;
}

uint16_t VEML6075::getRawVisComp() {
  return this->raw_vis;
}

uint16_t VEML6075::getRawIRComp() {
  return this->raw_ir;
}


uint16_t VEML6075::getDevID() {
  return this->read16(VEML6075_REG_DEVID);
}

float VEML6075::getUVA() {
  float comp_vis;
  float comp_ir;
  float comp_uva;

  // Constrain compensation channels to positive values
  comp_ir  = max(this->raw_ir - this->raw_dark, 0);
  comp_vis = max(this->raw_vis - this->raw_dark, 0);
  comp_uva = max(this->raw_uva - this->raw_dark, 0);

  // Scale by coeffs from datasheet
  comp_vis *= VEML6075_UVI_UVA_VIS_COEFF;
  comp_ir  *= VEML6075_UVI_UVA_IR_COEFF;

  // Subtract out visible and IR components
  comp_uva = max(comp_uva - comp_ir, 0.0F);
  comp_uva = max(comp_uva - comp_vis, 0.0F);

  return comp_uva;
}

float VEML6075::getUVB() {
  float comp_vis;
  float comp_ir;
  float comp_uvb;

  // Constrain compensation channels to positive values
  comp_ir  = max(this->raw_ir - this->raw_dark, 0);
  comp_vis = max(this->raw_vis - this->raw_dark, 0);
  comp_uvb = max(this->raw_uvb - this->raw_dark, 0);

  // Scale by coeffs from datasheet
  comp_vis *= VEML6075_UVI_UVB_VIS_COEFF;
  comp_ir  *= VEML6075_UVI_UVB_IR_COEFF;

  // Subtract out visible and IR components
  comp_uvb = max(comp_uvb - comp_ir, 0.0F);
  comp_uvb = max(comp_uvb - comp_vis, 0.0F);

  return comp_uvb;
}

float VEML6075::getUVIndex() {
  float uva_weighted = this->getUVA() * VEML6075_UVI_UVA_RESPONSE;
  float uvb_weighted = this->getUVB() * VEML6075_UVI_UVB_RESPONSE;
  return (uva_weighted + uvb_weighted) / 2.0;
}

uint16_t VEML6075::read16(uint8_t reg) {
  uint8_t msb = 0;
  uint8_t lsb = 0;

  this->i2c->beginTransmission(VEML6075_ADDR);
  this->i2c->write(reg);
  this->i2c->endTransmission(false);

  this->i2c->requestFrom(VEML6075_ADDR, 2, true);
  lsb = this->i2c->read();
  msb = this->i2c->read();

  return (msb << 8) | lsb;
}

void VEML6075::write16(uint8_t reg, uint16_t data) {
  this->i2c->beginTransmission(VEML6075_ADDR);
  this->i2c->write(reg);
  this->i2c->write((uint8_t)(0xFF & (data >> 0))); // LSB
  this->i2c->write((uint8_t)(0xFF & (data >> 8))); // MSB
  this->i2c->endTransmission();
}