SGP40_CALC_POWER
exp = sgp40_exp(x, SGP40_CALC_POWER, 18);
*voc = 500 * ((1 << (SGP40_CALC_POWER * 2)) / ((1<<SGP40_CALC_POWER) + exp));
*val = voc / (1 << SGP40_CALC_POWER);
*val2 = ((voc % (1 << SGP40_CALC_POWER)) * 244) / (1 << (SGP40_CALC_POWER - 12));