TSL2581, TSL2583
LIGHT-TO-DIGITAL CONVERTER
TAOS134 − MARCH 2011
22
r
r
Copyright E 2011, TAOS Inc.
The LUMENOLOGY r Company
www.taosinc.com
// lux equation approximation without floating point calculations
//////////////////////////////////////////////////////////////////////////////
// Routine: unsigned int CalculateLux(unsigned int ch0, unsigned int ch0, int iType)
//
// Description: Calculate the approximate illuminance (lux) given the raw
// channel values of the TSL2583. The equation if implemented
// as a piece−wise linear approximation.
//
// Arguments: unsigned int iGain − gain, where 0:1X, 1:8X, 2:16X, 3:128X
// unsigned int tIntCycles − INTEG_CYCLES defined in Timing Register
// unsigned int ch0 − raw channel value from channel 0 of TSL2583
// unsigned int ch1 − raw channel value from channel 1 of TSL2583
// unsigned int iType − package type (1:CS)
//
// Return: unsigned int − the approximate illuminance (lux)
//
//////////////////////////////////////////////////////////////////////////////
unsigned int CalculateLux(unsigned int iGain, unsigned int tIntCycles, unsigned int ch0,
unsigned int ch1, int iType)
{
//−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
// first, scale the channel values depending on the gain and integration time
// 1X, 400ms is nominal setting
unsigned long chScale0;
unsigned long chScale1;
unsigned long channel1;
unsigned long channel0;
// No scaling if nominal integration (148 cycles or 400 ms) is used
if (tIntCycles == NOM_INTEG_CYCLE)
chScale0 = (1 << CH_SCALE);
else
chScale0 = (NOM_INTEG_CYCLE << CH_SCALE) / tIntCycles;
switch (iGain)
{
case 0: // 1x gain
chScale1 = chScale0; // No scale. Nominal setting
break;
case 1: // 8x gain
chScale0 = chScale0 >> 3; // Scale/multiply value by 1/8
chScale1 = chScale0;
break;
case 2: // 16x gain
chScale0 = chScale0 >> 4; // Scale/multiply value by 1/16
chScale1 = chScale0;
break;
case 3: // 128x gain
chScale1 = chScale0 / CH1GAIN128X; //Ch1 gain correction factor applied
chScale0 = chScale0 / CH0GAIN128X; //Ch0 gain correction factor applied
break;
}
// scale the channel values
channel0 = (ch0 * chScale0) >> CH_SCALE;
channel1 = (ch1 * chScale1) >> CH_SCALE;
//−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
// find the ratio of the channel values (Channel1/Channel0)
// protect against divide by zero
