100lux * IR42   100 * IR42(mA)
Ev (illuminance in lux) = ------------- = --------------
                           Ipce@100lux      0.02325mA

                       Ain * 3.3
                       ---------
                          11             Ain * 3.3   Ain * 330   Ain * 30
      Ev (lux) = 100 * --------- = 100 * --------- = --------- = --------
                         Ipce            11 * Ipce   11 * Ipce     Ipce

R42 = 1k => VR42 @ 1lux    = 232.5nA * 1000 = 232.5uV  => AMBLGHT_LVL = 11 x VR42 = 2.5575mV
            VR42 @ 1000lux = 232.5uA * 1000 = 232.5mV  => AMBLGHT_LVL = 11 x VR42 = 2.5575V

Extrapolate to full scale (3.3V) - Max. level = 1290 lux.

1lux    = 232.5nA - 50nA = 182.50nA (21.5% error)
1000lux = 232.5uA - 50nA = 232.45uA

Calibrate function : We take 10 consecutive samples discarding samples > 0.000050

                     ds   = discarded samples
                     sa   = sum of samples
                     ns   = number of samples     = 10
                     amp  = opamp amplification   = 11
                     Vref = DAC reference voltage = 3.3V

                     If ds = ns : set dark_current = 0

                                         (sa / (ns - ds)) * Vref   (sa / (ns - ds)) * 3.3     sa * 3.3
                     dark_current (mA) = ----------------------- = ---------------------- = ------------
                                                    amp                       11            (ns-ds) * 11

Ain  = Analog input value read from input (float) 0.0 .. 1.0
amp  = opamp amplification
Vref = DAC reference voltage (V)
Ipce = theoretical average current @ 100lux (mA)
dc   = averaged dark current obtained from calibrate() function (mA)

                       Ain * Vref
                       ----------
                          amp      100 * Ain * Vref
      Ev (lux) = 100 * --------- = -----------------
                       Ipce - dc   amp * (Ipce - dc)

#define TEMT_AREF          (float)3.3           // Analog reference voltage
#define TEMT_MAXLX         1290                 // Calculated max. lux
#define TEMT_AMP           11                   // Op-amp amplification
#define TEMT_IAVG          (float)0.02325       // Theoretical average Ipce @ 100lux
#define TEMT_DARKC         (float)0.000050      // Max. dark current


Used in our formula : Vref = TEMT_AREF
                      amp  = TEMT_AMP
                      Ipce = TEMT_IAVG

#include "TEMT6200.h"
#include "ComparatorIn.h"
#include "mbed.h"

void ambi_rise(void);       // ISR callback pointer
void ambi_fall(void);       // ISR callback pointer

// RGB LED
DigitalOut cmpled (LED_GREEN);
DigitalOut blinky (LED_BLUE);

// Ambient light sensor to comparator plus input = PTC8, min input = 12-bit DAC0
ComparatorIn compi(PTC8, PTE30);

// Ambient light sensor : PTD5 = enable, PTB0 = analog input
TEMT6200 ambi(PTD5, PTB0);

int main()
{
    // Ambient light detector
    ambi.pwr(AMB_ON);
    printf("\n- Ambient light sensor calibration.\n");
    printf("  Make sure the sensor is obscured .\n");
    printf("  Press any key to calibrate.\n");
    getchar();
    ambi.calibrate();                                 // Calibrate 
    printf("- Calibration finished.\n");

    // Comparator settings
    compi.rising(&ambi_rise);                         // Set comparator rising int callback to ambi_rise
    compi.falling(&ambi_fall);                        // Set comparator falling int callback to ambi_fall
    compi.treshold(ambi.lux_pct(300.0));              // Set ISR treshold to 300lux
    compi.int_en(1);                                  // Enable comparator interrupt

    cmpled = 1;
    
    while (1)
    {
        printf("%7.2f lux\n",ambi.read());
        wait(0.5);
        blinky = !blinky;
    }
}

// Comparator callback
void ambi_rise(void)
{
    cmpled = 0;                       // Green led on.
}

void ambi_fall(void)
{
    cmpled = 1;                       // Green led off.
}