December 12, 2011

page 21 of 23

C-code for main program:

// ALS:

I2C_w_3

(0x38*2, 0x80, 0x03);

// ALS free running mode

I2C_w_3

(0x38*2, 0x86, 0x00);

// new data every 100 ms

I2C_w_3

(0x38*2, 0x98, LB_LL);

// setting low byte of low ALS limit

I2C_w_3

(0x38*2, 0x99, HB_LL);

// setting high byte of low ALS limit

I2C_w_3

(0x38*2, 0x96, LB_HL);

// setting low byte of high ALS limit

I2C_w_3

(0x38*2, 0x97, HB_HL);

// setting high byte of high ALS limit

// Prox:

I2C_w_3

(0x38*2, 0x81, 0x03);

// Prox free running mode

I2C_w_3

(0x38*2, 0x82, 0x1E);

// IR LED with 200 mA

I2C_w_3

(0x38*2, 0x85, 0x00);

// new data every 10 ms

I2C_w_3

(0x38*2, 0x93, Prox_Limit);

// setting byte for high prox limit

I2C_w_3

(0x38*2, 0x92, 0x03);

// interrupt triggered by PS and ALS,

latched and ground when active

// Interrupt routine:

// called when interrupt happened

I2C_w_2_r_1 (0x38*2, 0x8E);

// reading Status Register, Function returns register value as variable Content

if ( (Content & 0x80) == 0x80)

// &=bitwise AND,check whether ALS triggered interrupt

{

I2C_w_2_r_1 (0x38*2, 0x8C);

// read low byte of ADC, register 0xC

Content1 = Content;

I2C_w_2_r_1 (0x38*2, 0x8D);

// read high byte of ADC, register 0xD

Lux = Content * 256 + Content1;

}

Else

// Interrupt must be caused by prox

sensor

{

I2C_w_2_r_1 (0x38*2, 0x8F);

// read Prox data register 0x8F

Prox = Content;

// Value in uW/cm^2 =10power(Content/51)

}

// end of interrupt routine

12.4 Implementation into a Mobile Phone

Environment

Below

are

two

example

flowcharts,

describing how the SFH 7773 can be

implemented into a microcontroller based

mobile phone environment. The interrupt

function allows for low-power stand-alone

operation of the device.

The first flowchart illustrates a possible

operation of the ambient light sensor, the

second flowchart relates to the operation of

the proximity sensor.

12.4.1 Operation of the ALS

Fig. 21 illustrates a flowchart for a

microcontroller based ambient light sensing

example. The interrupt (set to active low)

alerts the microcontroller only in case the

actual ambient light value is outside of the

defined ALS window. Using the interrupt

functionality and operating the SFH 7773 in

the free-running mode helps to minimize

microcontroller from unnecessary work load.

This arrangement helps to save valuable

battery power.

By adapting dynamically new thresholds

(with hysteresis) relative to the actual ALS

value (after an interrupt event took place) it

is possible to define very fine steps for

adapting the display brightness (quasi-

continuous).

By inverting the interrupt polarity (register

0x92) the interrupt alert function can be

inverted from outside the ALS window to