hal_Osram_SFH5711_ambient_light_sensor.c File Reference

Conversion routines for the Osram SFH5711 Ambient Light Sensor. More...

#include <math.h>


#define	LIGHT_SENSOR_USE_LOOKUP_TABLE
unsigned int	convertAdcToLux (unsigned int adc)

Detailed Description

Conversion routines for the Osram SFH5711 Ambient Light Sensor.

Note:

Light sensor outputs current between 0 to 50uA. On the target board, load resistor = 47k Ohms.

0 to 100,000lx will generate 0 to 2350mV input into an Analog to Digital Converter (ADC).

This particular light sensor is binned for a sensitivity of 27 to 30 uA @ 1000lux = 1269-1410 mV = ADC readings of 520-578counts

there are two versions of the convertAdcToLux() method:

Use a lookup table. Faster and less code, but also less accurate.
Compute the value directly based on equation supplied by the manufacturer. This is much more accurate but requires approximately 4.2kB more code for the pow() function in math.h.

Rev: 545

Author: dsmith

Date: 2010-05-27 17:09:05 -0700 (Thu, 27 May 2010)

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Function Documentation

unsigned int convertAdcToLux ( unsigned int adc )

Converts the raw ADC value to lux for the Osram SFH 5711 light sensor using pow() method in math.h. Conversion:

Convert ADC to millivolts: mV=(ADC/1024) * 2500 (10bit ADC = 1024counts; we're using the 2.5V reference)
Convert millivolts to microAmps: uA = mV / 47 (since the design uses a 47kOhm load resistor)
Convert microAmps to lux: lux = 10^(uA/10)
Parameters:

adc the raw reading from the Analog to Digital converter

Returns:
the amount of light, in lux/10.