As7341 spectrum sensor measures color temperature color_ temperature_ Study notes

AS7341 brief introduction

（1） Its spectral response is defined at about 350nm to 1000nm Wavelength range , Eight optical channels cover the visible spectrum , One channel can be used to measure near-infrared light （NIR）, One channel is a photodiode without a filter （C）. The combination of near-infrared light channel and other visible light channels can provide ambient light conditions （ The light source ） Detected information .

（2） The six channels can be independent 16 position ADC parallel processing , Other channels are accessed through multiplexers .

（3） The device also integrates a dedicated channel , Can be detected 50Hz or 60Hz Ambient light flashes , The flicker detection engine can also be used to buffer data when calculating other flicker frequencies externally .

（4） The device can also pass through pins GPIO Synchronize with external signals .

（5） Small size and low power spectral sensor .

Measurement principle

We can use it directly AMS The correction data of mass production of sensors provided and based on CIE1931 Of XYZ Modify the matrix to calculate the color temperature ,XYZ The correction matrix is shown in the following table 2.CIE1931XYZ In the primary color system X、Y、Z The value of can be calculated according to the following formula （3）：

CIE1931xyz Relative coefficient in color space x、y、z The following formula can be used （4） Calculation ：

Color temperature calculation formula ：

Color temperature detection function

// Need a parameter ：spectraNum[10] Array 
//spectralNum[10], Stored F1-F8 and Clear,NIR The data of 
int color_temperature(unsigned int *spectralNum)
{
    
	float X,Y,Z,x,y,n,cdc;
	
	X=0.39814*spectralNum[0]+	1.29540*spectralNum[1]+	0.36956*spectralNum[2]+	0.10902*spectralNum[3]+	0.71942*spectralNum[4]+	1.78180*spectralNum[5]+	1.10110*spectralNum[6]	-0.03991*spectralNum[7]	-0.27597*spectralNum[8]	-0.02347*spectralNum[9];
	Y=0.01396*spectralNum[0]+	0.16748*spectralNum[1]+	0.23538*spectralNum[2]+	1.42750*spectralNum[3]+	1.88670*spectralNum[4]+	1.14200*spectralNum[5]+	0.46497*spectralNum[6]	-0.02702*spectralNum[7]	-0.24468*spectralNum[8]	-0.01993*spectralNum[9];
    Z=1.95010*spectralNum[0]+	6.45490*spectralNum[1]+	2.78010*spectralNum[2]+	0.18501*spectralNum[3]+	0.15325*spectralNum[4]+	0.09539*spectralNum[5]+	0.10563*spectralNum[6]+	0.08866*spectralNum[7]	-0.61140*spectralNum[8]	-0.00938*spectralNum[9];
	
	x=X/(X+Y+Z);
    y=Y/(X+Y+Z);

	
    n=(x-0.3320)/(0.1858-y);
    cdc=437*n*n*n+ 3601 *n*n +6831 *n+ 5517;
	return (int)cdc;
	
}

Reference article

[1] Wang Wei .AS7341 Analysis and research of spectral sensor [J]. Electronic testing ,2021(13):59-61.DOI:10.16520/j.cnki.1000-8519.2021.13.018.

[2]STM32F103 Use AS7341 Spectrum detection sensor driver