Light scattering measurement based on multiple light sources

1 . An apparatus comprising:

a first light source configurable to generate a first light signal having a first wavelength;

a second light source spaced from the first light source and configurable to generate a second light signal having a second wavelength, the second wavelength different from the first wavelength;

a light detector having a detector output, the light detector configurable to:

generate a first detection signal at the detector output responsive to the first light signal; and

generate a second detection signal at the detector output responsive to the second light signal; and

a processing circuit having a processing input and a processing output, the processing input coupled to the detector output, and the processing circuit configurable to generate a third signal representative of an air quality measurement at the processing output responsive to the first and second detection signals, wherein the third signal represents at least one of: a particle size or a mass concentration of particles.

2 . The apparatus of claim 1 , wherein the processing circuit is configurable to:

determine an intensity ratio between the first light signal and the second light signal received by the light detector based on the first and second detection signals; and

determine the particle size based on the intensity ratio.

3 . The apparatus of claim 1 , wherein the processing circuit is configurable to determine the particle size based on at least one of: a polynomial function that relates particle sizes and intensity ratios, or a mapping between particle sizes and intensity ratios.

4 . The apparatus of claim 1 , wherein the processing circuit is configurable to determine the mass concentration based on the particle size.

5 . The apparatus of claim 1 , wherein the processing circuit is configurable to:

determine a received intensity of at least one of the first or second light signals at the light detector based on at least one of the first or second detection signals;

determine an expected single particle scatter intensity of the at least one of the first or second light signals based on the particle size;

determine a particle concentration based on a ratio between the received intensity and the expected single particle scatter intensity; and

determine the mass concentration based on the particle concentration.

6 . The apparatus of claim 1 , wherein the first wavelength is in an infrared spectral region and the second wavelength is in a blue spectral region.

7 . The apparatus of claim 1 , wherein the first light source is configurable to project the first light signal at a first angle with respect to the light detector, and the second light source is configurable to project the second light signal at a second angle with respect to the light detector, such that the first light signal is backscattered at a third angle in a range of 50 to 60 degrees with respect to the projection of the first light signal by the first light source, and the second light source is backscattered at a fourth angle in a range of 145 to 155 degrees with respect to the projection of the second light signal by the second light source.

8 . The apparatus of claim 1 , wherein the processing circuit comprises a microcontroller unit (MCU) including a controller input and a controller output, the controller input being coupled to the processing input, and the controller output being coupled to the processing output, and wherein the MCU is configurable to: receive, at the controller input, the first and second detection signals; and provide, at the controller output, the third signal representative of the air quality measurement.

9 . The apparatus of claim 1 , wherein the first light source and the second light source are oriented at different angles with respect to the light detector.

10 . An apparatus comprising:

a processing circuit having a processing input and a processing output and configurable to:

receive a first detection signal at the processing input, the first detection signal representing detection of a first light signal from a first light source, the first light signal having a first wavelength;

receive a second detection signal at the processing input, the second detection signal representing detection of a second light signal from a second light source spaced from the first light source, the second light signal having a second wavelength; and

generate a third signal representative of an air quality measurement at the processing output responsive to the first and second detection signals, wherein the third signal represents at least one of: a particle size or a mass concentration of particles.

11 . The apparatus of claim 10 , wherein the processing circuit is configurable to:

determine an intensity ratio between the first light signal and the second light signal based on the first and second detection signals;

determine the particle size based on the intensity ratio; and

determine the mass concentration based on the particle size.

12 . The apparatus of claim 10 , wherein the processing circuit is configurable to determine the particle size based on at least one of: a polynomial function that relates particle sizes and intensity ratios, or a mapping between particle sizes and intensity ratios.

13 . The apparatus of claim 10 , wherein the processing circuit is configurable to:

determine a received intensity of at least one of the first or second light signals based on at least one of the first or second detection signals;

determine an expected single particle scatter intensity of the at least one of the first or second light signals based on the particle size;

determine a particle concentration based on a ratio between the received intensity and the expected single particle scatter intensity; and

determine the mass concentration based on the particle concentration.

14 . A method comprising:

transmitting, with a first light source, a first light signal having a first wavelength;

transmitting, with a second light source spaced from the first light source, a second light signal having a second wavelength different from the first wavelength;

generating, by a light detector, a first detection signal responsive to the first light signal;

generating, by the light detector, a second detection signal responsive to the second light signal; and

generating, by a processing circuit, a third signal representative of an air quality measurement responsive to the first and second detection signals, wherein the third signal represents at least one of: a particle size or a mass concentration of particles.

15 . The method of claim 14 , further comprising:

determining an intensity ratio between the first light signal and the second light signal based on the first and second detection signals;

determining the particle size based on the intensity ratio; and

determining the mass concentration based on the particle size.

16 . The method of claim 14 , further comprising determining the particle size based on at least one of: a polynomial function that relates particle sizes and intensity ratios, or a mapping between particle sizes and intensity ratios.

17 . The method of claim 14 , further comprising:

determining a received intensity of at least one of the first or second light signals based on at least one of the first or second detection signals;

determining an expected single particle scatter intensity of the at least one of the first or second light signals based on the particle size;

determining a particle concentration based on a ratio between the received intensity and the expected single particle scatter intensity; and

determining the mass concentration based on the particle concentration.

18 . A non-transitory computer readable medium storing instructions that, when executed by a processor, cause the processor to:

receive a first detection signal, the first detection signal representing detection of a first light signal from a first light source, the first light signal having a first wavelength;

receive a second detection signal, the second detection signal representing detection of a second light signal from a second light source spaced from the first light source, the second light signal having a second wavelength; and

generate a third signal representative of an air quality measurement responsive to the first and second detection signals, wherein the third signal represents at least one of: a particle size or a mass concentration of particles.

19 . The non-transitory computer readable medium of claim 18 , wherein the instructions cause the processor to:

determine an intensity ratio between the first light signal and the second light signal based on the first and second detection signals;

determine the particle size based on the intensity ratio; and

determine the mass concentration based on the particle size.

20 . The non-transitory computer readable medium of claim 18 , wherein the instructions cause the processor to determine the particle size based on at least one of: a polynomial function that relates particle sizes and intensity ratios, or a mapping between particle sizes and intensity ratios.

21 . The non-transitory computer readable medium of claim 18 , wherein the instructions cause the processor to:

determine a received intensity of at least one of the first or second light signals based on at least one of the first or second detection signals;

determine an expected single particle scatter intensity of the at least one of the first or second light signals based on the particle size;

determine a particle concentration based on a ratio between the received intensity and the expected single particle scatter intensity; and

determine the mass concentration based on the particle concentration.