How to put a Dust sensor in a box

Using Arduino Sensors
1

Hi,

I've got a dust sensor SHARP GP2Y10. I want to fix it in the box but I was wondering how the air is measured. I believe looking at the picture online that the air is passing through the hole in the middle. So there is not really a way to hide it.

Thanks

2

The particles are detected inside the hole in the center of the sensor box. That hole has to hold the air to be measured. If the sensor is in a closed case it doesn't have the possibility to detect dust in the surrounding air.

There are several ways to hide the sensor but it cannot be sealed because then the medium to be measured doesn't reach the sensor. What's the reason for hiding it? If you want to just visually hide it put it behind some kind of grid. It usually doesn't put a remarkable resistance to dust but hides visually quite effective.

3

Thanks. So ideally, I would put it on the top of the box to make sure it does receive the particles to measure them. By the way, does anyone know what is good and bad in terms of dust sensor value. I am getting some value but I do not know when is the good and bad air quality.

4

I don't think that you can tell a good or bad limit. It depends on what the particles are. If the particles are water (fog) it not a bad air quality even if the measured values get high (just a bit wet) but if the particles are smoke it might be a health threat even if the measured values are quite low.

5

I am also experimenting with GP2Y1010, and I am seeing some strange results so I wonder if it is the code or the connections maybe creating problems. Have you tried closing the measurement hole on both sides and get reading? According to the datasheet, you should see around 0.9 V with no dust. My sensor, sampling once a second, shows numbers all over the place, from 0 to 1.2 V.

6

That's why I needed to understand the values of the dust sensor:

Here are the values:

230<Raw Signal Value (0-1023)< 282.00 -
0.66<Voltage <0.91
0.01<Dust Density< 0.06

There was not too much difference. Only when there were some wind in the room, I've seen the Raw signal value at 230.

Now, Considering that it the air quality in the room without cooking or doing anything.

What I understood, this is PM10 that we are measuring. There is an interesant post, that I just found.

7

Thanks. In the meantime I found bad connection of the 220uF capacitor, which is what was causing my analogReads to drop to 0 :slight_smile: Now with all the connections good (220 uf - 150 ohm low pass filter as in Sharp datasheet), I get 0.8 V +/- 0.1V (about 165 +/- 20 analogRead value) when both front and back holes are covered, and above that if the holes are open and there is a breeze through home.

Regarding "what do we measure", it is not PM10, neither is it PM2.5 as some e-Bay sellers suggest. What is actually measured is light reflected from particles in the air, and there is no way to tell from a single analogRead if it is reflection off a bunch of tiny particles or off a few of big ones, and equally not what the nature of the particles is (household dust, outside wind-blown dust, pollen, diesel soot, BBQ soot, cigarette smoke...). This is why SHARP correlates the output with the estimated mass of particulates, not the number and/or size of particles. Also keep in mind that a small fan that draws air through the sensor hole would be necessary in order to correctly represent the room air reading. Lastly, some averaging would be necessary for presenting the data (say, of 1-s readings over last minute); EPA requires reporting 1-hour and 8-hour averages that include next 30-min or next 4-hour estimates.

SHARP datasheet suggests that we can infer the particle size from a response curve, but they do not specify how. Our single analogRead does not allow for that; reading that type of information would require much faster sampling than Mega or ARM MCUs can provide. Maybe only XMega with its 2 Msamples could do it. Again, it's empirical and would not provide PM2.5 to PM 10 proportion. That type of data (particle size distribution) is available only from precipitators, which are too big, too noisy, and cost too much.

After all, I'd suggest you house your device in a box of your liking, but provide airflow through the "dust sensor" hole using a very small, quiet, low-speed fan. This is a nice, simple sensor, that gives consistent data, as long as you are OK with what this data tells you - estimated total particulate mass in a given air volume (ug/m3); it does not give ppm, particles per million of other particles, as some of the posts in the link suggest.