[ale] Sensor nuts

[Chris Fowler]

You came to the conclusion I did initially. I even searched to see if I could rent a 5K device. It is still on my radar. 

forced air is an interesting comment. The application notes for the Sharp do not talk about forcing air. I thought about running a small fan at 5v at reduced speed to imitate breathing via nostrils. That would create some movement. 

I'm redoing a bathroom and about a week ago an idea popped in my head suggesting a powered respirator. Masks suck. I sweat wearing one. 

> From: "Alex Carver" <agcarver+ale at acarver.net>
> To: ale at ale.org
> Sent: Wednesday, June 8, 2016 3:03:11 PM
> Subject: Re: [ale] Sensor nuts

> It's an interesting device but I think it's lacking for what you're
> really attempting to do. The data sheet from Sharp does not make any
> claims about the final particle size that it can potentially detect (not
> measure, that's an important distinction). It mentions just "smoke" in
> the datasheet which is probalby going to be around 1 micron diameter for
> average smoke. However, there are a range of particulates in the air
> that are smaller than 1 micron (the EPA tracks PM10 and PM2.5 which is
> 10 microns and smaller and 2.5 microns and smaller).

> For a short list: Household dust has an expected range of 0.05 - 100
> microns, atmospheric dust (important if windows are open) ranges 0.001 -
> 40, wood smoke is 0.2 - 3, rosin smoke (from solder) is 0.01 - 1,
> tobacco smoke is 0.01 - 4, and anything combustion related including
> cars is 0.01 - 2.5.

> The problem with this detector is that it can't distinguish size, only
> density. So 10 particles at 10 microns diameter is the same as 1
> particle of 100 microns or 100 particles of 1 micron (roughly). It's a
> reflectance measurement so it relies on the total cross section of all
> particles in its field of view and makes an aggregate measurement.

> This sensor will basically be able to tell you "this room is % dusty"
> but it can't say "there's lots of floating hair combined with very fine
> pollen or soot" or "your chimney flue is not open enough and causing
> some smoke to back up into the house". It's also not a forced air
> sensor so sampling is not going to be right since it will depend on dust
> settling into the detector opening.

> What you actually need is a forced air, laser based sensor that can
> distinguish sizes. There are many around that could work within a
> budget and give you some better numbers. Here is one I found with a
> quick search of "laser particulate sensor":

> http://www.dfrobot.com/index.php?route=product/product&product_id=1272&search=SEN0177&description=true

> Or you can get more commercial versions that have more bins for the
> particle sizes:

> http://www.nano-sense.com/en/P4000/p4000-fine-particles-probe.html

> http://www.sens2b-sensors.com/en/item/pm2-5-laser-particle-sensor-module-for-air-purifier-application

> Just keep searching for other options but make sure it bins into various
> sizes instead of lumping everything into a single measurement.
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