Looking for novel ways to create an air flow for dust or air quality sensor

Question

I'm looking at various dust sensors for a home monitoring application - one location would be a bedroom.

I noticed that some of these sensors, such as Omron's B5W-LD0101 sensor, for example, include a resistor inside the sensor which acts as a heater to generate an air flow or air drift past the optical sensor which then measures the particulate density.

Some others, such as Sharp's GP2Y10## do not include heaters.

The Sharp sensor is attractive because of low cost.

I now want to explore novel ways to generate air flow to improve measurement quality with a Sharp Air Quality sensor.

One idea I had, but have not sure if it would work, was to use an ultrasonic sensor, such as the cheap HC-SR04 to gently agitate a surface to "move" air flow through the inlet. I know you get ultrasonic cleaners but I thought that if the ultrasonic pulse is low power it certainly won't clean but maybe it would at least agitate air / dust particulates a little etc. I also liked this idea as the ultrasonic sensor could maybe be placed a couple of centimetres away. With resistors generating heat, I would assume the resistor has to be placed right at the inlet which is not always possible.

I know another obvious option is a small fan run off a dc motor but that would be noisy and not suitable at night, especially in a bed room.

Any other ideas or thoughts on this topic.

I look forward to feedback.

Thanks

Colin

dougw · Answer

You could check out piezo fans - they are small, low power and quiet.

shabaz · Answer

Hi Colin, I think Murata have a micro blower, which possibly uses piezo tech (not sure). I've not used it, so I don't know if it is almost silent or not, or how well it would work with the dust sensors. Maybe a more novel way could be to employ some swinging pendulum? They are almost silent when energised by a solenoid from memory (I can't be sure, not had any pendulum clock at home for so long!). Maybe put the sensor on the pendulum : )

BigG · Answer

Wow, thanks for all the very helpful suggestions. Yes, an attempt at creating the chimney effect is being deployed using a disposable coffee cup (a novel way of reuse, I suppose). I really like the piezoelectric fan suggestion. Searching online throws up a few good YouTube videos, which really help demonstrate its effectiveness. Of course, the only downside with the COT's option is the very high price. It's time to get creative if I want to do something similar. On the other hand, the Murata microblower is more reasonable. Looking at the spec sheet it may well use piezo as the spec gives a resonant frequency of 24.0 to 27.0 kHz. Will have to explore this option further. Thanks again.

genebren · Answer

The Murata Microblowers might work, but they are neither cheap or trivial to drive. I used the MZB1001T02 parts on a project for a client, which ended up using full H-bridges to provide the 10 to 20 Vpkpk, 24-27KHz waveforms to get these guys pumping. All that for 0.7 L/min for flow and 1.42 kPa of pressure. I have used some tiny fans in an art project ( PiCasso Design Challenge - Kinetic Art Mobile - Post 3 - Will it go round in circles???? ) that provided plenty of air flow. I have a bunch of these: KD0502PEB1-8, 5V, 0.18A 1.0" x 1.0" x 0.27" or YM0901BFB1, 9V, 0.1A, 0.8" x 0.8" x 0.4" that you could have to try out (shipping only) Good luck!

BigG · Answer

Thanks for your suggestion. Yes, I'm not sure using natural air flow would work in all cases. My view is that dust within a room is not uniform and based on observation tends to collect in areas where there is no natural airflow to prevent settlement or air particulate concentrations. So, my thought is that if you want to develop a trigger/alert scenario you need to place a sensor in or near these locations. Nevertheless you have highlighted some great placement positions for a sensor using heat differentials within a room. I really like your observation that heat from human body and of course movement can also be used. This would make sense for placing a dust sensor below a bed, for example. Now, I wondering if it would work with a young child.

dougw · Answer

You could also use a heater and the chimney effect to either suck air past your sensor or push air past the sensor. If you design a 2 stage chimney stack, you could introduce entrained air to reduce the temperature of the air flowing past the sensor.

dubbie · Answer

You could just try to use the natural air flow within a room. The air is never really still within any room unless it is completely closed with no temperature differentials - not realistic. If there is any heating (or cooling) in a room then there will be air flow so you could try a location above (or below - floor level?) a window, or a radiator, near an air conditioning duct or even just the door way to the room, possibly even a light bulb (LED ones still generate some heat). I have even seen the effect of air flow caused by a human body - this was in an art exhibition where there was a large presumably very light weight balloon moving about in the room due only to the presence of people. It was a big room too. So you could look for areas within a room which has consistent temperature differentials and then you will get an air flow. It would need very accurate temperature measurements in order to be able to do this. Dubbie

shabaz · Answer

Wow. I've never seen a fan so tiny or with such a low noise rating. I'm tempted to order it too, just to see it! : ) This reminds me, I opened up a network storage unit last week, and I took a photo of the fan. Reason being, I was impressed with it.. it's been running for more than 8 years, and had finally stopped spinning. I blew the dust off it using a spray can, and now it's running again. I have an alternative replacement fan, but since this one has been so reliable, I felt perhaps I shouldn't change it out yet.. (it's safe, the network storage will auto-shut-down if the fan stops spinning). The spinning disk has 8 years of uptime too! (it has nothing critical on it, so that won't get swapped out yet either).

michaelkellett · Answer

Farnell have a range of tiny fans, 11 of them <= 17mm square. 2856028 is 16mm square and 4mm thick, noise 3dBA, £5.95, looks like a good choice. MK

michaelkellett · Answer

I think anything you use to pump air will collect dust. The heaters may be a bit less affected (ie they'll still work when dusty) but I think the piezo ' fans ' are mechanically tuned so will work less well when dirty.

The tiny rotary fans may well get noisy when dirty but this one is slower and quieter than many.

You could design a heater based pump that was easily washable.

MK

BigG · Answer

I like the " dust off it using a spray can " method. I have a Dell Vostro 400 that is now almost 12 years old and is still being used daily. The fans got rather clogged up with dust and got very noisy. Have to clean with an old toothbrush when the dust gets caked on. They all still working though. I now pat the PC daily as sign of appreciation as its an amazing machine considering the hours its put in. Sadly, it's days are numbered as 32bit windows computing is dying off slowly.

kmikemoo · Answer

While I also like the dusting by spray can method, I have learned to move the item outside before pulling the trigger. No amount of vacuuming seems to be enough to prevent the inevitable dust fog from the initial blasts

kmikemoo · Answer

I know that you said you're opposed to a fan for noise, but an air multiplier with a longer vertical channel could move the noise to floor level. A $5 80mm computer case fan on an online retailer claims 0.08 Sone (around 20dBA?). That would be the equivalent of my furnace or central air unit running. Just a thought... and it could run off of the same wall wart as the rest of your sensor system. It doesn't have to run full out either.

shabaz · Answer

Hehe I was just going to mention that! Going outside is an important part of the process and very easy to miss the first time around, for trigger-happy spray-can users : )

Looking for novel ways to create an air flow for dust or air quality sensor

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