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

BigG

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

  • 0

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

  • 0

    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 : )

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    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.

  • 0

    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!

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    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.

  • 0

    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.

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    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

  • 0 in reply to dubbie

    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.

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    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

  • 0 in reply to michaelkellett

    Thanks MK. I had a quick look on Farnell. It's a nice compact size and the right operating voltage. I see it's quite a "whizzy" little fan with rpm at 6500 rpm, generating a flow rate of 0.012m³/min, which may mean it needs to be quite close to the dust sensor inlet or put inside a funnel. I'm still a little reluctant to use a fan because if my computer fan is anything to go by, it eventually accumulates dust on the blades, making it noisier. But for that price it won't do any harm trying it out.