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In the Air Design Challenge - Pollen & Allergen Sensing – Post 1 (Pollen Sensor)

tomaja

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In the Air Design Challenge - Pollen & Allergen Sensing

 

image

Figure 1. Bad guy (Ambrosia pollen grain)

 

As I’m still waiting for my challenge kit I’m using the time to consider pollen sensing since that might be the weakest point of my project.

 

Possibilities

At this moment I have two alternatives for pollen sensor: Homemade and commercial one.

Using commercial one would make my project much easier and the focus would be on making some nice apps for desktop and mobile but with homemade sensor most efforts would be on making the sensor do its thing...

 

1) Homemade pollen sensor

As my plan is to detect pollen, I did some research and discovered a paper on pollen sensing that proposes an idea which seems feasible (Shigeto Kawashima et al. - An algorithm and a device for counting airborne pollen automatically using laser optics).

This task would require very much hard work and could easily turn out to be a failure but I can still try. Some optics would be required - hopefully I will be able to obtain all the necessary parts to build the prototype.

image

Figure 2. Pollen sensor

 

Authors propose that red laser should be used but I think that maybe green or yellow laser would be more appropriate because pollen colour is usually the same (i.e. it reflects green or yellow). I bought the green (532nm) one locally to be used for this purpose.

In order to observe the photodiode sensor signals an oscilloscope is required so I decided to order one that fits in the budget (PicoScope 2204A). It arrived in just two days(!) and as I last used the oscilloscope ~15 years ago (at university) I spend some time testing it – It turned out it’s like riding a bike image

 

2) Commercial sensor

Now some bad news regarding the commercial pollen sensor… The one that I found (http://www.shinyei.co.jp/stc/optical/poln/main_poln_e.html) is not suitable for my location.

It only detects Japanese Cedar and Cypress but these pollen particles are bigger than those of Ragweed (which is the most common allergen in this part of Europe). This is not completely bad news as someone in Japan might find this project useful even with this sensor but for me that's probably not good enough.

Ragweed pollen presence in Europe:

image

Figure 3. Ragweed pollen presence in Europe (August 2014)

 

Conclusion

In short, I will most probably focus my work on homemade pollen detection. image

 

 

I will update as soon as my challenge kit arrives (at this moment it’s being held at the local customs)

Comments and suggestions are always welcome.

 

Dragan

Parents

  • Unless you have a good stable workbench, the laser based detector will probably be too much of a challenge.

    You will need to eliminate all vibration and adjust your optics to very tight tolerances.

     

    Take it from me, I used to work with lasers in a laboratory setting and it takes a long time to setup and calibrate the optics.

     

    So I would suggest a commercial unit rather than a DIY sensor.

     

     

    DAB

  • in reply to DAB

    Thanks for your input DAB!

    Well, there are two cons for using the commercial sensor:

         1) Lead time — 3 months

         2) Single sensor price — ~$800

    So, I'm turning to my own sensor + regular dust sensor. This will be a huge effort but if I succeed it will be a huge satisfaction too image

     

    As for the stable workbench, I don't have an active stabilisation but I was hoping to make a sensor which will not be affected by vibration at all (optics should be very simple and shouldn't require too much precision).

  • in reply to shabaz

    Thank you for your kind offer shabaz!

    Yes, Mike is certainly an expert, he helps a lot with his comments and suggestions.

  • in reply to michaelwylie

    Thanks again Mike!

    I was thinking that I should use white LEDs so that I don't have to check what wavelength causes most luminance (because I don't know how could I manage that without proper resources).

     

    As an alternative to white LEDs, I guess I could try with a couple of different monochromatic light sources like laser diodes (one by one) and try to repeat same conditions and measure the light intensity radiated by the pollen grains for each tested source (or try to find some research results on that topic).

    Then I could use the one that caused most luminance and try different PDs to find the peak luminance wavelength. What do you say?

    EDIT: Your link from yesterday provides results I can use for PD selection.

     

    As for the sensor body, I was thinking about using some 3D printing service (I don't have access to 3D printer or CNC machine locally). But I'm still far from having any real design ready, still just thinking about possibilities. One thing I know is that I will somehow have to make the inner surface smooth if I want to use 3D printed body.

     

    I really appreciate your comments, I will have to give special credits to you if this project ends up successful image

     

    Thanks,

    Dragan

  • in reply to tomaja

    I think you should give it a shot, experiment a little like you are planning. Part of the process is learning, so learn and then let us know how it goes. I think if you can get the body done and the optics sorted you'll end up with a response. It might not be a great response, but you'll get something. Unless you've got some friends, machining is usually EXPENSIVE, especially for a single piece. I think you are correct to explore the 3D printing option. The price will depend on the size and tolerance of your sensor body.

     

    Have any friends at the local university or any friends who work with CNC?

  • in reply to michaelwylie

    Thanks, unfortunately no, none of my friends have a CNC access that I'm aware of. (I read your Chinese 3D printer review, I don't have access to even such one image)

    That article you found states that blue light source makes a good choice for excitation. I could buy something like [this] and use the included glasses to make a filter for the detector PD and, as you suggested, avoid that tube bending.

    EDIT: No, I will have to use proper filter, these glasses will filter out the green light too.

  • in reply to tomaja

    You'd need to know what the filter curve for the glasses look like, but it's a really good/inexpensive idea.

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