Custom Shield - Indoor Air Quality Monitor


The Internet of things has gone big time!


I finally got around having enough bandwidth to undertake this design! I would love a first round of feedback on this.

Feedback on the following will be appreciated:

  1. PCB layout
  2. Sanity checks
  3. Missing features

Here is the link to the repo:


@mohit I must say the design looks great and simple to figure out the schematics!

I’m definitely not the best person to comment this since i only built like 5 simple boards using hand-drawn board designs using a cnc-pcb prototyping. So pardon me for the feedback if it’s weird :smiley:

Some observations:

  1. The MICS5525 datasheet says that the R-load should be >= 820ohms. So would there be an issue to damage the sensor when the user turns the POT till let’s say…0 Ohms…

  2. Will it be better for a hardware debounce for the switches or the software_debounce will eventually be available for use with user switches?

  3. how about a high side mosfet instead of Diode B230. I believe the turn-on resistance is lower and but cost i cant tell…

  4. I remember looking at some circuitry last time which detects when there is USB power coming in from the USB connector and disconnects the main power supply +5v. (If i remember it all correctly)

Cos the user might plug this to use Serial or program over USB and i’m not certain if having the USB port and power supply providing +5v would give an issues :smiley:

  1. The placement of the MICS5525 & TGS2602 might be too close? I was fiddling with a MQ2-sensor yesterday and the heating element does cause the surround air to be rather warm.

I’m not sure how the performance of the individual sensor might be with an external heating beside.

Hope this helps!


The shield looks great @mohit - Thank-you for the nice design :smiley:


Thanks for the inputs Kenneth!

Good point! I think adding a fixed resistor in series would be a good idea.

This could be done in software. I made sure to add the buttons on interrupt pins.

I’m reusing the same switching supply from the Relay Shield so that sourcing will be easier.

The Core has a diode on VIN and should take care of such conditions!

Yeah, I was worried about this. If that has been your observation, I think I’ll play with the placement again.


I’ll look at it again in the morning. Time for bed :slight_smile:


mohit, kennethlimcp, you could use the clickButton library and possibly get away with a single button. :smile:



I looked at the Air Quality Egg design as reference and I’m not sure how they determined how far they would want 2 gas sensors to be apart but it’s a good gauge.


Thanks @kennethlimcp, that was helpful. I moved around a few things and also got rid of the switch mode in place for a linear regulator to reduce any noise. I’ll push the changes EOD.


Interesting YouTube video posted today about Tim Dye who measures air quality as a hobby and as a career. He shows a bunch of different equipment that he uses including an Arduino based device and some particle sensors.


Hi @mohit,
What kind of enclosure did you have in mind for the board ?
Looks like the board is 5.25"W x 1.5"H x ?? in size
and the Grove sensor is 2.33"W x 1.78"H x 0.87"D in size

Im guessing something like

The 1591DTCL looks like it would fit everything.

Im not sure how to fit those in, or even if the grove sensor could be put inside since it sucks air through the sensor.
Is there some kind of standard mounting brackets?

I just wanted a basic case to protect against static and some moisture / drips (in-case its put in a bathroom).


Hi @anthonywebb,
I signed up for airboxlab and they sent me a beta device recently. It has since been renamed Alima “for legal reasons” - I guess copyright.


  • Device looks very nice
  • App looks professional
  • Temperature and humidity readings are accurate


  • Setting up the wi-fi password is ghetto
  • Particulate matter reading doesn’t seem to notice any changes (compared to my Dylos Pro)
  • App doesn’t show any readings much of the time and wont say why.


This is great feedback from beta testers :smiley: heehee


Don’t worry @BDub I gave proper feedback to the CTO and suggested he might try the CC3000, but it doesn’t sound like its going to get much better because its still going to involve :

  1. USB connection to the device
  2. windows app (this currently requires whack-a-mole skills to type in the SSID because it throws you out of the textbox every 10ms)
  3. Drivers
  4. Have you tried turning it off and on again.

I realise its still beta, but its going to need a geek to install it for the foreseeable future.


Article on Indoor Air Quality problems in Aircraft :


@mohit has pointed out that the MICS-5525 has been withdrawn from production this year.
The replacement seems to be the MICS-5524 which is also cheaper. I think that would be the way to go next.
It looks like it is surface mount though - not sure that is a problem ?


Update: A suggested suitable replacement by the supplier was MICS-5526 which is also a surface mount device. The design changes are very straight forward and assembly of the board should not be a concern.

Here is the datasheet:


The MICS-5526 seems to have identical specifications with the MICS-5524 but its twice the price on cdiweb :

MICS-5524 = $5.75
MICS-5526 = $12.50


Did anyone figure out what the difference between the MICS-5526 and MICS-5524 is?

I looked through the datasheets, and can’t find anything but a slight difference in package (although it’s a bit hard to read the package dimensions in the case of the 5524), certainly nothing that would explain the 2x price difference.


Hey guys. I was thinking about building an air-quality monitor just the other day and remembered that one of the custom shields was going to be one. At first it was mentioned that you guys would do a 100-piece run or so of this, not sure if this will still happen, but I’d really like to know! Unfortunately, though, because of the sheer number of parts, I assume this is going to be quite costly, so I’m thinking of building one with a lot less sensors.

I live in a third-world country, in a small town, where a lot of people burn leaves and other general things simply because of their culture. We have regular trash pick-ups almost everyday, but people like to do this, and I despise the smell it leaves all over my house for hours and worry about my health, as this is done on a daily basis by 3 or more neighbours-- I know it sounds whiny, but I can’t stress enough how unpleasant it is.

As I’m getting an AC unit soon, I’ll have one of these set up to warn me to close the windows. Do you guys know what sensor could warn me the fastest? I’m thinking the MiCS-5526/5 will be a safe bet, but I’d appreciate inputs.