Custom Shield - Indoor Air Quality Monitor


As I was laying out the mockup of the board today, I realised no matter what we do, if you want to power the board with a 12V supply and down convert it with a linear regulator, there will always be a ton of heat dissipation around the board that may interfere with the readings.

There are two ways in which we can resolve this:

  1. Use a switch mode power supply which will run relatively cooler.
  2. Don’t use the regulator at all and power the board with a 5V wallwart/supply directly.

The second option seems more appealing to me:

  1. Its cheaper
  2. By taking away the power regulator circuit, the board will always run cooler (sans the heat dissipated by the Core) and will be smaller
  3. I can add a power-only USB micro connector in additon to the barrel jack on the board since USB micro chargers are widely available and cheap.

What do you think @Rockvole ?


@mohit, it’s not my call but the USB option opens up so many possibilities like USB power pack, solar/lipo, car adapter and more. :smiley:


@mohit sounds good to me. Actually, I would prefer to only have micro USB for power - wall warts are so easy to find I doubt anyone would bother finding a barrel jack power supply which seem to be typically 9V anyway. So not having a barrel jack is one less way to break something :slight_smile:

Standard USB wall warts are usually 1A I think - is that good enough?

Can you still have all the connectors / lights / buttons etc stick out of one edge - like the first design - its easier for the enclosure.


Hi there,
I’ve been reading this thread in detail since I found it, due to the fact that plenty of the things discussed here are common to my project… so, first of all, thanks so much for all the infos placed here :smile: !

I had my core laying in the drawer for too much time, and in the past days I decided to use it for designing my own weather station, taking “inspiration” from the AirPi project (link)
In fact when I started I wanted to have on the board the basic weather sensors (temp, humidity, pressure, wind and rain) but after seeing how many pins I had unused on the core, I decided to add some air quality sensors, and the AirPi was a good starting point for me, before finding this thread!

I checked also other projects, some of them are listed here (like smartcitizen) and after some tinkering I decided to build my board with the following components:

  • Spark Core (of course!)
  • DHT22 for temperature and humidity measurement
  • BMP180 (breakout board) for pressure (and further temperature)
  • Figaro TGS2600 for Air Contaminants
  • MICS-2710 for NO2
  • MICS-5525 for CO
  • LDR for light
  • 2 RJ11 plugs for wind & rain sensors
  • 3 GROVE style connectors: 1 for extra ADC channel, 1 for I2C and one for serial port (all with GND and VCC)

As you may see, there are a couple of common items :wink: , and seeing that there are some discussion for the aspect of the new board, I though that my comments could be useful to somebody, so this post.

  • DHT22: in my opinion it has to be placed vertically, otherwise its readings will be altered by the PCB heat and - hopefully not - also by the heaters of the nearby sensors.
  • PSU: I totally agree with the 5V supply! if the max voltage on board is 5v, 12v are a total waste. With 5v PSU you can skip the voltage regulators, and have your board powered by a lot of things (powerbanks, USB everything, etc)

A note about the two MICS sensors MICS-2710 & 5525): I searched a lot but it seems that the only place where to find them is at wicked devices (link) but the two of them will cost roughly 75 USD, too much for me.
Thinking also to the future “life” of the board, I think I will have to switch to a SMD component, and a nice option could be the MICS-4514, which houses both sensors in a single package. If I don’t find cheaper suppliers for the TH sensors, I will go with it.

About my project - AirSpark! - I’m finishing defining the schematic in these days: after that I will start a thread in this forum, of course publishing all the project documents. Every comment will be more than welcome!

I hope to have been useful to somebody, in any case thanks for having read all this :smiley:


Interesting project @cerocca - I find the TGS-2602 to be a very good sensor, hopefully I will get a chance to play with the TGS-2600 one day.
I thought about vertical placement of the DHT-22, but I think that leaning it off the edge of the board would keep it away from the PCB and also allow it to be screwed in place (into the enclosure).

The suppliers of the MICS chips don’t make it easy to order their parts so I think its good to find alternatives if possible.


Here is an early mockup:

Changes made:

  1. A USB micro and a screw terminal for power. Removed the power barrel jack.
  2. Unity gain buffer on the MQ and TGS lines
  3. Transistor switch to control the heater coils
  4. Right angled push buttons
  5. Added two extra grove ports - a total of 6 (2 Analog/ 4 Digital)

I figure we can still keep the same RGB LED. We can mount it right angled by bending the leads and using a spacer. This seems like the easiest way to do it without having to use a light pipe.

I’ll start routing this one soon.


I believe that 1Amp would be the minimum requirement. If the user plans to plug in more grove sensors, they may need to provide more. The nice thing about using USB chargers for power is that they are available in a variety of power ratings.


Hi @mohit,
I was really hoping we could put all the USB ports / LEDs / switches along one edge. I don’t think I could put it in an off-the-shelf enclosure otherwise - sorry I’m not trying to cause you extra work.

Very cool on the extra Grove ports - are you able to make 2 ports on the left digital and the other side 2 digital / 2 analog ?
I like the way you put components next to the DHT22 which don’t cause heat.

Good idea turning the LED 90 degrees - makes things much simpler.
The rest looks good to me :smile:


@Rockvole thanks! To be honest I was/am in doubt if using teh TGS2600 or the 2602, in the meanwhile I tried to ask for some samples to Figaro, including a nice socket for their sensors!
I’ll keep the thread updated about that!

For the DHT-22 I agree with you, for this application your placement should work better!
But I don’t like (personal taste) having the component laying out from the board, I’ll tinker more about that.

MICS chip: I’m waiting for a quote for the MICS-4514, let’s see what they tell me .

@mohit very nice layout in the “early mockup”, I’m also planning to have only 1 MQ socket but with transistor control on the heater… by the way, which transistor did you use?
And I don’t see anymore the MICS sensor(s). Or am I wrong?


I took another stab at the layout. This time I’ve put all the buttons, rgb led and power on one side and all the sensor connections on the other. I also changed the potentiometer and the grove connectors to be a right angled.

This makes it easy to plug in/out the sensors without openning the enclosure.


@mohit so the MICS sensors are definetely gone or you plan to include them/it in the final version of the board?


Thanks @mohit - except would you mind making the potentiometers not right angled?
I don’t want users to be able to change those, also it would be good to not have to drill holes in the enclosure for them.

Apart from that I’m happy with everything else.


@cerocca - we decided to simplify the board by not putting sensors on it - only sockets, which reduces manufacturing costs and the chance of sending out faulty boards - plus its easier to test.

There are some nice MICS sensors for sure - it would be possible to put a socket on the board with their SMD package, but the sensors are not pin compatible. Also, it is not easy to obtain their SMD sensors outside the USA - they ignored all of my requests to buy sensors and I am only in Canada.


@Rockvole, from what I can see, it would be easy to create a Grove-compatible MICS sensor board so they can be added off-board. @mohit, should the power for the grove sensors also have transistor control?

@Rockvole, where are you in Canada?! I am in Ottawa! :stuck_out_tongue:


@peekay123 - I agree with you. Later if we find we need an MICS sensor we can make a Grove version and then it also helps the Arduino community - we get to share code and also get to sell more.

I am in Vancouver.


@Rockvole I see. In fact I’m also experiencing some issues in finding the MICS sensors (whatever kind)
I have a couple of enquiries pending, if I get any positive feedback I’ll update the thread.


@mohit - the power screw terminal - can you make it so that it will be internal only (not stick out the enclosure). Is the purpose in-case we need to add a separate power circuit later to provide more amps ? I don’t know if that would be a problem - although the highest amp USB PSU I have seen is 2.1 amps.


Sounds good. I’ll revert back to the upright pots. The screw terminals are a handy way to provide power from sources that don’t terminate in USB connectors. We don’t need to populate it per se, but its nice to have one.

@peekay123 I like the idea of using a switch to power up the grove/mq sensors, but I’m afraid we may introduce unnecessary noise by putting a transistor in series with the sense resistor (Rs). I’ll take a second look at this since it would be nice to save power when operating from a battery source.


Just a thought I had - keep in mind I don’t know what I’m talking about.
What if you had 2 transistors ? And powered the Grove ports separately.

Then theoretically you could lower total amps required by powering up
half the board and then shutting that down and powering up the other half?

I have no idea if that’s a good idea though.


@mohit - I am not objecting to the screw terminals. I thought the use would be either to provide a barrel jack elsewhere on the enclosure. Or perhaps powered from another board which is inside the same enclosure.

If the screws are on top and the holes front to back like :

You could either have no hole in the enclosure and put wires in the lower side and screw wires in internally for power inside the enclosure or a mounted barrel jack. Or if needed you could cut a hole in the enclosure and have the wires screw in the opposite side of the screw terminals to go straight out.