I recently bought a Thunderboard Sense board from Silicon Labs. I don't want to repeat all the features (which you can find on the product page), but it provides various environmental sensors (air temperature and humidity, UV and ambient light, air pressure, TVOC for air quality, 6-axis intertial MEMS sensor and a MEMS microphone) connected to an EFR32 wireless SoC. The pre-programmed demo is capable of sending all the measured data from sensor (every 3 seconds I think) over Bluetooth LE to a paired phone (iOS and Android apps available). The mobile application shows kind of a dashboard and let's you see the actual sensor values, check button states and light a few RGB LEDs. A nice feature is also the possibility to stream the data from the mobile app to the Silicon Labs cloud.
Air quality sensor
The kit features a CCS811 air quality sensor and this was the main reason I bought this kit. What a surprise that after powering up the kit (running on CR2032 coin cell), no TVOC / CO2 data was available. Not even the official manual states that in order to measure with this sensor, you need to power it via a USB.
The sensor takes a while to start (approximately 30 seconds) and then displays TVOC level and CO2 level. You can read about TVOC and CO2 relation, after searching for a CO2 sensor. Long story short: the sensors have no CO2 sensitivity at all. The correlation between TVOC level and CO2 levels comes from experiments and do not work if the air is polluted by anything not produced by a human (like cleaning agents, cooking, ...) or generally humidity not caused by breathing (ironing clothes, having a shower...).
Here is an example of a measurement in my home, for about 21 hours (screenshot from the SiLabs cloud):
As you can see, the functions are the same, the only difference is some coefficient that multiplies TVOC level to get CO2 level.
That day, we got up at about 8 AM, opened the windows, closed them at 9 AM and left our home at about 10 AM and returned at about 6 PM (and opened the windows again for 3 hours) and went to sleep at about 10 PM. (We live in a city with ca. 1 million inhabitants, a few kilometers from city center.)
I don't understand what happened after 9 PM, but I experienced a similar pattern in the following day, while working in that room (office work, mainly with a PC). I intentionally left our wardrobes opened for two days.
and a day after that (not present in the room for the whole day, only opened the windows during breakfast and dinner):
I somehow can't imagine I live in so "toxic" environment. Or maybe all the clothes and room equipment really pollutes the air with VOCs. I can't really deduce any statements from these graphs, even knowing what was (or wasn't happening) in the room.
2. Temperature and humidity measurement
One would say that measuring air temperature and humidity is pretty easy, there are so many sensors to choose from, so what could possibly go wrong?
Well..The wireless SoC produces some undesired heat. To be specific, this is what happens after powering up the sensor (15 minutes):
Yes, it raises the temperature of the temperature and humidity sensor with ca. + 5 K, causing the humidity sensor to read ca. - 15 % rH. I also checked the measured values immediately after powering up, before the sensor gets heated, and the values seem to be within +/- 2 % of my favourite SHT31 sensor.
Here is the same in long-term (with easily recognized window-opened time frame):
All this makes this sensor somehow unusable.
3. UV sensor
I don't have graphs to talk over, but I got one practical outcome from this sensor. Even with some heavy clouds, the UV index is not zero. dougw wrote much more about detecting a UV light in his Safe and Sound - Ultraviolet Light Tests - blog 22
Overcast means that the UV index can be half, compared to a sunny day. In reality this means only ca. 5-30 minutes difference between getting a sunburn, depending on your skin phototype. Using a sun lotion is a must for people sensitive to UV light.
4. Silicon Labs cloud
As mentioned above, there is an option to stream the board sensors' data to Silicon Labs cloud and see it via a web browser.
In my experience, the maximum time of streaming a one session is ca. from 22 to 23 hours. This might be an issue of the iOS task scheduler, or implemented on purpose, or a bug. You can only get access to last 10 sessions (all the previous data is lost?) and download the data in CSV format. For some reason, I can't download the data of the newest sessions, so there might be some data limit or another bug (didn't have time to investigate deeper).
The good thing is that the mobile application can be put into background during streaming. However, any Bluetooth disconnection causes the streaming session to stop and has to be restarted manually.
Here is a typical output of a session:
5. iOS mobile app screenshots
Last, I would like to add a few screenshots from the iOS Thunderboard application:
Overall, I have a mixed impression from this board. It features some uncommon sensors, but the readings and interpretation is a completely different story.