STC31 sensor questions

Sensors Environmental
1

I have a couple of questions regarding the STC31 sensor. My application is a weather balloon rising to 100,000 feet.

  1. The data sheet indicates that pressure corrections for the readings (i.e., using setPressure command) by default only work in the range 600-1200 mbar. For ranges outside this, “please contact Sensiron”. How do I compensate for pressures less than 600 mbar? I anticipate the pressure will drop to around 1 mbar.

  2. The examples only show setting the temperature, RH, and pressure during the setup loop. This would be fine if these values stay constant for the duration of the measurements, for example with a stationary detector. It “seems like” I should set these values after each individual measurement since they will change drastically during the balloon flight. Does this sound correct?

  3. related to 2: When a measurement is made, do the STRH3x measurements (temp, RH) get saved automatically? Perhaps I would only need to set the pressure values?

  4. In the library I see a command to EnterSleepMode, but not a corresponding ExitSleepMode. I would like to enter sleep mode after a reading, then exit sleep mode about 2 seconds later to make the next reading. How would I do that?

2

SparkX products are new/experiemental, so providing technical support is tricky/not always possible…but I’ll give it a shot here:

  1. You’d have to ask Sensiron; poke around their website https://sensirion.com/products/support/ and ask them about custom configs

  2. Yes and no…normalizing to those data at ground-level each time should normalize it to the launch location, and that is all the example provides - programming it to recalibrate during flight would be possible…creating code to accomplish this depends on a lot of things…but you can likely find similar examples online

  3. Yes; see https://github.com/sparkfun/SparkFun_ST … _Library.h comment about refresh/staleness

  4. Making another call to get a new measurement should wake the IC back up :smiley:

3

I have recently bought the STC31 sensor and am running it from an Arduino using the Sparkfun library, but I just get really low values for the Co2 %, in the range of -1.4 to -1.5%.

Obviously this should not be a negative number. Can anyone help please?