Deploying Bluetooth Sensors for Urban Measurements of Temperature

 

Yes, it is indeed close to 40 deg C at this location.  Climate change is occurring in Saskatchewan as well.  The photo above shows a commercial Bluetooth-enabled sensor deployed to measure temperature and RH on my porch.  A 3D-printed shelf holds the temperature sensor in place inside of an enclosure.

Over the past year, I've found that there is often a need to measure temperature and Relative Humidity (RH) at different locations in an urban setting.  It is useful to know these variables to make personal choices related to backyard activities.  Moreover, when conducting experiments at home, temperature measurements are useful to characterize electronic circuits or to determine if the tomato plants on my porch require additional water during a warm period.

The sensors were deployed at four different locations.  Since the sensors have Bluetooth transceivers, I can read the temperature using my smartphone.  I can also download data at a distance of approximately 10 m from each sensor.  This mitigates the need to read the temperature and RH on an LCD display, although visual readout is useful to quickly determine these environmental variables without a smartphone.

Another temperature sensor was deployed in my cold storage / pantry downstairs.  The cold storage temperature is usually 10 deg C lower than the ambient outside temperature.  This is useful to know when storing fruit during the winter.

Here is a picture of a temperature sensor installed on a 3D-printed shelf in my garage.  Note the external temperature probe fastened to the wall using zip ties and adhesive cable tie mounts.

Another temperature sensor was installed next to my 3D printer to monitor temperature and RH.  These two variables affect 3D printing.  The plastic filament is hygroscopic and will absorb moisture.  Filament with higher moisture levels tends to become brittle and will jam the printer.

The outdoor deployment of the temperature sensor is useful for measuring cold temperatures.  Here is the sensor measuring temperature during a warmer day in December.

Here is a picture of the temperature sensor box with rime ice formation.

Here is a picture of the temperature sensor enclosure immediately after assembly.

So what do you need for your own deployment?  The parts that I used are listed below.  Some of the parts are not required for all deployments.

  1.  Inkbird IBS-TH1 Plus indoor-outdoor themometer / RH sensor with an external temperature probe. 
  2. Bud Industries PTQ-1108-C enclosure with transparent and hinged lid.  The enclosure is rated for outdoor use. 
  3. Cable gland suitable for ensuring that the external thermometer can be placed outside of the enclosure.
  4. Amphenol LTW vent to ensure that pressure equilibrium occurs between the inside and outside of the enclosure.  This prevents damage to the electronics and also ensures that RH can be roughly estimated.  Moreover, pressure equilibrium ensures that the enclosure case can be manually opened easily without effort.
  5. Mounting screws or double-sided tape for the 3D-printed shelf.
  6. A 3D-printed shelf for a temperature sensor.  Download link: https://github.com/nkinar/Temperature-Sensor-Shelf
  7. Double-sided tape for mounting the sensor.
  8. Zip ties and adhesive cable-tie mounts for wall mounting of the external temperature sensor.
  9. Drill, reamer, and drill bits for creating holes in enclosure cases.
  10. A single AAA battery (Energizer Ultimate Lithium recommended for cold temperatures).  One AAA battery will last approximately a year before replacement.

The 3D-printed shelf was modeled in CAD software and printed on a 3D printer.

Here is a CAD rendering of the 3D-printed shelf.  Note the hole on the side intended for the external temperature sensor cable.  A design version of the shelf with a mounting hole is available for download from the Github site.

The temperature sensors can be accessed over Bluetooth using the Engbird app downloadable from Google Play or the Apple App Store.  The app allows for the temperature to be read remotely and for data to be downloaded from a particular sensor.  You can name the various sensors and plot time series data.

Screenshot of the Engbird app showing the different sensors and the range of temperatures at a location.

Screenshot with a plot of the time series.