HealthCity: The First Probes

We are finally so far in the HealthCity project that we can reveal a bit more about the process and first prototypes. As previously mentioned, our vision with HealthCity is to create a network of devices that can sense different factors across the city of Aarhus, including air pollution (fine particles, gasses etc.), environmental noise, weather conditions, and more. In the beginning, the network will consist of around 50 solar-powered sensing devices. Using wireless communication technologies, each device will continuously report back local conditions to a server - data that will be made publicly available. In the current state, the (limited) live data from the very first sensing probe can already be followed directly from our temporary website, healthcity.io.

Aarhus City Lab

To test the devices we need to have them located in realistic conditions, e.g. close to roads and where people stay. We are currently talking with Aarhus Municipality about the possibility of mounting test devices in their upcoming Aarhus City Lab, which will be a testing facility for digital urban development. The plan is to mount the first 50 units in that area to test the reliability of the system and the incoming data. Read more about the Aarhus City Lab here.

Technical Implementation

The current prototypes are only meant for testing, but we are continuously getting further in determining the combination of sensors that we will be working with in the production versions of the HealthCity devices. Currently, we are implementing the following sensors in the prototypes:

  • Carbon Monoxide (MICS-4514)
  • NO2 (MICS-4514)
  • Particulate Matter (PMS7003)
  • UV (ML8511)
  • Luminosity (TSL2561)
  • Temperature / Pressure / Humidity (BME280)
  • Noise (KY-037)

Besides the various sensors, the devices include

  • Particle Electron for computing and wireless communication
  • 10.000 mAh LiPo 3.7V Battery
  • Solar panels with an approximate output of 9W

So far, the solar charging system performs even better than expected. At the time of writing, the first prototype has been running outside for 22 consecutive days. The initial charge level of the battery was 43 percent, and it is now hovering at 66 percent. Usually, it will lose around 10 percentage points in a night and gain up to 30 percentage points on a sunny (winter) day. On darker days, it will gain less than it loses throughout the night (down to 7 percent), but so far, the brighter days have by far made up for it in the overall calculations - and at 10.000 mAh, the battery can keep the system running without sun for a week or more. Therefore, we foresee that the system in its current configuration can theoretically keep reporting data for an unlimited period of time. The statistics from our first test unit can be followed here.

Furthermore, we are making improvements to the power management from a software perspective as well. As it is now, the frequency in which each unit transmits its sensor values is exclusively determined by the charge level - so if the charge level is high, it will report every 10 minutes, and at very low levels it will report as infrequent as once an hour. However, we are currently working on implementing weather forecasts in this determination. We have developed ForecastEngine, a power management recommendation service that calculates ideal power settings based on local weather forecasts. Consequently, if the charge level is low, but the forecasts estimate that sunlight is coming soon, it will report a bit more often despite the low charge. Alternatively, if the charge level is high, but the forecasts show nothing but rain and thick clouds, it will preserve as much energy as possible, since it is unsure when energy gain is again a possibility. This system secures a more steady stream of data despite changing weather conditions.

The Next Steps

Right now we are finishing the last test prototypes - the goal is to have around five of these in total, each slightly different in size in order to test various solar panel sizes. These five prototypes will all be located at our test facility at Katrinebjerg. Once we establish the final combination of components, we will start working on a more production-ready version with manufactured printed circuit boards, injection molded casing etc., so that we can ramp up production to reach the initial goal of 50 units. Stay tuned for more!