AstroWeatherStation

ESP32 based weather station with features to help operate an astronomical observatory.

GOAL

This project aims to provide all the instructions that are needed to build a weather station for remote astronomical observatories. On top of the usual environmental readings, rain events, cloud coverage and sky quality are reported to allow the safe operation of the observatory.

PRE-REQUISITES (WIP)

BUILD INSTRUCTIONS

• Arduino IDE ( add the lines in bold to ~/.arduino15/packages/espxxxx/hardware/espxxxx/{version}/platform.local.txt )

  • The ALPACA web server uses regular expressions that need to be enabled,

  compiler.cpp.extra_flags=-DASYNCWEBSERVER_REGEX=1

  • A sequential build number is embedded in the code every time a build is made (whether it is successful or not)

  recipe.hooks.prebuild.0.pattern={build.source.path}/../build_seq.sh {build.source.path}

  For the hook to work, you will also need to create a link (or copy the file) to the file "build.sh" from sketch directory to the path of the sketch book. Sorry for the mess ... if you have a better solution, you are most welcome!

STATUS & DEVELOPMENT

This is version 3.0 of the project. The current version is 3.0.0 and has hit production.

New features in this version:

• Hardware

  • Addition of POE module
  • Addition of optional GPS support
  • Addition of an optional I2C UART/GPIO extender (SC16IS750)
  • Two relays to control the observatory dome
  • Input to receive dome status

• Software

  • ASCOM ALPACA Server
  • Support of ultrasonic wind sensors for adverse conditions (frost)
  • Dome closure upon rain event

Improvements:

• Configuration UI
• Removed configuration button and replaced by guard time on the reboot button (10s)
• Clear/cloudy/overcast sky states instead of overcast/clear

The things that might be improved in v3.1 are:

• Software
  • TBD
• Hardware
  • TBD

FEATURES

• Weather parameters:

  • Temperature
  • Pressure
  • Relative humidity
  • Wind speed
  • Wind direction
  • Rain detection
  • Rain intensity

• Astronomical parameters:

  • Cloud coverage
  • Solar irradiance
  • Sky Quality Meter

• Alarms for:

  • Sensor unavailability
  • Rain event
  • Low battery
  • Rain sensor HW problem

• Operations:

  • External reboot button
  • Debug button (to be pushed when rebooting to activate debug mode)
  • External micro USB socket for debugging (serial console) and firmware updates
  • Configuration mode and runtime configuration updates activable via button

SPECIFICATIONS

This section is being reworked as there are different hardware setups.

• Power consumption:
  • Solar panel version:
    • 12mA in sleep mode
    • ~40mA while active (for ~30s)
• Autonomy: N/A (collecting data)
• Measures (from sensor specs)
  • Illuminance range: 0-88k Lux ( up to ~730 W/m² )
  • Temperature range: -40°C to +85°C
  • Pressure: 300 to 1100 hPa
  • Wind speed: 0 to 60 m/s

About the SQM feature

This is now validated.

- 20°FoV lens put in front of the TSL2591 (comparable to the SQM-Lx)
- Calibration against my SQM-LE done

Open points

• The RG9 sensor raises false positives during day because (I guess) of condensation. I try to mitigate this but since it is happening during daytime, it is only a minor issue.

Runtime configuration interface

Alarms format

The station sends alarm to an HTTPS endpoint as a JSON string:

{ "subject": "reason for the alarm", "message": "what happened" }

Data format

The station sends the data to a web server as a JSON string:

{ "battery_level":92, "timestamp":1675767261, "rain_event":0, "temp":16.84000015, "pres":941.1413574, "rh":27.296875, "lux":68181, "ambient":21.42998695, "sky":-3.19000864, "direction":45, "speed":0, "rain":0, "sensors":63 }

Where

• battery_level: in % of 4.2V
• timestamp: Unix epoch time
• rain_event: 1 if awakened by the sensor
• temp: in °C
• pres: in hPa (QFE)
• rh: relative humidity in %
• lux: solar illuminance
• ambient: IR sensor ambient temperature
• sky: IR sensor sky temperature (substract ambient to get sky temperature, if below -20° --> sky is clear)
• direction: wind direction 0=N, 45=NE, 90=E, 135=SE, 180=W, 225=SW, 270=W, 315 NW
• speed: in m/s
• rain: 0=None, 1=Rain drops, 2=Very light, 3=Medium light, 4=Medium, 5=Medium heavy, 6=Heavy, 7=Violent
• sensors: available sensors (see source code)

Tips

• I use female pin headers for the MCU and other boards. I fried a couple of mosfet's during prototyping (even though I have a 15W iron and I am pretty careful) and lost quite some time to troubleshoot the battery level part so I decided to use pin headers too :-)
• I cut the external antenna cable (1m is waaay too long but I could not find a shorter one) and crimped a male SMA to go with the RP-SMA pigtail

REFERENCES

I found inspiration in the following pages / posts:

• No need to push the BOOT button on the ESP32 to upload new sketch
  • https://randomnerdtutorials.com/solved-failed-to-connect-to-esp32-timed-out-waiting-for-packet-header
• Reading battery load level without draining it
  • https://jeelabs.org/2013/05/18/zero-power-measurement-part-2/index.html
• To workaround the 3.3V limitation to trigger the P-FET of the above ( I used an IRF930 to drive the IRF9540 )
  • https://electronics.stackexchange.com/a/562942
• Solar panel tilt
  • https://globalsolaratlas.info/
• TSL2591 response to temperature by Marco Gulino
  • https://github.com/gshau/SQM_TSL2591/commit/9a9ae893cad6f4f078f75384403336409ca85380
• Conversion of lux to W/m²
  • P. Michael, D. Johnston, W. Moreno, 2020. https://pdfs.semanticscholar.org/5d6d/ad2e803382910c8a8b0f2dd0d71e4290051a.pdf, section 5. Conclusions. The bottomline is 120 lx = 1 W/m² is the engineering rule of thumb.