Hi all,

I want to create a cloud/rain detection system with a MLX90614 infraredsensor. When pointed at a clear sky the temperature read is far below zero celsius. As soon as clouds move in the temperature rises considerable.
I want to create with arduino a utility that sensors a rise in temperature, indicating clouds, and shutting down the observing session. Parking the scope and closing the roof of my ROR.

Has anybody tried this or sees any difficulties?

Regards,

Joshua

Take a look at the WeatherRadio project for a complete project.

Prior to that I used the MLX90614 in a home grown project for the purpose you outlined. Firmata to obtain the sensor data and the existing INDI Weather monitors to decide on warning messages or closing the roof. Attaching As an example, some Arduino Firmata based collection code that sends the data over USB.

 

Thanks, i will look into it.

I use one of these too.  Point of clarification though:

IR is very useful to detect clouds but not rain. If all you want is to close when it's cloudy that will work for sure. What you want is a seasonally-dependent *difference* between air temp and IR sky temp. The actual sky temp varies too much for a single threshold to work.

But the real bugaboo is rain. Failing to close when it's cloudy is no big deal. You just have some bad subs to delete. Failing to close when it's raining can destroy your expensive equipment.  IR doesn't help you here except that closing when its cloudy will usually mean you're still closed when it starts pouring.

But you should also look into a rain sensor in addition to a cloud sensor. These work by either detecting moisture using electrical conductivity of a metal grid (most also include a heater to prevent corrosion after the rain stops), or an optical sensor that actually "sees" the drops on a lens.
 

Yep - what Scott said basically.  I run with a formula from here lunaticoastro.com/aagcw/TechInfo/SkyTemperatureModel.pdf and combine that with a RG15 for rain detection - I then combine that into a web server response that matches the weather watcher requirements fo Ekos can pick up the weather from my weatherstation. 

EG: 
float correct_sky_temp(float Ta, float Ts) {
float Tsky = (K1 / 100) * (Ta - K2 / 10) + (K3/100) * pow(exp(K4/1000*Ta),(K5/100));
Tsky = Ts - Tsky;
if(debug_Td) {
              Serial.print("Ts: ");
              Serial.print(Ts);
              Serial.print(" Ta: ");
              Serial.print(Ta);             
              Serial.print(" Corrected: ");
              Serial.println(Tsky);
             }
             
  return Tsky;
}

I just monitor the max/min sky temperature (saved regularly to persist over power cycles / crashes) and then map that to 0-100% cloud cover:

float cloud_cover = (map(sky_temp*100,cloud_min*100,cloud_max*100,0.00,10000)/100);
 

Hi Joshua,
you might take a look at weatherradio. This is an Arduino-based solution for an entire set of weather related sensors and comes with an INDI integration: github.com/indilib/indi-3rdparty/blob/ma...adme-WeatherRadio.md

Cloud detection with the IR sensor is tricky to get it reliable. With rain detection I‘m currently experimenting. The most promising is the RG-11/RG-15 with optical drop detection.

Thanks all for the usefull info. I keep everybody informed of the progres of the project.