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EMA astronomical meteorological station

The first meteorological station that I installed in the observatory was a team built from the design and plates of Cristobal García, called EMA (acronym of Astronomical Meteorological Station in Spanish) to offer a solution to measure of the main parameters ​​that are needed to control from the point of view meteorological an astronomical observatory.

The station measure:

  • Cloud sensor

  • Rain sensor

  • Night sky quality sensor

  • Temperature, humidity and dew

Additionally you can add:

  • Thermal or weathervane anemometer (I did not install it) 

  • Publiometer


The system consists of two boards, one controller for the sensors and another of 2 relays, one for the opening and closing of the observatory and another for the turning on and off of the condensation control.

Cristobal facilitated the already assembled boards and the part that had to be resolved was the mechanical solution of the assembly and protection of the sensors.

In the photo it can be seen how the control board is installed in a sealed box. In the front of the box an opening has been made and a glass has been glued to allow the passage of the radiation that measures the quality of the night sky, by means of a small board mounted in front of the glass at 45º.


In the upper part of the box, a led is placed for the measurement of the daylight and a board for the detection of humidity by means of very close tracks and some heating resistances for the drying of the board.

In the final assembly, I placed the peltier plate (cloud sensor) in horizontal, and behind the sealed box a plastic container to channel the rainwater to the counting cup.


I installed the temperature sensor next to the sealed box protected from the direct incidence of the sun with stacked dishes bought in a Chinese bazaar.


The assembly is held in a mast with the window facing north and at a height of the ground such that it does not interrupt the visibility of the telescope.

The control board communicates with the PC through RS232, which is converted with adapter to USB. From the control board, a cable communicates with the relay board through which the power supply is provided. The relay board is installed inside the dome to control the opening and closing depending on the detection of unsafe weather.


Cristobal provides the PC software, and the protocol is open to anyone who wants to integrate it into their own software.

Link to the page of Cristobal García:

AAG CloudWatcher weather station

With the evolution of the design of the observatory automation system, I needed to connect the meteorological station to the ACP DC3 Dream software. The EMA was not compatible and I decided to acquire an AAG CloudWatcher, which I installed on the roof closest to the computer, taking advantage of the roof's own inclination, especially so that water does not accumulate in the rain detector.

The photo shows the AAG weather station that includes: cloud, light, temperature and rain detectors. In a second phase I installed an anemometer, given that wind is also a risk factor to be taken into account in the observatory.

You can also see in the picture a GPS that I use for the computer's time synchronization.

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