Weather Station Prototype

The Weather Station Prototype for Panoptes (described at the Project Panoptes Web Site) is designed to provide enough weather information to make a safe/unsafe decision so that the control system can park the Panoptes hardware in a safe position in case of bad weather.

We are using an Ardunio board (an Arduino Ethernet for the first prototype, and an Ardunio Micro in the current build) as the controller.

The measurements we plan to take are:

• Sky Temperature - We will use the difference between the sky temperature and ambient temperature as a measure of cloudiness. The sky temperature will be measured by an Infrared non-contact thermometer (MLX90614 IR Thermometer). The basic circuit layout and code were adapted from this bildr.org article.
• Ambient Temperature - The ambient temperature will be measured using a DHT22 sensor package which also measures ambient humidity.
• Relative Humidity
• Light Level - We want to detect the ambient light level as a simple day/night indicator. While not critical information for the TCS which can, of course, calculate whether the Sun is in the sky or not, it is easy to add and is useful in case the TCS is shut down for some reason. To do this, we use a TSL230 light meter chip. The basic circuit layout and code were adapted from a bildr.org page similar to what we referenced for the IR thermometer.
• Rain Sensing - A critical safety consideration is the detection of precipitation. We have purchased several Hydreon rain sensors. They are relatively low cost ($50-60) and have no moving parts and should thus be reliable. We are investigating how best to use them as they can be utilized in one of several different modes. The two most critical for us are rain sensor mode and condensation sensing mode in which the device will send a simple electrical signal when rain or moisture is detected. A third device may be utilized in "tipping bucket" mode which measures accumulated rainfall.
• Wind Speed - We will use a simple anemometer for wind speed sensing. The spinning cups of the anemometer are detected by a hall effect sensor which sends one pulse per rotation of the shaft. By counting the time between pulses, one can get a measure of the wind speed.

The weather station's primary task is to make a safe/unsafe condition decision based upon the data it collects. There can be safe/unsafe condition thresholds set based upon the following criterion:

• Cloudiness - If the sky difference temperature (sky minus ambient) becomes low (i.e. the sky is a similar temperature to the ambient), then this indicates that the sky is dense with clouds. If the sky is perfectly clear, then the sky temperature should be much colder than the ambient. Based upon experience with actual conditions at each individual site, a user can set the threshold difference value at which observations should be shut down due to dense cloud cover.
• Humidity - This threshold is designed to avoid condensation on the optics. If the relative humidity is high, observations should be shut down so that the optics (which cool to below ambient when aimed at the cold sky) do not experience dew formation.
• Rain - If the rain sensor detects rain, then observations should be shut down to protect equipment.
• Daylight - In order to avoid the camera being pointed near the Sun which would focus intense heat on the camera's mirror, shutter, or sensor. Operations should be shut down in the case of daylight.
• High Winds - High winds will shake the camera leading to blurred images. The system should be shut down in the case of high winds as useful data is not likely to be obtained under those conditions. In addition, high winds, lead to the risk of blowing dust and debris, so the camera should be parked in a safe orientation to minimize the risk to optics.

The diagram below shows the prototype circuit (used with the Ardunio Ethernet board). It does not include the anemometer, which we did not have at that point, but it does include two analog TMP36 temperature sensors for detecting the temperature inside the electronics box. The current (Nov 1, 2013) PACE software file WeatherStation.ino should run this circuit.