The need for speed

Personal Weather Stations (PWS)

Custom high resolution weather station hardware with Rapid-Fire update directly to Weather Underground.

     

Click on the displays above to see charted station details. 

If you do not see any graphic above it's because your browser doesn't do Flash.

Click here to go to see the  local interface of the device instead.

For a full write up of the project go to http://WunderWeatherstation.wordpress.com


WX station sensor tree

My weather stations are designed from the ground up for  high resolution and short interval sensor readings which then are directly fed into the Rapid-Fire Wunderground data ingestion and dissemination  network at a rate down to once every 2 seconds.

The units are self contained, web based and communicate via a WIFI link directly with the internet. This is done without the need for a secondary computer, additional software or separate box. The device runs on less than 5 Watts of power and therefore provides a cost and energy efficient way of reporting weather data in a continuous stream.

Because the device is on a WIFI link the unit can be placed anywhere within the range of your home's WIFI range. The only wiring required is a CAT5 cable to the wind tree. Power is fed to both ends through a junction in this run which can be placed where it is convenient.

The wind sensors are of solid state design using magnetic sensors instead of reed relay switches and potentiometers as found in the commercially available stations.

Wind AnemometerFor the Anemometer, a ball bearing mounted 16 pole magnet housing and a hall effect device is used, giving 8 pulses per revolution instead of a single pulse.  Using the above design makes it possible to have very little rotating mass and virtually no drag or cogging on the rotating cups, which allows the capturing of wind speeds down to  0.5 Mph and the proper measurement of gust and micro gusts in a 15 second capture window. The Anemometer cups are calibrated cups from Davis Instruments.

The wind vane is  based on a magnetic rotary encoder. It producing a pulse width modulated signal that's directly proportional to the direction of magnetic flux over the device. The chosen device has a resolution of 1.4 deg (8 bits) , more than enough for wind direction. The vane is mounted in a roller bearing and also reacts to wind less than 1 Mph. Due to the design calibration of the wind vane is elegantly simple. Instead of having to orient the entire  wind tree on the mast with north one can simply mount the tree in any direction on the roof or a mast, then face the wind vane to north and learn "North" . You can do all of that with a few taps on your Smart Phone standing on the roof using the compass app. The vane itself is from Davis Instruments as well.  

The 3rd device  on the wind tree is a Solar Sensor that measures the radiation during the day. I find this information useful as it indirectly shows cloud cover along with sunrise and sunset.  There is another solar sensor in the works which is a lot smaller and has no angular sensitivity. It can be placed on the wind tree, at the base, or somewhere along the run.  

The Barometer, Temperature and Humidity sensors are on a small separate PCB  a few inches away from the main board, so as not to be potentially affected by heat generated on the main board. If  desired the air data sensor can be moved up to 8 feet away, however the standard configuration is 2-4" below the main board, housed in the base station post. Currently I have two versions of the air data sensor, one using an HP03s barometer and the latest humidity sensor from Honeywell, and the other version is using a Bosch BMP085 barometer and a Sensiron SHT11 humidity device. All of the above sensors are now factory calibrated with correction factors stored in non volatile memory of each sensor. I will probably make a third version using the BOSH and the Honeywell sensors as the Sensiron part is not always available at the vendors I use and is much more expensive and the HP03s barometer is light sensitive.

The main board and it's local sensors (temp/hum/baro/light and possibly rain) are housed in a white hollow post with air holes on the top and bottom. The interior of the post is force aspirated by a fan near the base of the post so that a constant stream of fresh air is flowing over the sensors. The post stands 2 feet tall and looks nice in the yard or next to your house. If desired the post could be made as short as 1 foot or as tall as 4.

The main controller board is designed around a PIC device from Microchip and their tried and tested TCP/IP/WIFI/ stack is used. The wireless access device is by Zero-G (now Microchip) and is FCC approved. The RF module has a built in antenna that in the vertical position is nearly perfectly Omni-directional, for extra range there is an external antenna port that can be used with a rubber ducky antenna or even a high gain yagi if need be.

In addition to the weather station function the main board provides up to 8 digital inputs, 8 digital outputs and 4 analog signal inputs. This could be used for example for alarm or control functions, the exact hardware details have not yet been decided other than that they will be implemented as a daughter board, or in Arduino speak, a Shield.

Since the unit is completely internet based there is no display on the main board to look at and there are no  buttons to press. There is however a USB port and a switch to allow for network configuration of the device via a computer since the configuration of a purely wireless device can be somewhat of a catch 22 otherwise. The USB port, when connected to a computer, becomes a virtual COM device, and during normal operation the station data is also transmitted on that port.  Once configured with the WIFI details, all further configuration can be done via the HTML5 interface using any internet browser. The current station status is displayed and updated at a 1 second interval on the main page of the web interface.

There are no batteries of any kind in the system, so there is nothing to replace in the middle of the winter when the snow is on the roof. Two of the earlier prototype stations have been in continuous operation since 2008 and, except for a flying spider attack on the wind tree, have performed without trouble.

If you have read all the way to here, you no doubt have noticed that I have not mentioned a rain sensor. Well.... the first, and second attempt of making a reliable rain gauge has shown some problems over time. Mostly problems with plugging up the drain or inlet holes with debris, bugs or other green gunk. After experimenting with P-trap/pressure sensor designs I'm going back to a simple teeter-totter device that mounts on-top of the post, or a secondary post.  I think that the rain gauge will need some attention and cleaning now and then and I don't think I want to ever place it on the roof.

Stopping by Home Depot the other day I was ambling along the garden isle when I saw a self emptying tipping bucked rain gauge from AcuRite. The thing was on sale for $19 since is a seasonal item here in CA. I had my doubts as to the "Acu" and "Rite" claim of it but, figured I can't go wrong at that price. Hooked it up and ran a couple of calibrations on it. Not bad for the price, even at the regular $30. It was a little bit off, underreporting by about 20% but a turn on the calibration screws took care of that.  It seemed to be pretty consistent from one run to the other, so I opened up the case and connected a cable to the reed switch inside. I'm sure it's not as precise as a Davis or RainWise bucket with a larger opening,  but it looks nice and has a wireless display to put on your chimney mantel.

Base board , baro, hyg, sol sensor All the components Board inside post Fan inside post