Data Uplink without Internet connection, APRS-RF, 144.390MHZ

Until now the only way to send station data to the world wide web was through an internet connection provided by a WiFi access point.  Not much of a problem as long as the station is near civilization, and even in somewhat remote areas one could get a wifi hotspot provided by a cellular service, however the monthly service charges can add up pretty quick if all you are doing is running a weather station off of it. Then there are the really remote places, where there simply isn’t any reliable cell service …..

Luckily there is a world wide amateur radio network called APRS  (Automated Packet Reporting System) that among other uses provides a means to distribute weather data. The system operates in the 2 meter HAM band,   144.390 Mhz in the US.   Transmission are picked up by repeaters in strategic locations and eventually are relayed to the Internet for world wide dissemination.  The communication technology  is based on analog modems running at 1200 baud. The system is therefore not blazingly fast, but since a weather station also doesn’t have much to report it is an excellent fit. Being a non commercial solution there is no monthly service cost associated, all you need is the hardware and a HAM license to operate the transmitter.  The license required is the entry level license and is terribly easy to obtain.  The local HAM club probably has a Saturday class where you go in the morning and walk out in the evening with license in hand. ( Actually you have to wait for l the FAA to post your station ID ).

The uploaded data can be observed on one of the APRS internet sites, for example APRS.fi The site provides charts and tables , quite possibly in a better format than WU.

APRS  Weather Station  using Baofeng model UV5R VHF transciver on 144.290 Mhz for uplink.

APRS Weather Station using HAM radio link

To get on the air you will need a handheld  2M HAM transceiver.  I  bough a cheap handheld by Baofeng (UV5RV2+). They run about $30 and are the size of a family radio Walky-Talky.  It’s quite a rugged design and for the price I could not help myself and had to buy two.

The radio needs to be programmed to the correct frequency, the modem and weather station then does the rest.  An external antenna will come in handy to make the most out of the 5 watt transmitter.

To interface between the WX station and the radio I designed a little modem board (Nano Modem) with the help of Mark Qvist who did the initial schematic and firmware (see MicroAPRS )

Tiny modem board that interfaces between  Weather Station and HAM radio to communicate on the APRS network.

APRS Nano Modem interface adapter

The station, modem and radio are wired together at the moment, 3 wires from Station to modem, and  4 from modem to the radio plugs.  If there is a demand, one could make a daughter board that directly plugs onto the station main board to simplify installation.

The station firmware got an upgrade to include the APRS-RF upload option. All that’s needed  is to set the station ID to the operators HAM station identifier and correctly set the long/lat coordinates. The station can report wind,rain,temp, humidity and barometer.

I did some power consumption measurements on the station and modem board.  Since a WiFi connection is not needed in RF mode, the station firmware turns the WiFi module off when not in use. This  significantly reduces the power requirement from 150 ma down to 45ma with passive wind instruments, or 80ma with the active, high resolution sensors.  This is a total of either 0.2 or 0.4 watt total consumption.  — A  small solar setup should be able to handle.

Next up is to build a solar operated station and put it up on a mountain top away from all civilization to see it run in the wild!

G

 

 

WUnderground updated station passwords

If  your station has stopped uploading its data to Weather Underground in recent days then it’s probably do to  the change in WU’s password requirements.

In the past you could use your password that you use to log in on the WU membership page, the place where you register a new station.  Now each station is given a automatically generated key which has to be used in the password field of the station configuration for it to be accepted by the server.   This was done to protect your member-login password from leaking by the non protected (non https) communications of your weather station.

Here is a page at WU  that describes where to find your new station ID keys.

Gary

Running of the grid on solar power

Every now and then I get a request about running the station off the grid. Here are some numbers and calculations to help with figuring out what battery and solar panel is required to get the setup through the winter months in a worst case scenario.

The station including all sensors consumes 0.65W, that is 130mA  at 5V.

Lets assume the station is located in Seattle WA, where the shortest day is a bit more than 8Hrs and consider that we might only get about 50% of the max sun influx during the winter.

During the 16Hrs of night the station will consume 16H * 0.13A = 2AH ,  Using a safety factor of 3 shows us that we should use a battery with a capacitance of at least 6AH.

During the 8Hr day the solar panel needs to provide the current to run the station ( 0.13A) as well as excess current to charge back the battery. Since there is only 8Hrs of light, the 2AH from the day needs to be replenished in 8Hrs, so 2AH/8 =  0.25A.  Together with the running current that totals to 0.38A.  Considering the 50% cloudiness factor from above we double that number to come up with a requirement of about 0.75A from the solar cell.

When looking through Ebay for small solar panels that can stand up to the elements we find the smallest panels come in 10W nominal, for between $20 and $40 a piece.  These panels  have a max current (shortcut) of around 0.7A, ideal for this setup.

For a minimal setup and to eliminate losses in voltage conversion etc I’m using a 6V 12AH sealed led lead acid battery.  To prevent the battery from overcharging in the summer I have a 7.2V shunt regulator across the battery that can handle 10W.  A low-drop-out (LDO) 5V linear regulator provides the regulated power for the station.

An other solution is by using a 12V 15-17AH SLA battery with a 10-20W solar panel. Connect this together with an off the shelf solar charge regulator ( check EBAY, many to choose from for ~$20 ) . Make sure that the charge regulator has one or two  5V USB outputs.  This provides enough power to also run the WiFi hot-spot as well. Run it  at it’s lowest power setting for best performance.

One thing to consider when working in cold climate is that the Battery doesn’t like the cold.  If there is a building put the battery in the warmest place  and insulate it by sticking it into  layers of Styrofoam etc..

An other thing to think about is to build a solar tracker for the panel. There are a few excellent YouTube videos that detail how one can make a tracker with a RC servo and two light sensitive resistors plus a servo tester.  Care must be taken however to not spend more power in tracking than the solution provides.  An Arduino based approach that only adjust once  every 15 minutes and sleeps the rest might be in order.

Gary

 

 

 

 

 

3d Print your own Stevenson Screen !

If you happen to have a 3D printer that needs some exercise you can now print the parts of a radiation shield for the Baro-Hyg sensor yourself.

Phillip Starbuck, a user of the weather station, has  designed two variations of the “upside down dinner plate” variety of Stevenson screen.  Version A incorporates a little fan for forced air aspiration while version B relies on the natural draft.   Both can be mounted on a pipe, or hung from a bracket, or as in my case with a string attached to the eves on the corner of my house.  The string mount so far has prevented any bugs from getting inside and making themselves a home.  I found  that the design works very well, even without a fan.

Check it out for yourself, you find the STL files for your 3D printer on :

http://www.thingiverse.com/thing:1386003

http://www.thingiverse.com/thing:1386333

Pictures to follow.

 

 

 

 

 

NIST Time Server

It has come to my attention that the time server the WiFi station uses by default has stopped accepting calls for the protocol I use.

The station therefore always uses the fallback ( secondary) time server which can lead to initial connection and reporting issues during, or shortly after, bootup of the station.   I recommend to change the  primary server’s IP address from 128.138.140.44 to, for example,  216.228.192.69.  This is done in the station configuration menu under Time.

The boot process of the station can be observed with the Boostrap tool, using the Monitor feature. This allows you to see see if there are problems getting the time.

All weather data services except Weather Underground must have the time set correctly to accept the data.

Gary

AIR_LCDuino

I  finally got back to finish the the Arduino based weather station LCD IMG_20151030_095843display and script.IMG_20151030_102445

The PCB on the left shows the “~uino” board  which has a  rotary knob holds a 8×2 LCD and two LEDs. The Atmega 328P chip is located under the LCD.  The back side  has a 5V regulator and header position for the Air-data sensor (I2C) , the Wind  sensors and the regular Arduino UART interface pins for a 5V FTDI  programming / boot loader connection.

For more display area the 8×2 LCD can be replaced with a larger one  (up to 4×20) and  connected via ribbon so that the  LCD can be mounted separate.

The push button/rotary knob operates the display and setup menu functions.  The same AirData sensor as on the WiFi station is used.

The following items are currently displayed:

– Bus Voltage  (volt)
– Density Altitude (feet)( used in aviation)
– Standard Altitude (feet) (based on Standard Atmosphere)
– Compensated Altitude (feet) (by entering current sea level pressure)
– Station Pressure “hg
– Humidity (%RH)
– Temperature (degF)
– Dew point (degF)  (dry atmosphere)
– Temperature Dewpt. Spread  (used in aviation)
– Wind Direction (deg from North)
– Wind Speed current (Mph)  ( 1 second)
– Wind Average (10 minutes running average)
– Wind Gust ( last 10 minutes )

The two LEDs indicate alarm situations:
– Blue LED comes on when Temp <= 1deg C
– Red LED comes on when Vbus is < 11 or >15 volt
– Red LED comes on when Temp-Dewpt spread is <8 deg F

Wind data is captured and updated once a second, while Baro and Hyg data is done at 2 second interval to prevent self heating of the sensors. At first release all data is displayed in imperial units, there is however plenty program space left to implement metric readout as well, only about 35% of the program memory is used so far.

The housing shown below I machined with a CNC router from a 3/4 thick Walnut plank.  Hardwood flooring makes for cheap and readily available machining stock and the finished cases look really nice.  A certain amount of dust is  involved in the making of it however.

All source files for hardware, software and housing  can be downloaded from GIThub here.

If you have access to a CNC machine that reads g-code, most do,  you can probably cut the case with the .ngc  file provided.

If there is interest  I will build a bunch and have then up for sale.

Send me a note if  interested.

IMG_20151112_134115

Leaking Wind Vane

It has come to my attention that a few wind vanes might develop water leaks which leads to the destruction of the sensor electronics  within.

The water enters along the  shaft at the very top  where it is pressed into the vane itself.  A small scratch in the press fit,  possibly caused by the pressing in of the axle itself  can cause water to wick from the top to the bottom.

To remedy the potential for leakage it is suggested to cover the end of axle where it comes through the plastic with either some UV stable epoxy or with a dab of hot glue.  Also a small drop of thin superglue applied to the top will eliminate the issue.    We are going to use superglue followed by black hot glue for the time being until we figure out what causes the internal scratch in the press-fit.

I also like to stress the point that it is important to wrap the joint where the sensor body and PVC adapter from the wind intersect with electrical tape. Start below the joint and work your way up, overlapping 1/2 of the electrical tape width each turn.

 

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