Free WM-918 Vista software, free WMR-918 software, free WMR-968 software, free WX-200 software for Vista and XP

This is the manual for

Ken’s Weather Station

For the Oregon Scientific WM-918, also known as the Radio Shack WX200

For the WMR-918, WMR-928, WMR-968 and compatible units


Click here to download Ken’s Weather Station immediately.  (770K bytes)


A Note from the Author

I wrote this program because I don’t like how other programs display the data.  So if your goals or idiosyncrasies are different from mine then you might not be satisfied with this program.


Other programs allow multiple graphs, but only one sensor per graph.  The philosophy of this program is that if graphs are overlaid then the graphs can be larger.  Clutter is reduced by:

1.     Eliminating sensor plots you have little interest in.

2.     Assigning prominent colors (e.g. thick red) to sensors you are most interested in.

3.     Assigning barely noticeable colors (e.g. thin grey) to sensors you seldom want to see graphed.


The program is offered free.  It comes with no guarantees and not much support.  (You get what you pay for.)  You may email me at kq6qv@aol.com.  I will respond to all inquiries.




System Requirements:

·         Windows 2000, XP, or Vista

·         RAM Usage:  2M to 4M bytes while running (depending on window size)

·         Hard Disk:  770K bytes plus 1 megabyte/year of saved data

·         Com Ports supported: Any serial port with any name, or a USB adapter with software serial port simulation



Screen Shots:











Principal Features:

·         This program is a “gadget”:  a program written to run all the time and do so efficiently.  Simultaneously running other applications is no problem.

·         The panel (window) can be resized, from very small to full-screen, and all displayed items resize automatically.

·         A wind gauge and two graphs can be displayed.

·         The main (upper) graph can show up to 24 parameters simultaneously.  The period of time covered is a selectable number of days.  56 days is the upper limit.  The data points are always at 15-minute intervals.

·         The long term (lower) graph can show only one parameter at a time, but it can show three years or more of data.  For most parameters, it shows the daily highs and lows.

·         Sensor average values are appended to a “Data” file every 15 minutes.  Maximum and minimum sensor data is appended to a “LongTerm” file after 24 hours.

·         Up to 3 extra sensors are supported.

·         Upload to CWOP and APRS.

·         A UIView-compatible APRS file is stored.  (This feature is used by the ham radio community.)

·         Features not included:

§  Upload to Weather Underground.

§  Including user-supplied bitmaps in the panel.



There is no formal installation procedure.  You just download it and run it.  The first time it runs it will prompt you for a few things, like where to put files.  It is not a “registered” program and does not show up in the list of installed programs.


Tryout:  When downloading, you don’t have to save the program to disk.  You can run it directly upon download.  In this case you should leave unchecked the boxes “Save weather data” and “Save configuration”.


If you decide the program is “a keeper”, you should create a folder for it and move it there before it tries to store its configuration.  The program saves its configuration in this folder, so the folder should not be read-only.


The configuration file is reorganized in version 2.00.  If upgrading from version 1, you should write down your configuration settings before trying version 2.


The current version:  2.02


This program has been in constant use since May of 2007.


If you try this version, please send me a note and tell me how it worked for you.  Also, be sure to check here periodically to see if a newer version is available.


The program is not regularly tested on Windows 2000.  If you see a bug that might be specific to Windows 2000, please report it to the author.  Whether the program runs on earlier Windows operating systems is unknown.


Operating Procedures:

·         If you click the Setup button, you can change the program’s appearance.  The right mouse button also offers some options.

·         The Graph 1, Graph 2, Graph 3, and Graph 4 buttons select what the main (upper) graph shows.

·         If you click any color panel on the setup window, it will allow you to change the color.

·         A vertical scaling factor is automatically chosen for each graph plot.  You can override these choices using the max and min boxes on the setup window.  These values specify the parameter values at the top and bottom edges of the graphs.

·         If you click any point in the main or long term graphs, the numerical values are displayed.

·         If you click on the weather text, the program reports how well the radio links are working.

·         Typing an “R” (upper case) will reset the radio reception report data.

·         Typing an “S” will write a Screen Shot to the file ScreenShot.bmp in the same folder as the weather data.

·         The max and min sensor readings displayed on the main panel are reset at midnight.

·         Alarms, notifications, and uploads are discussed below.

·         You should provide the pressure correction. (The correction done by the weather unit is ignored.)


Setting the Pressure Correction:

1.    Enter the station elevation on the setup window.  These might be helpful:

§  Borrow a GPS unit.

§  Google terrain maps have elevation lines.

2.    Check “Display sea level pressure” on the setup window.

3.    The formula for sea level pressure requires a temperature from 12 hours ago.  If the program was not running 12 hours ago, wait until this is true.  (The pressure is displayed with a dot after it when this temperature is missing.)

4.    Find an accurate sea level pressure from nearby.  This is best if done on a good-weather day.  Most airports have weather stations, and http://weather.noaa.gov/index.html summarizes them.

5.    Set the “Pressure correction” on the setup window, adjusting it up or down until the program reports the correct sea level pressure.

6.    It is best if you repeat this procedure on different days and average the corrections.  Over time the sea level pressure should average 1013.25 millibars, or 29.92 inHg.

(If you cannot find your elevation, leave the pressure correction zero and adjust the elevation number until the sea level pressure matches the airport value.)


Implementation Details:


The Main Graph

·         You can change the height of this graph, but it is always positioned at the top of the window above the buttons, and it is always as wide as the window.

·         The order in which the plots are drawn is implied by their order on the setup window, in reverse order.  You can change this order.  Typically the “Outdoor Temp” is drawn last, thus making Outdoor Temp “topmost” on the graph.

·         The program always keeps 56 days worth of data in RAM.  When the program starts, it loads this data from the files.

·         Data points are for 15-minute periods ending at 00, 15, 30, and 45 minutes past the hour per the Windows clock.

·         Data points are an average of the sensor samples over the 15-minute period.  Exceptions are Rain Total, Max Wind Speed, and Min Wind Speed.

·         The Average Wind Speed is the gust speed averaged over the 15-minute period.

·         The Average Wind Direction is a proper geometric average over 15 minutes.  (The gust direction is decomposed into orthogonal components using sine and cosine functions, multiplied by the gust speed, and added to variables called NorthWindSum and EastWindSum.  At the end of 15 minutes, these two sums are applied to an arctangent function, and the variables are zeroed.)

·         The Average Wind Velocity is the “Pythagorean sum” of NorthWindSum and EastWindSum, so it is a velocity, not a speed.  Suppose for a 15-minute period the wind blows from the north at 5 mph for 7.5 minutes and then blows from the south at the same speed for the rest of the period.  The average velocity is zero, and the average speed is 5 mph.  The velocity number is more enlightening as to where your air has come from.

·         The default top and bottom graph limits are as follows:

      Parameter:                                         bottom:                                     top:

o   Outdoor Temperature                   note 1                                     note 1

o   Outdoor Dewpoint Temp             note 1                                     note 1

o   Wind Chill Temperature              note 1                                     note 1

o   Indoor Temperature                      note 1                                     note 1

o   Indoor Dewpoint Temp                note 1                                     note 1

o   Extra Sensor Temperature          note 1                                     note 1

o   Extra Sensor Dewpoint Temp     note 1                                     note 1

o   Outdoor Humidity                          0 %                                         100 %

o   Indoor Humidity                             0 %                                         100 %

o   Extra Sensor Humidity                 0 %                                         100 %

o   Barometric pressure                     -40 millibars  note 2             +40 millibars  note 2

o   Rain Rate                                       0                                              4 inches/hour

o   Rain Total                                       0                                              10 inches

o   Average Wind Speed                   0                                              40 miles/hour

o   Minimum Wind Speed                 0                                              40 miles/hour

o   Maximum Wind Speed                0                                              40 miles/hour

o   Average Wind Velocity                0                                              40 miles/hour

o   Average Wind Direction                                                          360º


Note 1 - Temperature limits are chosen by searching for the highest and lowest values that will appear in the graph.  This search includes all temperature parameters together, but excludes any parameter that has a max or min override specified on the setup window.  These highest and lowest values are then rounded up or down to a multiple of 5.

Note 2 – When displaying sea level pressure, the graph midline is always 1013.25 millibars.  When displaying station pressure, the midline is the 8-week average of the station pressure.


The Long Term Graph

·         This graph is always at the bottom of the window.  You can control its height but not its width.

·         Tentative “Long Term” data is written to disk at the end of every hour.  So if the program is taken down for short periods, little or no long term data is lost.  This tentative data is combined and moved to the Long Term file at midnight.  If the program is not running at midnight, the data will be properly recorded on the following midnight.  (The routine that runs at midnight can handle multiple days and is able to avoid mixing data from different days.  If the program is never allowed to run at midnight then no data is ever provided for the Long Term graph.)

·         The default top and bottom limits of the graph are always the highest and lowest values being plotted.  You can override this using the setup window, but the values you supply will be cleared if you switch parameters.


The Wind Gauge

·         This gauge shows the gust wind direction.

·         The gauge is always at the left edge of the window.  The area for it is always square.  You can specify a size for it, but your request will be ignored if it is too big.

·         The pink “rose pattern” shows the recent gust wind directions.  It covers a period that includes the last 10 minutes of wind samples weighted proportional to the recentness of the sample.  (That is, the program uses a windowing function that is triangular in time.)

·         To make the rose pattern smooth, the sample direction is “smeared” some, up to ±20º.  (That is, the wind sample is added to adjacent directions using a windowing function that is triangular in direction.)

·         The contribution of a wind sample to the rose pattern is proportional to the gust wind speed.

·         The green line indicates where the air at your station has been for the previous few hours (the path it has taken to reach your location).  This line is drawn under the assumption that the whole atmosphere moves as a single block with no mixing.  It also assumes the wind at your location is not distorted by the local terrain.  Since both of these assumptions are generally poor, the green line should not be taken as very accurate.

·         The number in the lower-left corner is the distance from your location to the farthest point on the green line.


The Text Data

·         The two small numbers beside the big number are the highest and lowest samples seen during the day.  These numbers are reset at midnight and also when the program starts up.

·         Pressure:  The number in parenthesis gives the offset from the “average pressure” described below.

·         The Rain Today number is since midnight.

·         The Rain Rate is for the most recent 5 minutes.


Data file formats

·         The recorded data files are text files that can be edited by any common editor.  They have fixed-column integer formats.

·         The integer formats for both the Data and Long Term files are the same:

o   The recorded temperatures are always (T+40)*10, where T is in degrees Celsius.

o   Humidities are H*10, where H is in percent.

o   Barometric pressure is (P-500)*10, where P is the raw station pressure in millibars.  The Pressure correction is not included.

o   Wind speeds are W*10, where W is in meters/second.

o   Wind headings are integer degrees.  The Direction correction is included.

o   Rain is in millimeters.  The value in the “Data” files is the value taken from the weather unit’s memory (the “year to date” value).  The number in the “Long Term” files has the midnight value subtracted from it.

o   Rain Rates are in millimeters/hour.  These values are computed continuously and cover the preceding 5 minutes.

o   The “sc” column is the sample count.  In the Data files it is the number of minutes of data, which normally will be about 15.  During “Daylight Saving Time”, 50 is added to this number.  In the Long Term file “sc” is the number of hours of recording that were included (normally 24).

·         Missing data samples are represented as all minuses.  All nines are also allowed (e.g. 9999).

·         Records are allowed for partial periods.  During loading, the program will combine data from records that pertain to the same 15-minute period, with weighting determined by the sample counts.

·         When the program is taken down properly, it will write a record for the partial period.  This does not happen on some Windows shutdowns, so you should terminate this program before shutting down Windows.


About the data

·         The date/clock value held in the weather unit is ignored.  It does not have to be set.

·         The following weather unit data is not recorded by this program.  Instead these values are computed from other data fetched from the unit:

o   Time and date

o   Time of high and low values

o   High and low temperatures and humidities (either indoor or outdoor)

o   High and low wind speeds and rain rates

o   Dewpoints

o   Wind chills

o   Sea-level pressure or pressure trend

o   Rain totals today or yesterday

o   Rain rate

·         The average wind direction (WM-918) and average wind speed kept by the weather unit are fetched from the unit and displayed in the text data, but are not stored in the files.  Instead the 15-minute averages of wind speed, velocity, and direction are computed from the gust speed.

·         You may reset the “year to date” rain total in the weather unit at any time.  The program looks for these resets and cancels them out when drawing the graphs.

·         The Rain Rate is computed from the Rain Total (the year-to-date value).  The rain rate is computed continuously and always covers the preceding 5 minutes.  (A square windowing function is used.)  It is then treated as any other instantaneous sample.  That is, it can immediately appear in the text or trigger an alarm, and it is averaged over 15 minutes for the Main Graph and the data files.  For WM-918 units the sampling period is generally exactly 5 minutes.  But the WMR-type units transmit about every 47 seconds, and occasionally reports are lost when sensors transmit simultaneously, so the sampling period is never exactly 5 minutes.   The program will search through past reports to find the one closest to 5 minutes ago and will compute the rain rate using that one.

·         When the Sea level pressure box is not checked, the program will show the “station pressure”, which is the raw pressure received from the weather unit plus the Pressure correction from the setup page.  It is plotted relative to the 8-week pressure average.

·         The Dewpoint, Wind Chill, and Sea Level Pressure values displayed by this program are computed from these standard formulas:


o   Tdp = b*G/(a-G)    where    G = a*Tc/(b+T) + ln(RH/100)

            Tdp is the dewpoint in ºC

            T is the measured temperature in ºC

            RH is the relative humidity, expressed as a number in the range 0 to 100




o   Twc = 35.74 + .6215*T – 35.75*Vf + .4275*T*Vf    where Vf = antilog(log(V)*0.16)

            Twc is the wind chill temperature in ºF

            T is the measured temperature in ºF                              

            V is the measured average wind speed in miles/hour


Wind chill is not defined above 50 ºF or for wind speeds below 3 mph.  When those happen, the program will substitute the actual temperature.


o   Psl = Ps*exp(Es/H)    where H = 287.1*T/9.80665

Psl is the sea level pressure in millibars

Ps is the station pressure in millibars (Pressure correction included)

Es is the station elevation in meters

T is the 12-hour average temperature in ºK


The 12-hour average temperature is half the current temperature plus half the temperature from exactly 12 hours ago.  When the 12-hour temperature is not available, the 8-week temperature average will be used instead and a dot will appear after the pressure.


APRS data

The data departs from the APRS specification in some minor ways:

1.    The wind speed is a 15 minute average, not 1 minute.

2.    The wind direction is a 15 minute geometric average, not 1 minute.


The APRS file is a two-line file in the format expected by UIView.  The file is rewritten every 15 minutes.  The file is APRSfile.txt in the same folder as the weather data. 



Click the “Alarms” tab on the setup window to see your notification options.  Up to 46 alarms and 7 notifications can be set simultaneously.  Any of these can ring the bell, play a sound, or call any program.  This screen shot shows some examples:




·         If you left-click a line, a box at the bottom of the window allows specifying the alarm or notification.

·         If you right-click a line it is immediately enabled or disabled.

·         Leaving “program” blank specifies the console beep (ding).

·         If the “program” ends in .WAV then C:\Windows\Media is the default directory.  Otherwise the default directory is that which holds the WeatherStation.exe file.  (Specifying .LNK or .BAT files does not generally work.)

·         Alarms for most parameters are caused by instantaneous weather readings, not 15-minute averages.  Exceptions are:

o   Av. Wind Velocity and Av. Wind Direction are 15 minute averages.  The alarm can happen only at the end of a 15-minute period.

o   The Av. Wind Direction “wraps around”, so both an Above and Below value must be specified.  The Below number can be higher than the Above number, in which case the alarm is for any direction between them.  This alarm is not reported if the average velocity is below 5 MPH.

o   Rain Rate is a 5 minute average.  The alarm can happen instantly (at any time).

·         When calling a program, a parameter is passed.  This parameter will be:

o   Every 15 minutes:  “01N ” followed by the new record that was just appended to the data file.  (Some additional parameters are passed.  You may contact the author for an explanation of these.)

o   Every hour:  “02N ” followed by the new “LongTermDataForToday” record.

o   Midnight:  ‘03N “ followed by the new “LongTerm” record.

o   All other alarms and notifys:  A two-digit alarm number followed by an A (above), a B (below), or an N (Notify).  The alarm number is the same as the list position on the setup window.  So for a high outdoor temperature alarm the parameter would be 01A.

·         Uploads are the responsibility of the called program.  Either you can write this program or you can use the add-on described below.


Add-on programs

Two add-on programs have been written.  You may download and use them free.


o   Alarm.exe  -  This program will send an E-mail or announce the alarm using text-to-speech software.  Also it can call another program, which is similar to what WeatherStation.exe can do except “aboves” and “belows” can be distinguished.  (The E-mail feature assumes the sending system has a MAPI-compliant mail facility.  AOL is not MAPI-compliant.  MS Outlook is.)

o   Upload.exe  -  This program will upload weather data to APRS or CWOP (Citizen’s Weather Observer Program, run by NOAA).  (The reporting period is always 15 minutes.  Extra sensors cannot be reported.  You can specify the server.  If the transfer fails, Upload.exe will retry it once after a 30 second wait.  If you do not have a Ham call-sign, you can apply for a CWOP ID at http://www.findu.com/citizenweather/signup.html  To find your latitude and longitude, go to google.com, click “maps”, type in your address, click “Satellite”, zoom in, right-click your station’s exact location, and select “Directions from here”.


To reduce peak server demand, Upload.exe waits a random amount of time, up to 4 minutes, before uploading the data.  If you try to logoff or shutdown, this wait is ended so that the data can be sent immediately, but this might not always work properly.  If you click the “UP” tray icon, the data is sent immediately.  The “Wait time” box allows you to set this wait period to a fixed value.)


Using Add-ons

1.    Download the program, putting it in the same folder as WeatherStation.exe.

2.    Execute the program.  (When called without parameters, it enters “setup mode”.)

3.    Fill in the necessary information and click “Done”.

4.    In WeatherStation setup, click the “Alarms” tab.

5.    Type the name of the add-on program, specifying it for an alarm’s “program”.


Download Alarm.exe now             (500K bytes)

Download Upload.exe now          (700K bytes)


More Screen Shots


Alarm.exe Setup:



Upload.exe Setup:




Hints for using the WMR-series units

1.    When I first got my WMR-968 I was disappointed with the range of the sensors, especially the Extra Sensors.  Eventually I discovered that my computer was interfering with reception.  I recommend that the base unit be at least 20 or 30 feet from any computer or TV.  The computer will desensitize the base even if its emissions are not exactly 433.5 MHz.  On top of that, you should experiment to see if moving the base a foot one way or another causes any improvement.  (One foot is about a half-wave for 433 MHz and is the typical dimension of the null pattern resulting from reflections.)


Although making the bases unit’s antenna vertical gives it non-directional performance, there might be an orientation that picks up less interference from the computer.  If you find that some oblique angle works better, the antennas for all the sensors should be at this same oblique angle.  (The transmitter’s antenna should be parallel to the base unit antenna’s apparent direction as seen from the transmitter, assuming you could see through obstacles such as walls.)


I presently have the base unit just 15 feet away from my computer.  But I was able to use a hand-held communications receiver (ICOM IC-R10) to find a null spot for the base unit.  If you do not have such good test equipment then your only safe option is to buy a serial cable at least 25 feet long.  A ferrite bead on the serial cable at the base unit is also a good idea.  Do not plug the base unit power cord into the same outlets as the computer.  If you have no other option, consider a power line filter for the base.


2.    The published specification for the range of the THGR122NX Extra Sensor is only 100 feet.  But that number is for daytime and no intervening obstacles.  If the signal has to go through or around an exterior wall then 25 feet is the typical limit of usefulness at night.  What is the point of having four outdoor sensors if they have to be so close together?


The antenna in the Extra Sensor is not very efficient.  Fortunately I am an antenna expert.  I designed a booster that adds 5.5 dB to the antenna’s gain.  You can easily build it.  No modification of the sensor is necessary.  It will double the range of the unit to 200 feet.  If there is an intervening exterior wall, the booster will add 100 feet to whatever range you see now.  I haven’t tried the RT918 wireless repeater.




Your best option is to cannibalize an old TV antenna.  The 0.3-inch diameter aluminum rods are ideal, and there is no other common supply of such material.   Copper wire, 14 or 12 gauge, will also work and might be the quickest way for a tryout.  Copper “refrigerator tubing” is another option.  (Technically elements with noncircular cross-sections will work fine, but there is no dependable way to predict the correct element lengths.)


The booster is called a “Three Element Beam”.  The shorter element is the “director”, and the longer element is the “reflector”.  The booster makes the sensor a directional transmitter and it must be pointed at the base unit.  The director is the front.  The director and reflector must be vertical if the base unit’s antenna is vertical.


Construction notes:

·         The reflector must be 6 inches from the sensor’s antenna, ±½ inch.

·         The director must be 10 inches from the sensor’s antenna, ±½ inch.

·         The sensor’s internal antenna is a coiled up dipole arranged vertically.  It runs along the left edge of the sensor.  The rest of the sensor can be considered transparent to 433 MHz.

·         The lengths of the director and reflector depend on the diameter of the element material.  Find the lengths from the graph below.  Cut them ±1/8 inch.  Do not smash the ends closed.  (If you want to keep insects out, plug them with some insulator.)

·         The rod that connects the director and reflector to the sensor is called the “boom”.  It can be an insulator or a conductor.  If it is a conductor then it must cross the sensor along the sensor’s midpoint and must touch only the midpoints of the director and reflector.

·         If copper wire is used, strip off all insulation.

·         The sensor unit hangs on a “platform” that I bolted to the boom.  The platform is thin plastic 2-inches by 3-inches.  It must not be a conductor. 

·         The antenna should be mounted away from other conductors.  Wood becomes a conductor at 433 MHz when wet, and concrete and soil do not have to be wet.  A conducting surface a few inches behind the reflector is no problem.

·         The booster can be painted to make it less noticeable. 


http://www.hdtvprimer.com/WeatherStation/BoosterDiagram.gif  http://www.hdtvprimer.com/WeatherStation/RadiationPattern.gif


Revision history

Version 1.00             4/28/07 

Noticed but not fixed:

1.    Setting the Main Graph start date does not work.

Version 1.01             11/??/07


1.    The long term graph discarded all data for October, November, and December.

Noticed but not fixed:

1.    The program does not handle the transitions to and from Daylight Savings Time.  (The program assumes all days are 24 hours long.)  This might never be fixed.

Version 1.02             2/13/08


1.    Wind chill was computed using the average velocity.  It now uses the average speed.

New feature:  An APRS file is created.

Version 2.00             5/15/08


1.    Numerous minor bugs.

2.    The Main Graph start date now works.


1.    An Alarm feature and numerous minor features.

2.    The program now works with WMR-918 type units, including the WMR-928 and the WMR-968.  The program can handle up to three extra sensors.

3.    The file data can be all minuses for missing data.

4.    The file data now includes a Daylight Savings Time flag, but the present program does nothing with it.  If a future version of the program graphs DST transitions properly then it will work with data produced by Version 2.00.

Version 2.01             7/19/08


1.    The APRS report period for maximum wind gust is now 5 minutes.


1.    The APRS data for 24-hour rain is deleted, but the 1-hour rain number is always accurate.

2.    A proper Sea Level Pressure is computed.

3.    Alarm.exe is new.

4.    Upload.exe is new.  WeatherStation 2.01 is required.  The author’s weather station is now a registered NOAA station.  His data can be seen at http://www.findu.com/cgi-bin/wxpage.cgi?call=kq6qv&last=72 .

Version 2.02             8/12/09


1.    Barometric pressure in APRSfile

2.    Green line mileage display