Tempest Weather to APRS Weather String

What This Does

The process is fairly simple.

The PHP script retrieves the most recent station observation,
converts temperature and wind measurements, builds the weather
string, and prints it to standard output.

A cron job redirects that output into a file. BPQ32 then reads
the file through its WXFileName setting.

What You Need

STEP 1

Get Your Tempest API Information

You need two values before the script can retrieve your
weather observations:

WeatherFlow provides Personal Access Tokens for simple
personal integrations such as command-line scripts.

The current WeatherFlow API documentation is available here:

WeatherFlow Tempest API Documentation →

STEP 2

Retrieve the Latest Station Observation

WeatherFlow provides a REST endpoint for retrieving the latest
observation from a station.

The request used by this script follows this form:

https://swd.weatherflow.com/swd/rest/observations/station/STATION_ID?token=ACCESS_TOKEN

In the PHP script, replace:

STEP 3

Create the PHP Script

This is a cleaned-up version of the original command-line
script while preserving the same output format.

I use a filename such as:

<?php

/*
 * Tempest Weather to APRS Weather String
 *
 * Replace the station ID, access token,
 * latitude and longitude with your values.
 */


/* ---------------------------------------------------------
 * Configuration
 * --------------------------------------------------------- */

$station_id = '########';

$access_token =
    'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';


/*
 * APRS position.
 *
 * Change these to the latitude and longitude
 * appropriate for your station.
 */

$latitude  = '3941.42N';
$longitude = '10446.43W';


/* ---------------------------------------------------------
 * Build the Tempest API URL
 * --------------------------------------------------------- */

$url =
    'https://swd.weatherflow.com/swd/rest/' .
    'observations/station/' .
    rawurlencode($station_id) .
    '?token=' .
    rawurlencode($access_token);


/* ---------------------------------------------------------
 * Retrieve the JSON data
 * --------------------------------------------------------- */

$jsondata = @file_get_contents($url);

if ($jsondata === false) {

    fwrite(
        STDERR,
        "ERROR: Unable to retrieve Tempest data.\n"
    );

    exit(1);
}


/* ---------------------------------------------------------
 * Decode JSON
 * --------------------------------------------------------- */

$result = json_decode(
    $jsondata,
    true
);

if (!is_array($result)) {

    fwrite(
        STDERR,
        "ERROR: Invalid JSON returned by Tempest API.\n"
    );

    exit(1);
}


/*
 * Uncomment this while testing if you want
 * to see everything returned by the API.
 */

/*
print_r($result);
*/


/* ---------------------------------------------------------
 * Make sure an observation exists
 * --------------------------------------------------------- */

if (
    !isset($result['obs'][0]) ||
    !is_array($result['obs'][0])
) {

    fwrite(
        STDERR,
        "ERROR: No observation returned.\n"
    );

    exit(1);
}


$obs = $result['obs'][0];


/* ---------------------------------------------------------
 * Convert units
 * --------------------------------------------------------- */

/*
 * Celsius to Fahrenheit
 */

$tempf = round(
    ($obs['air_temperature'] * 1.8) + 32
);


/*
 * Meters/second to miles/hour
 */

$wind_speed = round(
    $obs['wind_avg'] * 2.237
);

$wind_gust = round(
    $obs['wind_gust'] * 2.237
);


/* ---------------------------------------------------------
 * Build the APRS weather string
 * --------------------------------------------------------- */

echo
    "_" .
    $latitude .
    "/" .
    $longitude .
    "_" .
    $obs['wind_direction'] .
    "/" .
    $wind_speed .
    "G" .
    $wind_gust .
    "T" .
    $tempf .
    "P" .
    $obs['precip'] .
    "h" .
    $obs['relative_humidity'] .
    "b" .
    $obs['barometric_pressure'] .
    "\n";

?>

Weather Values Used by the Script

The script uses the following values from the current
Tempest observation:

The original Tempest values for temperature and wind are
converted before they are inserted into my output string.

STEP 4

Test the Script Manually

Before adding cron or BPQ32, make sure the PHP script works
by itself.

Run:

/usr/bin/php /usr/local/bpq32/weatherdecode.php

The script should print one weather string and return to
the command prompt.

STEP 5

Generate the Weather File With cron

Once the script works correctly from the command line,
cron can update the weather file automatically.

My cron entry runs the script every five minutes:

*/5 * * * * /usr/bin/php /usr/local/bpq32/weatherdecode.php > /usr/local/bpq32/current.txt

The > redirects the script output into:

Each run replaces the previous contents with the most recent
weather string.

Check the Generated File

cat /usr/local/bpq32/current.txt

Do this before configuring BPQ32. If the file does not contain
the expected weather data, BPQ32 is not the problem yet.

STEP 6

Configure BPQ32

Once the weather file is being generated correctly, tell
BPQ32 where to find it.

In bpq32.cfg, locate the
WXFileName setting and configure:

WXFileName=/usr/local/bpq32/current.txt

Restart BPQ32 after changing the configuration so that the
updated setting is loaded.

If It Doesn’t Work

A Note About the Access Token

The simple example above keeps the access token directly
in the PHP file because that is how the original script
was written.

If the system has multiple users, the script is stored in
a shared location, or the file may ever be copied to a public
repository, protect the token appropriately.

Configuration Summary