wu-upload — Acurite 433 MHz → Weather Underground

Reads a temperature/humidity packet from an Acurite 433 MHz sensor with an RTL-SDR dongle, validates it, and uploads it to a Weather Underground personal weather station.

Also writes a small plain-text file that a local grapher (MRTG, Munin, a cron script — anything that can cat a file) can consume, so one RF read serves both the public upload and local graphing without a second process fighting for the SDR.

Acurite sensor
    -> RTL-SDR / rtl_433
    -> read_acurite.sh
       -> /tmp/lake_temp.txt   (local graphing)
       -> JSON -> wu-upload.sh -> Weather Underground

read_acurite.sh is the only script here that starts rtl_433. Keep it that way: two processes on one dongle will both fail.

Requirements

• An RTL-SDR dongle
• rtl_433 (tested against 23.11)
• jq, stdbuf (coreutils), curl, flock (util-linux), awk
• A Weather Underground PWS station ID and upload key

Files

File	Purpose
read_acurite.sh	Reads one Acurite RF packet; prints it and refreshes the local data file.
wu-upload.sh	Validates a reading and uploads it to Weather Underground.
process_data.sh	No-op compatibility shim for an older cron entry. See below.
secrets.env.example	Template for the upload key file.
crontab.example	Suggested schedule.

Setup

1. Install the scripts. Install the reader first — the uploader looks for it at /usr/local/bin/read_acurite.sh:

   sudo install -m 755 read_acurite.sh /usr/local/bin/read_acurite.sh
   sudo install -m 755 wu-upload.sh    /usr/local/bin/wu-upload.sh

2. Create the secrets file, named after your station ID:

   sudo mkdir -p /etc/pws
   sudo cp secrets.env.example /etc/pws/secrets.env
   sudo chmod 600 /etc/pws/secrets.env
   sudo editor /etc/pws/secrets.env

   wu-upload.sh refuses to run unless this file is mode 600 or 400.

3. Set your station ID. Every setting has an environment override, so no edit to the script is needed:

   STATION_ID=KXXYYYY7 /usr/local/bin/wu-upload.sh

   STATION_ID defaults to the author's own (KCACLEAR4) — override it as above, or edit the defaults at the top of the script. If your reader lives somewhere other than /usr/local/bin/read_acurite.sh, set READER too.

4. Install a schedule — see crontab.example.

read_acurite.sh

Listens on 433.92 MHz and returns as soon as a matching temperature/humidity packet arrives, rather than burning the whole wait window. Defaults to a 90-second window and Acurite sensor ID 460.

# Human-readable
./read_acurite.sh

# JSON, 30-second window
./read_acurite.sh --json 30

Overrides:

Variable	Default	Meaning
ACURITE_ID	460	Sensor ID to accept. Empty accepts any Acurite sensor.
ACURITE_WAIT_SECONDS	90	Read window, also settable as the positional argument.
RTL_FREQ	433.92M	Centre frequency. Set explicitly — the R820T reports "PLL not locked" when left to choose.
LAKE_TEMP_FILE	/tmp/lake_temp.txt	Local data file to refresh.
RTL_433_BIN	autodetected	Path to rtl_433.

Acurite sensor IDs usually change when the battery is replaced. If readings stop, re-run with ACURITE_ID= to discover the new one:

ACURITE_ID= ./read_acurite.sh --json 60

Note that an empty ID will also pick up a neighbour's sensor if one is in range.

The local data file

Every successful read atomically replaces $LAKE_TEMP_FILE (default /tmp/lake_temp.txt). A failed read leaves the last good file in place. The file is mode 644 and holds four lines:

temperature in Fahrenheit
relative humidity percentage
system uptime
hostname

For example:

76.3
49
 10:37:12 up 2 days, 12:14, 2 users, load average: 0.22, 0.17, 0.12
lakeserver

That four-line shape is what MRTG expects from an external script (value 1, value 2, uptime, hostname), so it can be consumed directly by a target such as:

Target[lake]: `cat /tmp/lake_temp.txt`
Options[lake]: nopercent,gauge

Any tool that reads the first two lines will do just as well.

wu-upload.sh

• Takes a non-blocking lock so overlapping runs do not fight over the SDR.
• Calls read_acurite.sh --json with a 60-second window.
• Rejects temperatures outside -40..140 °F and humidity outside 0..100%, rather than publishing obvious sensor faults to a permanent public archive.
• Computes dew point (Magnus-Tetens) and heat index (NWS Rothfusz regression).
• Uploads to Weather Underground.
• Counts consecutive RF misses and escalates from WARN to ERROR after six. A single miss is normal — RF is lossy. Sustained silence is not.
• Logs to $LOGFILE, scrubbing the upload key from any curl output.

Weather Underground returns HTTP 200 for every outcome, so the script checks the response body: success, or INVALIDPASSWORDID meaning the key was rejected.

Environment overrides: STATION_ID, SECRETS, READER, READ_WINDOW, LOGFILE, LOCKFILE, MISSFILE, SOFTWARE, ENDPOINT.

The upload key is read from $SECRETS and is looked up by station, so one secrets file can serve several stations:

WU_UPLOAD_KEY_KCACLEAR4=...
WU_UPLOAD_KEY_KCAOTHER9=...

process_data.sh

A deliberate no-op. An older setup ran a lake-temperature reader from /etc/crontab every five minutes, which launched its own rtl_433 and could compete with the upload job for the SDR. The scheduled upload now obtains the packet and read_acurite.sh refreshes both consumers from that single reading.

The shim exists so a stale /etc/crontab entry does nothing instead of failing. If you have no such entry, you do not need this file.

Troubleshooting

Check the latest values and when they were written:

cat /tmp/lake_temp.txt
stat /tmp/lake_temp.txt

Check uploader status and the current miss streak:

sudo tail -n 50 /var/log/pws/wu-upload.log
cat /run/pws/consecutive-misses

Symptom	Cause
SDR unavailable	Another process claimed the USB device. Confirm no legacy reader is scheduled or running.
No matching Acurite report	Check the battery, widen the read window, or use ACURITE_ID= to find a changed sensor ID.
cannot read /etc/pws/secrets.env	Missing file, or not readable by the user cron runs as.
is mode NNN, want 600	sudo chmod 600 /etc/pws/secrets.env
credentials rejected	Wrong upload key for that station ID.
rtl_433 was not found	Install it, or set RTL_433_BIN.

License

MIT — see LICENSE.