Saturday, November 28, 2015

Acurite 592TXR Temperature and Humidity Sensors now decoded by rtl_433.

I've added decoding of Acurite's 592TXR "Tower" temperature and humidity sensors to rtl_433. These are small, inexpensive, wirelesss (433 Mhz), temperature and humidity sensors. The 592TXR has several different model numbers including 06002RM

These are compatible with Acurite's consoles such as the 01512 that I have as well as Acurite's Acu-Link Internet bridge which posts to acu-link's web page as well as weatherunderground. I picked up the Acurite 5-n-1 Weather Station, a console, and the internet bridge because the support for the 5-n-1 had been added to rtl_433 and the package price was pretty reasonable.

There were a number of people interested in decoding the 592TXR, but for some reason, it never got added, so I finally added it and cleaned up the Acurite 5-n-1 weather station decoding. The pull request got merged November 8th, 2015.

I think the temperature only version, the 592TX, should also be supported but I don't have one to test. Please let me know if it decodes successfully or not.

The protocol used by the Acurite 592TXR and the 5-n-1 weather station are very similar. The weather station's messages are one byte longer, but they are basically the same with the same RF signaling characteristics.

Remotely monitor Refrigerator / Freezer temperature with Acurite 986 and rtl_433 (rtl-sdr)

I suspected the thermostat in my basement refrigerator was going bad, so I picked up an Acurite 986 refrigerator and freezer remote thermometer.  The display unit will give alarms if the temperature goes out of range.

I wanted a better picture of what was going on so I figured out the Acurite's 433 mhz protocol for the 986 sensors. I've added support to rtl_433. The pull request was merged November 20th, 2015.

Now I pump the data into rrdtool and see what's going on. I now see how long and often the compressor is running, and how long it times to warm up between cycles. The spikes are the defrost cycles.

Now I can also monitor/get alerted when I'm out of the house.

I'm pretty happy with the Acurite 986 display and temperature sensors even without the rtl_433 decoding.

Acurite 00986 Refrigerator / Freezer Thermometer Protocol

  • Includes two sensors and a display, labeled 1 and 2, by default Sensor 1 - Refrigerator, 2 - Freezer.
  • Data format: Pulse Position Modulated (PPM), 5 bytes, sent twice, no gap between repeaters
  • Start/sync pulses: two short, with short gaps, followed by 4 long pulse/gaps.
  • Data Format - 5 bytes, sent LSB first, reversed
  • TT - Temperature in Fahrenehit
    • integer, 
    • MSB = sign. Encoding is "Sign and magnitude"
  • II - 16 bit sensor ID changes at each power up
  • SS - status/sensor type
    • 0x01 = Sensor 2 (
    • 0x02 = low battery
  • CC = CRC (CRC-8 polynomial 0x07, little-endian) 
I was able to easily figure out the CRC with CRC RevEng..