Fridge Sensor

The rain gauge receiver's code, described last time was running happily on a ESP8266 + antenna RXB6 when the next challenge came up:

While shopping for a Zigbee receiver (more about it another time), I spotted a fridge sensor Telldus (312716) looking exactly like my F007TH sensors but with a cable and measuring temperature only.

Telldus thermometer for indoor/outdoor


Honestly, the information gathered on different sources about these was totally unclear but I decided to buy one for my chest freezer.

And... obviously, the casing is identical BUT the protocol (F007TP here) is absolutely not compatible with the F007TH. To be clear: they have nothing in common!

Yet, this new sensor was recognised by my RTL-SDR adapter running rtl_433 (but with the wrong temperature -- according to the source code there may be a conflit bitween WH2 & WH5 which are part of the same family).


It appears that the protocol was described more than 10 years ago by Luc Small on his blog, so at least the heavy lifting was done. I only had to use the decoding and CRC calculation in my own code.


As I didn't want to requisition a specific ESP8266 just for one sensor and because it was in the same area as the rain gauge, I decided to merge the decoding functions even if there is very little in common between these 2 applications.

It is unfortunate that the WH2/F007TP protocol doesn't have an easy synchronisation preamble but at least the rain gauge do, so the main loop now checks if there are a number of ~500ns pulses followed by one ~1500ns or if it detects one ~7500ns pulse.

If it's the latter, then it records 64 pulses then calls the rain gauge decoder. If it's the former, then it records 40 pulses then calls the F007TP decoder.

Overall, the routing mechanism is similar to the solution used for 433Mhz remote sockets.


The code is available online (Plateform.IO format this time).

Ecosystem as a diagram

This now brings the ecosystem to: