https://github.com/marcelm/clas-ohlson-36-6726

Protocol of the Clas Ohlson 36-6726 wireless thermometer/hygrometer
https://github.com/marcelm/clas-ohlson-36-6726

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Protocol of the Clas Ohlson 36-6726 wireless thermometer/hygrometer

• Host: GitHub
• URL: https://github.com/marcelm/clas-ohlson-36-6726
• Owner: marcelm
• Created: 2019-03-05T23:03:58.000Z (over 7 years ago)
• Default Branch: main
• Last Pushed: 2021-01-26T23:02:39.000Z (over 5 years ago)
• Last Synced: 2025-03-24T04:35:15.380Z (over 1 year ago)
• Language: C++
• Size: 12.7 KB
• Stars: 5
• Watchers: 3
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

          
# Protocol of Clas Ohlson 36-6726 wireless thermometer/hygrometer

The [Clas Ohlson product 36-6726](https://www.clasohlson.com/se/Tr%C3%A5dl%C3%B6s-hygrometer-termometer/36-6726) is an extra temperature/humidity wireless sensor for [Clas Ohlson product 36-6725](https://www.clasohlson.com/se/Tr%C3%A5dl%C3%B6s-hygrometer-termometer/36-6725) and [36-6725-1](https://www.clasohlson.com/se/Tr%C3%A5dl%C3%B6s-hygrometer-termometer/36-6725-1).

The device sends on the usual frequency of 434 MHz. It can be set to one of

three channels via a switch in the battery compartment. It transmits once every

57 seconds when on channel 1, once every ~70 seconds on channel 2, and once

every ~80 seconds on channel 3.

Transmissions use OOK (on-off keying). Each transmission consists of 12

identical copies of the message, with 3.8 ms OFF between messages.

Each message consists of 36 bits, encoded in the following way:

- 0 is transmitted as ~500 µs ON, ~850 µs OFF

- 1 is transmitted as ~500 µs ON, ~1800 µs OFF

In other words: There are 37 ON pulses in each message. The information is encoded in the pauses

between them.

The bits have the following meaning. ("Bit 1" is the bit transmitted first.)

* Bits 1-10: This appears to always be 0101 1011 10.

* Bits 11-12: The channel as set by the switch in the device. 00 is channel 1;

  01 is channel 2; 10 is channel 3.

* Bits 13-24: 10 times temperature in degree celsius, two’s complement (see below)

* Bits 25-28: Seems to always be binary 1111

* Bits 29-36: Humidity (% relative humidity)

The temperature is transmitted as a 12-bit value representing the temperature in

degrees celsius multiplied by 10. For example, 17.9°C is transmitted as

0000 1011 0011 binary, 179 decimal. Negative temperatures are transmitted in

normal two’s complement. That is, -1.3°C is transmitted as 1111 1111 0011

(12-bit two’s complement of 13).

There is possibly a “low battery” bit in the bits described above as being

constant.