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record_temperature_from_lexibook_asm30_sensor

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Record temperature from Lexibook ASM30 sensor with Arduino

Needed hardware

  • Arduino Uno R3 board (available on Amazon) with USB cable
  • 433Mhz RF transmitter and receiver (available on eBay)
  • Lexibook ASM30 temperature sensor: I had one since many years and I noticed it communicates with 433RF signals with the base

Assembly

It is very simple. Just connect the RF 433 receiver like this:

  • GND to Arduino pin GND
  • VCC to Arduino pin 5V
  • DATA to Arduino DIGITAL pin 2

Then I suppose you have the Arduino connected with a USB cable to a PC running the Arduino development environment.

Reverse engineering Lexibook ASM30 temperature sensor

I tried RFControl sniffer to see if some signals can be discovered. RFControl outputs pulse timing if the same code is received twice.

The ASM30 sensor sends data every 30 seconds, corresponding to the time when the LED is flashing. And RFControl detects some data exactly at the same time!

Analysing the timings show several things :

  • There is a short timing (<500) each other pulse
  • Some pulse have medium duration (around 1900)
  • Some pulse have long duration (around 4500)
  • The full frame is sent 3 times with a timing >9500 between frames

My asumption was a short pulse was a separator, a medium pulse was a “0” bit and a long pulse a “1” bit. So I tried to decode bytes knowing the expected temperature which is displayed on the sensor itself: so easy, the 3rd byte is the temperature x10.

So now, this is what I found:

  • First byte can vary but I don't know yet what is it. Maybe contains the sensor ID
  • Second byte is always the same: “11110000” (240). Probably not an ID (or I am really lucky!), maybe a separator
  • Third byte is the temperature in °C x10
  • 2 next bits are the channel you can choose on the sensor itself: 1, 2 or 3. This is to be able to know the source of the temperature when you have several sensors.
  • Last 2 bits are always “00”, probably stop bits

References

  • RFControl RF 433MHz sniffer library for Arduino: RFControl

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record_temperature_from_lexibook_asm30_sensor.1459588638.txt.gz · Last modified: 2016/04/02 11:17 by sgripon