Protocol of the Lacrosse TX3-TH thermo/hygro sensor

Compatible: TX4, et certainly others...

Each frame is 44 bits long. It is composed of:

Example 1
00001010000000001110011100110001011100111101

Example 2
00001010111011001100011000000000011000001100

Example 3
00001010000001000100011100100011011100100111

Example 4
00001010111000001111010100100000010100100101

The active values of the frames are explained below:

Example 1
0000 1010 0000 0000 1110 0111 0011 0001 0111 0011 1101
0 A 0 0 70 7 3 1 7 3 D 
Checksum: (0 + A + 0 + 0 + E + 7 + 3 + 1 + 7 + 3) and F = D D

Example 2
0000 1010 1110 1100 1100 0110 0000 0000 0110 0000 1100
0 A E C 60 6 0 0 6 0 C 
Checksum: (0 + A + E + C + C + 6 + 0 + 0 + 6 + 0) and F = C C

Example 3
0000 1010 0000 0100 0100 0111 0010 0011 0111 0010 0111
0 A 0 4 20 7 2 3 7 2 7 
Checksum: (0 + A + 0 + 4 + 4 + 7 + 2 + 3 + 7 + 2) and F = 7 7

Example 4
0000 1010 1110 0000 1111 0101 0010 0000 0101 0010 0101
0 A E 0 71 5 2 0 5 2 5 
Checksum: (0 + A + E + 0 + F + 5 + 2 + 0 + 5 + 2) and F = 5 5

 Start sequence
 Sensor type
 Sensor Address
 Parity check
 Data values
 Checksum

The measure is on 3 BCD digits, the two first digits are repeated to fill the 5 nibles.

For temperature, an offset of 50 deg has to be substracted from the measure.

  1. [tempe] 23.1 deg
  2. [hygro] 60.0 %
  3. [tempe] 22.3 deg
  4. [hygro] 52.0 %

Thanks to Matthias for the purple bit information.

I am interested by any comment or more information on the format of these frames. Contact: Jean-Paul ROUBELAT - F6FBB

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