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Topic: Help with 433mhz receiver (Read 9 times) previous topic - next topic

Agrajag

Ok I'm having trouble trying figure out how to determine where the transmission starts. Here are a bunch of captured transmissions, using long high = 1 and short high = 0. The blue columns add up to the temperature (x10) and the red columns add up to humidity (so first row, temp = 14.6 degrees, humidity = 51%). I'm sure I've got that right because I've checked with different figures over a day now and it's always correct.

The second block was a) when I brought the transmitter inside and b) when I took the battery out/in to see what would change.

111111111111 1100 1110 0101 0000 1001 0010 0011 0011 1010 0001-
        1111 1000 1110 0101 0000 1001 0010 0011 0011 1010 0001---
  1111111111 0100 1110 0101 0000 1001 0010 0011 0011 1010 0001----
11111111111 1100 1110 0101 0000 1001 0010 0011 0011 1010 0001------
        1111 1010 1110 0101 0000 1001 0010 0011 0011 1010 0001---
     1111111 0100 1110 0101 0000 1001 0010 0011 0011 1010 0001---
          11 1000 1110 0101 0000 1001 0010 0011 0100 0011 0110-----
         111 0100 1110 0101 0000 1001 0010 0011 0100 0011 0110----
      111111 0100 1110 0101 0000 1001 0001 0011 0100 0001 1011---
         111 1100 1110 0101 0000 1001 0001 0011 0100 0001 1011------
       11111 1010 1110 0101 0000 1001 0001 0011 0100 0001 1011--
  1111111111 0100 1110 0101 0000 1001 0001 0011 0100 0001 1011--
        1111 1100 1110 0101 0000 1001 0001 0011 0100 0001 1011--
          11 0100 1110 0101 0000 1001 0001 0011 0100 0001 1011------
         111 1010 1110 0101 0000 1001 0001 0011 0100 0001 1011----

111111111111 0100 0111 0110 0000 1001 0010 0011 0100 0110 1100----
     1111111 0100 0111 0110 0000 1001 0010 0011 0100 0110 1100----
       11111 0100 0111 0110 0000 1001 0010 0011 0100 0110 1100---
    11111111 0100 0111 0110 0000 1001 0010 0011 0100 0110 1100-
      111111 0100 0111 0110 0000 1001 0010 0011 0101 0101 1101---------
     1111111 0100 0111 0110 0000 1001 0010 0011 0101 0101 1101----
      111111 0100 0111 0110 0000 1001 0010 0011 0101 0101 1101-
     1111111 0100 0111 0110 0000 1001 0010 0011 0101 0101 1101----
    11111111 0100 0111 0110 0000 1001 0100 0011 0101 0000 0111-----
      111111 0100 0111 0110 0000 1001 0100 0011 0101 0000 0111------
  1111111111 0100 0111 0110 0000 1001 0100 0011 0101 0000 0111-----
     1111111 0100 0111 0110 0000 1001 0100 0011 0101 0000 0111-----
        1111 0100 0111 0110 0000 1001 0101 0011 0110 1010 0000-------
     1111111 0100 0111 0110 0000 1001 0101 0011 0110 1010 0000-----
  1111111111 0100 0111 0110 0000 1001 1000 0011 0111 1101 0001------
        1111 0100 0111 0110 0000 1010 1000 0011 0111 0110 0011------
         111 0100 0111 0110 0000 1010 1001 0011 0111 1001 0111----
         111 1100 0111 0110 0000 1010 1010 0011 0111 1011 1010-
          11 0100 0111 0110 0000 1010 1010 0011 0111 1011 1010--
1111111 1111 0100 0111 0110 0000 1010 1010 0011 0111 1011 1010---


So I can't make out what the first 4 bits are, they change a fair bit especially when the transmitter was outside (maybe took longer for the AGC to do something because of a weaker signal so those get mixed up?). The next 8 seem to be the station id as those are what changed when I took the batteries out. The last 8 bits are probably a checksum? But I'm not too familiar with different checksum techniques, I've tried a couple of things but haven't been able to work that out.

At least I know I'm on the right track because I've got the temp/humidity! But my main problem now is determining where the transmission starts. It doesn't seem to send any sort of start sequence (the preceding 1s are noise/indistinguishable from noise).

Agrajag

using long high = 1 and short high = 0

Oops sorry other way around, long high = 0, short high = 1.

mauried

There should be a a sign bit for the temperature to indicate whether its above or below 0C.
Sometimes also, there is a battery sense bit , to allow the indoor unit to indicate when a sensors battery needs changing.

Agrajag

There should be a a sign bit for the temperature to indicate whether its above or below 0C.

Heh this might be a bit hard for me to find, it very rarely gets to below 0 where I am. I suppose I could put it in my freezer for a short time.. not sure if it would be happy with that though
Sometimes also, there is a battery sense bit , to allow the indoor unit to indicate when a sensors battery needs changing.

I don't think my weather station has this feature - the indoor part doesn't display that anyway.

Finding out how to determine where the start of the transmission is doing my head in at the moment, all other protocols look like they do something like send a few long highs (0s) to start off with but this one doesn't seem to. :~

mauried

Does the Wireless Station support more than 1 wireless sensor.
Does it support other types of sensors like rain or wind.
If so, then there have to be fields in the data transmission to identify sensor ID and sensor type.
Usually at the start, there is a long row of 1-0-1-0-1-0 transitions to
a/ Give the receivers AGC time to adjust to the incoming RF signal.
b/ Provide the receivers data slicer with the halfway point of the 1-0 transitions.

Its normal for the next data field to be static as an indication of the start of the valid data, and its normally a
value with an equal number of 1s and 0s .
You sometimes cant figure out what everything means , as the manufacturers allow room for expansion and put data fields
in the transmissions that currently have no use.

Ultimately, you may have to test your decoding skills, by making yourself a small transmitter using the companion 433 Mhz transmitter module
and hooking it up to a microcontroller programmed to send a data stream , and see if the weather console responds to your transmissions.



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