Author Topic: Remote temp. transmitter - which sensor is this?  (Read 834 times)

Lukapple

  • Full Member
  • ***
  • Posts: 155
Remote temp. transmitter - which sensor is this?
« on: February 16, 2019, 06:32:39 AM »
Hi,
I'm trying to fix a remote temperature sensor from a wall clock. Problem is that it shows too high temperature - probably bad temperature sensor?
Can anyone help me to identify which sensor is this (see attached photo).

It would be also great if I could read a signal from that transmitter (433mhz) with Moteino... any idea if that's possible? :)



Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 5935
  • Country: us
    • LowPowerLab
Re: Remote temp. transmitter - which sensor is this?
« Reply #1 on: February 16, 2019, 10:07:15 PM »
Looks like a thermistor. They come in various resistances at a given temperature. Looks like the NTC type are more popular.
Here's a list on DK where you can choose from. How to identify yours I am not sure other than checking resistance at a given temperature and determine from that, maybe there's a better way.

RE transmitter - why bother, just make a Moteino + WeatherShield ;)

Kidding aside - there are actually discussions in the forum about picking up signals from all kinds of such transmitters. I didn't closely follow those threads but I don't believe people have had much luck in actually reading signals from those, but I could be wrong, worth a search.

Lukapple

  • Full Member
  • ***
  • Posts: 155
Re: Remote temp. transmitter - which sensor is this?
« Reply #2 on: February 17, 2019, 06:47:57 AM »
Thanks for the info Felix.
I'll try to figure out which thermistor is used in this case.

RE transmitter - why bother, just make a Moteino + WeatherShield ;)

Kidding aside - there are actually discussions in the forum about picking up signals from all kinds of such transmitters. I didn't closely follow those threads but I don't believe people have had much luck in actually reading signals from those, but I could be wrong, worth a search.
Hehe, I already have Moteino + WeatherShiled  ;D
It would be really cool to somehow find out how are those "Remote temp. transmitter" signals encoded... so I could maybe modify WeatherMote to send signals to Wall Clock  :)

TomWS

  • Hero Member
  • *****
  • Posts: 1888
Re: Remote temp. transmitter - which sensor is this?
« Reply #3 on: February 17, 2019, 08:23:19 AM »
@Lukapple, if you search the forum for OOK library, you may find what you need.  With a Moteino, it certainly is possible to emulate your weather remote and transmit to your wall clock.   I couldn't tell what brand it is from the photos, but the major brands use similar coding and it is documented on the web.

Receiving OOK signals with a Moteino while also using it as a normal Moteino FSK radio is tricky and probably not worth the effort.

Tom

Lukapple

  • Full Member
  • ***
  • Posts: 155
Re: Remote temp. transmitter - which sensor is this?
« Reply #4 on: February 17, 2019, 04:02:31 PM »
@Lukapple, if you search the forum for OOK library, you may find what you need.  With a Moteino, it certainly is possible to emulate your weather remote and transmit to your wall clock.   I couldn't tell what brand it is from the photos, but the major brands use similar coding and it is documented on the web.

Receiving OOK signals with a Moteino while also using it as a normal Moteino FSK radio is tricky and probably not worth the effort.

Tom

Thanks for the hint, I'll do some research on OOK. I know that's probably not worth the effort, but this stuff really interests me and I want to learn something new  :)

The radio controlled wall clock is some XY brand and it looks like this:


And here are some close-up shots of RF transmitter. I can't find any brand info there.
Btw, what is that big black bubble-gum like dot? Is that just LCD controller or is there also controller where all the signal encoding happens?
I'll also try to dissassemble the clock, maybe I'll find out some more stuff from the components in there.







TomWS

  • Hero Member
  • *****
  • Posts: 1888
Re: Remote temp. transmitter - which sensor is this?
« Reply #5 on: February 17, 2019, 08:31:29 PM »
If the clock is working fine, I wouldn't mess with it.  The 'dot' is just epoxy potting compound poured over a humidity sensitive chip (either directly bonded to the PCB or sensitive in its own enclosure).

The key thing, I think, that you'd want to do is look at the data stream from the Weather TX device that you have.  These are definitely NOT sophisticated and probably only consists of two key signals:   Enable (to power up the transmitter) and Data.  The data will be a stream of ones and zeros and then the flipped version of the same data (zeros and ones) so the net energy is half the overall power.  If you look at those bits, compared to the displayed data and the commonly used signals, you can probably find the encoding you need to emulate.  It's actually pretty easy if you have access to a DSO.

Tom

RoSchmi

  • Newbie
  • *
  • Posts: 23
  • Country: de
Re: Remote temp. transmitter - which sensor is this?
« Reply #6 on: February 18, 2019, 10:25:09 AM »
Hi,
some years ago I found a way to receive signals from this kind of transmitter but I used another platform.
On the site you can find a link to a page where somebody used an arduino to read the signals of this kind of transmitter.
I didn't use a RFM69 but used receivers like the  Aurel RX 4MM3. These should work with the Moteino as well.
 https://old.ghielectronics.com/community/codeshare/entry/1060

Lukapple

  • Full Member
  • ***
  • Posts: 155
Re: Remote temp. transmitter - which sensor is this?
« Reply #7 on: February 19, 2019, 04:56:32 AM »
Hi,
first I have to find a way to listen to those RF signals.
So my options are:
- use moteino (or another platform like RoSchmi mentioned, but I prefer Moteino) with OOK library. Does that library also filters signal (remove noise, etc..) or do I need to take care of that?

- use osciloscope. Iíve PoScope and Iím not sure if this kind of analysis can be done with this kind of osciloscope, and what kind of probes should I use (I donít have much experiences with scopes)

- use some RF sniffing tool, which can be expensive. Iíve found this one, which looks promising: RF Exploer

Once I get access to binary data stream, I can start with analysis and try to decode that data.

Lukapple

  • Full Member
  • ***
  • Posts: 155
Re: Remote temp. transmitter - which sensor is this?
« Reply #8 on: February 27, 2019, 04:50:34 PM »
Ok, I'm one step closer to solution. I've captured a signal from temperature transmitter with spectrum analyser tool.
Could someone help me with decoding the signal on attached image.
Temperature was 29.7C and transmitter was set to channel 3 (there is switch with 3 channels).

RoSchmi

  • Newbie
  • *
  • Posts: 23
  • Country: de
Re: Remote temp. transmitter - which sensor is this?
« Reply #9 on: March 02, 2019, 12:28:08 PM »
Hello Lukapple,
please see my last post. The transmitter you showed looks exactly like the transmitter I analyzed. So I think that you can find out from the links on my post and from http://rayshobby.net/reverse-engineer-wireless-temperature-humidity-rain-sensors-part-1/ how the signals can be decoded. I would be interested myself to see how RFM69 can be used to digtitalize the RF-signals.

Lukapple

  • Full Member
  • ***
  • Posts: 155
Re: Remote temp. transmitter - which sensor is this?
« Reply #10 on: March 03, 2019, 02:03:08 PM »
Hello Lukapple,
please see my last post. The transmitter you showed looks exactly like the transmitter I analyzed. So I think that you can find out from the links on my post and from http://rayshobby.net/reverse-engineer-wireless-temperature-humidity-rain-sensors-part-1/ how the signals can be decoded. I would be interested myself to see how RFM69 can be used to digtitalize the RF-signals.

Wow, thanks for the link, good reading! Pattern looks simmilar ... bits are seperated with high signal, 0 is represented with short low signal and 1 with long low. I'll try to decode it and post results. :)

Lukapple

  • Full Member
  • ***
  • Posts: 155
Re: Remote temp. transmitter - which sensor is this?
« Reply #11 on: March 03, 2019, 02:56:31 PM »
Ok, I've figured it out ;D
Temperature in C is hidden here:
0101 10100001 10100001 00101001 00010011  (29.7C,  297 = bin 100101001)

Still gotta figure out what the rest of bits are...
It would be great if I could encode signal from my moteino temperature sensors and send them to this wall clock. But is probably impossible to find out how that checksum is calculated :(

Anyone knows how is this encoding called (low signals of different lenght, separated with high signal)?

edit:
And this is temperature 24.6 (11110110), transmitted on different channels:
01011010 10101100 00001111 01100000 1110 (channel 1)
01011010 10101101 00001111 01100000 1110 (channel 2)
01011010 10101110 00001111 01100000 1110 (channel 3)
I still have no idea what the other bits are... probably crc and battery level (there is low battery indicator on the clock)
« Last Edit: March 03, 2019, 05:47:56 PM by Lukapple »

TomWS

  • Hero Member
  • *****
  • Posts: 1888
Re: Remote temp. transmitter - which sensor is this?
« Reply #12 on: March 03, 2019, 06:22:01 PM »
CRC can't be included in the other bits if the other bits aren't changing as you change the channel encoding.

Occam's Razor says "Just copy the rest of the bits and try it!"  Synthesize different temperatures in the string and see if the clock reflects those temps.

RoSchmi

  • Newbie
  • *
  • Posts: 23
  • Country: de
Re: Remote temp. transmitter - which sensor is this?
« Reply #13 on: March 03, 2019, 06:35:46 PM »
You could try to use nearly empty batteries to see which bits represent the battery level. Some transmitters of this kind set a random ID when they are powered up by changing the batteries.

Lukapple

  • Full Member
  • ***
  • Posts: 155
Re: Remote temp. transmitter - which sensor is this?
« Reply #14 on: March 05, 2019, 03:56:48 AM »
Iíve done another test and put temperature transmitter into freezer. Now I can clearly see which bits are reserved for temperature:
01010100 00101000 11111111 10100000 1110 (-0.6 C)
01010100 00101000 11111111 00100000 1110 (-1.4 C)

I still need to do that test with nearly empty batteries (currently I donít have any :) )

Yes, it looks like CRC isnít included. Iíll just try to copy other bits.

Any idea how to replicate that kind of signal with Moteino(RF69HW)?