michaelbell
Posts: 1
Joined: Sun Jun 17, 2018 7:06 pm

433mhz Device unreadable

Sun Jun 17, 2018 7:17 pm

Hello,

Relative raspberrypi newbie here, but I have a background in software development.

I have a receiver and transmitter hooked up to the pi.

It all seems to be working, I have tested with various scripts and I can listen to other devices transmitting in the close vicinity.

Unfortunately the device that I am interested in listening to, is not being detected.
Its this device, and looks to be using the same 434 band.
https://www.soselectronic.com/products/ ... tx-2-50293

Can anyone enlighten me why it isnt showing up?

Thanks

btidey
Posts: 1615
Joined: Sun Feb 17, 2013 6:51 pm

Re: 433mhz Device unreadable

Mon Jun 18, 2018 7:34 am

1) Flat battery, or

2) RX software not set up to recognise the code or modulation this sends, or

3) Broken device, or

4) Something else

So eliminate 1, then tell us how you are trying to recognise device is sending.

mfa298
Posts: 1387
Joined: Tue Apr 22, 2014 11:18 am

Re: 433mhz Device unreadable

Mon Jun 18, 2018 12:56 pm

michaelbell wrote:
Sun Jun 17, 2018 7:17 pm
I have a receiver and transmitter hooked up to the pi.
The cheap tx/rx modules that many people use on their Pi's (and many cheap gadgets use) use a fairly simple form of signal known as OOK (On-Off Keying).
michaelbell wrote:
Sun Jun 17, 2018 7:17 pm
Unfortunately the device that I am interested in listening to, is not being detected.
Its this device, and looks to be using the same 434 band.
https://www.soselectronic.com/products/ ... tx-2-50293
The description for that states:
Keyfob 2-channel AM 433,92MHz Transmitter with KEELOQ HCS301

AM (Amplitude Modulation) is a different modulation scheme (same as is used on your old AM/MW/LW radio receiver). Whilst AM is still relatively simple it's not the same as OOK so you would need a dedicated receiver to pick it up (and dedicated transmitter to send it). Other more complex devices might also use things like FSK to send data.

btidey
Posts: 1615
Joined: Sun Feb 17, 2013 6:51 pm

Re: 433mhz Device unreadable

Mon Jun 18, 2018 2:42 pm

OOK is a subset of AM modulation where the only two amplitude levels are On and Off.

Although it is possible to use multiple levels of amplitude to encode multiple bits per interval, I would be very surprised to see a key fob attempting to do this. I would therefore think that this is actually an OOK device albeit described as AM.

On the other hand if it uses KEELOQ for security then that means the code changes on each use making it harder to decode.

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