433 MHz RF Receivers: noise-handling

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In attached picture the 2 types of 433MHz receivers I plan to use. Both lack squelch or carrier detect output. And that causes a problem.
If the connected AVR has to respond on every pulse that comes from these receivers, it will be occupied all the time in handling the signal, and rejecting the noisy messages.
To prevent this, I added a filter: this works fine as it blocks all noise with a pulsetime of less than 100 us. Now the AVR still responds on noise, but the good news is that the amount of time spent on this handling is just a few percent of available processing time.
My question to you, fellow freaks, is: what are smarter solutions to solve this problem?

Nard

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What is the data-rate you plan to use ?

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Low. 1200 bits per second probably. Manchester I guess, with CRC or so.

At the moment I am just listening in on what several transmitters produce. Their pulse-trains have bit-times of 600 us.
All I am looking for now, is a smart way to read the bits from the receiver, without spending all available CPU-resources.
At the moment I am testing with the AVR-Analog Comparator with a simular filter, but no hysteresus there. As soon as I have some results I'll post it here.

Nard

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I think its easy to do a vox or squelch in sw (I'm thinking of pcm speech....) look for any sample in a buffer greater than vox threshold, open the vox, set a timer, time out 1 sec after signal loss. You could add a code at the beginning of ea pkt as a channel ID to break squelch.

Imagecraft compiler user

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At 1200 Bits/sec I would think about sampling the
data with 4800Bits/sec (interrupt driven).

Then do some simple preamble-detection, so that if no preamble is detected, not too much computation is needed.

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Thanks guys, you give me something to think about.

Hmmm, I intended to "react" on edges of the incoming data, instead of sampling it. And with edges, noise is a problem.

Much better.

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Plons

Have a look here

http://www.mikrocontroller.net/t...

http://www.mikrocontroller.net/t...

http://www.hoperf.com/pdf/RF12.pdf

These modules are "Cute" ... and 2.5 Eur with "Sammelbestellung" , i just got 30 of those

I guess you know the language :-)

/Bingo

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Don't know if this applies, but I had some help from other freaks here (used with a pair of 4800 bps modules):

Manchester Encoding

The encoding prevents long empty bit field from being transmitted. As you've probably already discovered the receiver is most susceptible to noise when the transmitter is quiet. A 3 or 4 byte preamble sending something like x10101010 is also helpful...

In my setup, the transmitter is sending continuously, so the preamble is sent only once.

(the goofy project itself is here, includes the manch encoding function.)

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Manchester is nice , but hamming might be interesting also where the clock has not got to be derived from the signal

http://michael.dipperstein.com/h...

This would also make sure there is "Bit toggeling" even if sending pure zeroes

/Bingo

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@Bingo600: those are fine modules indeed. But I already have a few, ... not so cute, but still OK. And yeah, I know the language :)
The choice for the coding-method is still open. As said, at the moment I am "listening-in" on existing transmitters. A bit of reverse-engineering.

@dmonn: sure it helps ! ..... as soon as I am that far with these modules ;)

I have some interesting things to sort out. Thanks guys.

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Last Edited: Thu. Dec 29, 2016 - 02:08 PM
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Check out radiohead for protocol drivers, you may find the datagram format will fit your needs.

 

http://www.airspayce.com/mikem/a...

 

 

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Thx -

Last Edited: Thu. Dec 29, 2016 - 02:07 PM
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Smells like SPAM

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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Smells like SPAM

First post, with a product link, on a 9 year old Thread?

 

Oh yea of little faith wink

 

JC 

 

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Sorry Gentlemen. My mistake
I delete this post