Searching \ for '[EE]: RF Rx and Tx modules' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/io/serials.htm?key=rf
Search entire site for: 'RF Rx and Tx modules'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: RF Rx and Tx modules'
2004\04\15@104043 by Edson Brusque

face
flavicon
face
Hello,

    I'm testing some transmiters and receivers modules (315MHz e
434MHz) from Keymark (http://www.keymark.com.tw). Transmiters are TXC1-0315 and
TXC1-0434. Receivers are RXD1-0315 and RXD1-0434.

    What I'm founding strange is that the receivers output random noise
when the transmiter is OFF (or ON with data pin low).

    This is ok? Am I doin something wrong?

    It seens the receiving routine would need to ignore all this noise.
I think it would be complex. Any good documents on this subject I should
read before doing dumb questions?

    I've tried to find something on http://www.piclist.com but it seens to be
offline.

    Obrigado,

    Brusque
--
--
---------------------------------------------------------------------
Edson Brusque                     C.I.Tronics Lighting Designers Ltda
Research and Development                   Blumenau  -  SC  -  Brazil
http://www.suporte.ind.br/ryan/netiqueta.htm     http://www.citronics.com.br
---------------------------------------------------------------------

--
http://www.piclist.com hint: To leave the PICList
spam_OUTpiclist-unsubscribe-requestTakeThisOuTspammitvma.mit.edu

2004\04\15@104705 by Andrew Kilpatrick

flavicon
face
Hi,

I've never used these sort of transceivers, but what I do know is
that when the transmitter is off (or out of range) the receiver is
succeptible to all sorts of other crap that is in the air. This is
my experience using other radio devices. With a strong carrier, the
other signals are much less likely to interfere.

As for the noise in the low state, how long are you staying low?
You should probaly use the high state for marking. This might make
it better too, because the low state will always only be short, and
your UART would help you suppress noise in the way it samples the
bits.



Andrew

On Thu, Apr 15, 2004 at 11:40:17AM -0300, Edson Brusque wrote:
{Quote hidden}

--
http://www.piclist.com hint: To leave the PICList
piclist-unsubscribe-requestspamKILLspammitvma.mit.edu

2004\04\15@171933 by David Duffy

flavicon
face
Edson Brusque wrote:

> Hello,
>
>     I'm testing some transmiters and receivers modules (315MHz e
> 434MHz) from Keymark (http://www.keymark.com.tw). Transmiters are TXC1-0315 and
> TXC1-0434. Receivers are RXD1-0315 and RXD1-0434.
>
>     What I'm founding strange is that the receivers output random noise
> when the transmiter is OFF (or ON with data pin low).
>
>     This is ok? Am I doin something wrong?
>
>     It seens the receiving routine would need to ignore all this noise.
> I think it would be complex. Any good documents on this subject I should
> read before doing dumb questions?


This is perfectly normal with typical receivers. I have a product
at the moment that I use a MC145027 to decode a remote and
drive the PIC with the data. That's only convenient now because
I only need the 1-of-4 button data from a set remote address.
The decoder chip just gives me a "data valid" line and the data.
When I want to decode the address as well I'll have to decode
the data from the receiver module bit by bit. (maybe using int0)
David...

--
http://www.piclist.com hint: To leave the PICList
.....piclist-unsubscribe-requestKILLspamspam.....mitvma.mit.edu

2004\04\15@180422 by Brent Brown

picon face
On 15 Apr 2004 at 11:40, Edson Brusque wrote:
>      I'm testing some transmiters and receivers modules (315MHz e
> 434MHz) from Keymark (http://www.keymark.com.tw). Transmiters are TXC1-0315
> and TXC1-0434. Receivers are RXD1-0315 and RXD1-0434.
>
>      What I'm founding strange is that the receivers output random
>      noise
> when the transmiter is OFF (or ON with data pin low).
>
>      This is ok? Am I doin something wrong?

Yes this is normal. No, you are not doing anything wrong. And yes, there is
lots of info on the PIClist already.

This type of encoded is called OOK (On Off Keying). Carrier on for one logic
state, carrier off for the other. When no carrier is present the receiver AGC
(Automatic Gain Control) ramps up the "volume" trying to "listen" for a signal.
The discriminator circuit that outputs the digital 1's and 0's is usually a simple
comparator, the threshold of which follows the average level of the received
level.

When a constant string of data is being sent AND the received signal to the
noise ratio is high AND the data is fairly well "DC balanced" (even number of
1's and 0's) it all works very nicely. From the above description of the
discriminator and AGC you can probably see what can happen to make
things go wrong.

If the data is not DC balanced the discriminator threshold shifts to the point
where noise starts getting discriminated and the data is corrupted.

If the received signal is weak (or there is no signal) the AGC ramps up and
so noise starts getting discriminated again.

There are obviously response times for the above mentioned circuits. These
should be on the spec sheet for the receiver module you are using, and
likewise it should specify a nominal data rate for best performance.

The problem you are faced with is how to determine the start of a valid data
transmission. The first thing you can do, following a period of no data
transmission, is to send a "preamble". This is a burst of transmission that
gets the receiver AGC and discriminator settled down, locked on, tuned in,
etc. The preamble therefore needs to be DC balanced (eg, 0x55 or 0xAA
characters..check them out in binary) and long enough to suit the receiver
response time. The output of the receiver will be noisy at the start of the
preamble, but should be good by the end of it. Your micro needs to ignore
the preamble.

Next problem...syncing the UART (assuming that is what you are using a
UART for receiving data, and that you are sending data in bytes). There are
lots of other methods, but I'll just mention one. If your first data byte
immediately followed the preamble there is no guarantee the UART was
waiting at the expected time for the start bit. By the end of the preamble the
UART is only seeing a continuous stream of alternating 1's and 0's, and will
most likely be getting a lot of framing errors. The preamble gets the receiver
settled, a Sync character or sequence is needed to get the UART settled. A
suggested Sync sequence to send is 2 bytes of 0x0F (0b00001111). See
how it works? A start bit is a 0, then there are 8 bits of data, and the end bit
is a stop. So the UART sees 0000011111. Do that a couple of times and
there is no way the UART can miss the next Start bit. In some cases four or
5 consecutive 1's or 0's is too long and can upset the discriminator, but for
the case of describing the process I think this is the best value to use.

Then you send the data. Make sure there is an even number of 1's and 0's
as already mentioned, and likewise no long series of consecutive 1's or 0's
that will cause un acceptable DC shift in the discriminator threshold. I'll leave
you to do your own research on how to do it...this email is getting too long.

Then you will need a checksum or CRC, because you need to be able to
detect if the data has been received OK or has been corrupted.

Sorry for such a long winded response...hope it helps a bit (or should that be
byte).

--
Brent Brown, Electronic Design Solutions
16 English Street, Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/txt: 025 334 069
eMail:  EraseMEbrent.brownspam_OUTspamTakeThisOuTclear.net.nz

--
http://www.piclist.com hint: To leave the PICList
piclist-unsubscribe-requestspamspam_OUTmitvma.mit.edu

2004\04\16@025629 by Ake Hedman

flavicon
face
Just a quick jump in: This is the best description I ever seen on this
subject. Just great! Even I undestands now... Thanks.

/Ake

-----Ursprungligt meddelande-----
Fran: pic microcontroller discussion list
[@spam@PICLISTKILLspamspamMITVMA.MIT.EDU]For Brent Brown
Skickat: den 16 april 2004 00:04
Till: KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
Amne: Re: [EE]: RF Rx and Tx modules


On 15 Apr 2004 at 11:40, Edson Brusque wrote:
>      I'm testing some transmiters and receivers modules (315MHz e
> 434MHz) from Keymark (http://www.keymark.com.tw). Transmiters are TXC1-0315
> and TXC1-0434. Receivers are RXD1-0315 and RXD1-0434.
>
>      What I'm founding strange is that the receivers output random
>      noise
> when the transmiter is OFF (or ON with data pin low).
>
>      This is ok? Am I doin something wrong?

Yes this is normal. No, you are not doing anything wrong. And yes, there
is
lots of info on the PIClist already.

This type of encoded is called OOK (On Off Keying). Carrier on for one
logic
state, carrier off for the other. When no carrier is present the
receiver AGC
(Automatic Gain Control) ramps up the "volume" trying to "listen" for a
signal.
The discriminator circuit that outputs the digital 1's and 0's is
usually a simple
comparator, the threshold of which follows the average level of the
received
level.

When a constant string of data is being sent AND the received signal to
the
noise ratio is high AND the data is fairly well "DC balanced" (even
number of
1's and 0's) it all works very nicely. From the above description of the
discriminator and AGC you can probably see what can happen to make
things go wrong.

If the data is not DC balanced the discriminator threshold shifts to the
point
where noise starts getting discriminated and the data is corrupted.

If the received signal is weak (or there is no signal) the AGC ramps up
and
so noise starts getting discriminated again.

There are obviously response times for the above mentioned circuits.
These
should be on the spec sheet for the receiver module you are using, and
likewise it should specify a nominal data rate for best performance.

The problem you are faced with is how to determine the start of a valid
data
transmission. The first thing you can do, following a period of no data
transmission, is to send a "preamble". This is a burst of transmission
that
gets the receiver AGC and discriminator settled down, locked on, tuned
in,
etc. The preamble therefore needs to be DC balanced (eg, 0x55 or 0xAA
characters..check them out in binary) and long enough to suit the
receiver
response time. The output of the receiver will be noisy at the start of
the
preamble, but should be good by the end of it. Your micro needs to
ignore
the preamble.

Next problem...syncing the UART (assuming that is what you are using a
UART for receiving data, and that you are sending data in bytes). There
are
lots of other methods, but I'll just mention one. If your first data
byte
immediately followed the preamble there is no guarantee the UART was
waiting at the expected time for the start bit. By the end of the
preamble the
UART is only seeing a continuous stream of alternating 1's and 0's, and
will
most likely be getting a lot of framing errors. The preamble gets the
receiver
settled, a Sync character or sequence is needed to get the UART settled.
A
suggested Sync sequence to send is 2 bytes of 0x0F (0b00001111). See
how it works? A start bit is a 0, then there are 8 bits of data, and the
end bit
is a stop. So the UART sees 0000011111. Do that a couple of times and
there is no way the UART can miss the next Start bit. In some cases four
or
5 consecutive 1's or 0's is too long and can upset the discriminator,
but for
the case of describing the process I think this is the best value to
use.

Then you send the data. Make sure there is an even number of 1's and 0's
as already mentioned, and likewise no long series of consecutive 1's or
0's
that will cause un acceptable DC shift in the discriminator threshold.
I'll leave
you to do your own research on how to do it...this email is getting too
long.

Then you will need a checksum or CRC, because you need to be able to
detect if the data has been received OK or has been corrupted.

Sorry for such a long winded response...hope it helps a bit (or should
that be
byte).

--
Brent Brown, Electronic Design Solutions
16 English Street, Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/txt: 025 334 069
eMail:  RemoveMEbrent.brownTakeThisOuTspamclear.net.nz

--
http://www.piclist.com hint: To leave the PICList
spamBeGonepiclist-unsubscribe-requestspamBeGonespammitvma.mit.edu

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

More... (looser matching)
- Last day of these posts
- In 2004 , 2005 only
- Today
- New search...