Multiple wireless data on same freq.
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Hi All,
I want to be able to use the same frequency to transmit serial data from
wireless RF sensors. Currently I have a WWVB linked system broadcasting the
time on 433mHz, and I have a SHT11 based temp. and humidity sensor
transmitting on 315mHz. I want to run the SHT11 on 433mHz as well, because
that way one receiver in the weather station I am building can get both data
sets.
So, I have been trying with the WAIT modifier, and even with three
characters to recognize, I am still getting a lot of false readings. Is it
possible to do this reliably?
Jonathan
www.madlabs.info
I want to be able to use the same frequency to transmit serial data from
wireless RF sensors. Currently I have a WWVB linked system broadcasting the
time on 433mHz, and I have a SHT11 based temp. and humidity sensor
transmitting on 315mHz. I want to run the SHT11 on 433mHz as well, because
that way one receiver in the weather station I am building can get both data
sets.
So, I have been trying with the WAIT modifier, and even with three
characters to recognize, I am still getting a lot of false readings. Is it
possible to do this reliably?
Jonathan
www.madlabs.info
Comments
>Hi All,
>
>I want to be able to use the same frequency to transmit serial data from
>wireless RF sensors. Currently I have a WWVB linked system broadcasting the
>time on 433mHz, and I have a SHT11 based temp. and humidity sensor
>transmitting on 315mHz. I want to run the SHT11 on 433mHz as well, because
>that way one receiver in the weather station I am building can get both data
>sets.
>
>So, I have been trying with the WAIT modifier, and even with three
>characters to recognize, I am still getting a lot of false readings. Is it
>possible to do this reliably?
>
>Jonathan
>
>www.madlabs.info
Use the master Stamp to poll each of the remotes in turn. Don't try to have
the remotes transmit randomly. If they have nothing to send then they can
say just that. A round robin kind of deal.
Bruce
> Use the master Stamp to poll each of the remotes in turn. Don't try to
have
> the remotes transmit randomly. If they have nothing to send then they can
> say just that. A round robin kind of deal.
I don't think I understand what you are saying. Perhaps I didn't explain the
set up well enough.
The time and date are being constantly broadcast. I need to do this, as at
least one of my applications is very time critical (a seismograph). The
temp. and humidity reading are of course low priority, and don't need to be
updated very often, perhaps once a minute or so.
Do you mean I should have two way communication with the time/temp systems?
Jonathan
www.madlabs.info
>Bruce,
>
>
> > Use the master Stamp to poll each of the remotes in turn. Don't try to
>have
> > the remotes transmit randomly. If they have nothing to send then they can
> > say just that. A round robin kind of deal.
>
>I don't think I understand what you are saying. Perhaps I didn't explain the
>set up well enough.
>
>The time and date are being constantly broadcast. I need to do this, as at
>least one of my applications is very time critical (a seismograph). The
>temp. and humidity reading are of course low priority, and don't need to be
>updated very often, perhaps once a minute or so.
>
>Do you mean I should have two way communication with the time/temp systems?
In one word, yes. Master Stamps sends an addressed inquiry, and only the
addressed
unit responds. It MUST respond, else you know there is a dead unit. If it has
no data, it just sends NADA (or something) otherwise it sends the
appropriate data. If all the remotes were permitted to broadcast at or near
the same time, on the same frequency, you'd have a bunch of jumbled data.
Sound familiar :-)
One alternative might be to use spread spectrum (cell phone) technology.
Many units can then coexist at, near, or on the same frequency. I'm just
not sure what the FCC might have to say about that. OTOH if it were done
with SMS messaging, what could they say :-)
>Jonathan
>
>www.madlabs.info
Bruce
Sounds like I best stick to different frequencies. I would have to add an
transmitter to every project using the time base, which is currently 3 and
growing.
I suppose I could add the Temp/humid sesor to the time keeping system, and
have it transmit both data sets. Then I would lose the portability of the
sensor, which would be a shame. It's nice to be able to move it around and
check out different spots.
Thanks for the help!
Jonathan
www.madlabs.info
Original Message
From: "Bruce Bates" <bvbates@u...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, November 17, 2003 9:38 AM
Subject: Re: [noparse][[/noparse]basicstamps] Multiple wireless data on same freq.
> At 09:31 AM 11/17/03 -0800, Jonathan Peakall wrote:
> >Bruce,
> >
> >
> > > Use the master Stamp to poll each of the remotes in turn. Don't try to
> >have
> > > the remotes transmit randomly. If they have nothing to send then they
can
> > > say just that. A round robin kind of deal.
> >
> >I don't think I understand what you are saying. Perhaps I didn't explain
the
> >set up well enough.
> >
> >The time and date are being constantly broadcast. I need to do this, as
at
> >least one of my applications is very time critical (a seismograph). The
> >temp. and humidity reading are of course low priority, and don't need to
be
> >updated very often, perhaps once a minute or so.
> >
> >Do you mean I should have two way communication with the time/temp
systems?
>
> In one word, yes. Master Stamps sends an addressed inquiry, and only the
> addressed
> unit responds. It MUST respond, else you know there is a dead unit. If it
has
> no data, it just sends NADA (or something) otherwise it sends the
> appropriate data. If all the remotes were permitted to broadcast at or
near
> the same time, on the same frequency, you'd have a bunch of jumbled data.
> Sound familiar :-)
>
> One alternative might be to use spread spectrum (cell phone) technology.
> Many units can then coexist at, near, or on the same frequency. I'm just
> not sure what the FCC might have to say about that. OTOH if it were done
> with SMS messaging, what could they say :-)
>
>
> >Jonathan
> >
> >www.madlabs.info
>
> Bruce
>
>
> To UNSUBSCRIBE, just send mail to:
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> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>
"One alternative might be to use spread spectrum (cell phone) technology.
Many units can then coexist at, near, or on the same frequency. I'm just
not sure what the FCC might have to say about that. OTOH if it were done
with SMS messaging, what could they say :-)"
about using cell phone and sms messaging now what tipe of modem or cell will
work with BS2 to do this?
Thanks
Mensaje original
De: Bruce Bates [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=fcncNxUaFCyzjKVSiM3Z0R8BCP_X4ZUOjAgQx6ppAbCvYiI6N7TRQsd77FrigkkNgYr5Z7QnACvayShi]bvbates@u...[/url
Enviado el: lunes, 17 de noviembre de 2003 13:38
Para: basicstamps@yahoogroups.com
Asunto: Re: [noparse][[/noparse]basicstamps] Multiple wireless data on same freq.
At 09:31 AM 11/17/03 -0800, Jonathan Peakall wrote:
>Bruce,
>
>
> > Use the master Stamp to poll each of the remotes in turn. Don't try to
>have
> > the remotes transmit randomly. If they have nothing to send then they can
> > say just that. A round robin kind of deal.
>
>I don't think I understand what you are saying. Perhaps I didn't explain the
>set up well enough.
>
>The time and date are being constantly broadcast. I need to do this, as at
>least one of my applications is very time critical (a seismograph). The
>temp. and humidity reading are of course low priority, and don't need to be
>updated very often, perhaps once a minute or so.
>
>Do you mean I should have two way communication with the time/temp systems?
In one word, yes. Master Stamps sends an addressed inquiry, and only the
addressed
unit responds. It MUST respond, else you know there is a dead unit. If it has
no data, it just sends NADA (or something) otherwise it sends the
appropriate data. If all the remotes were permitted to broadcast at or near
the same time, on the same frequency, you'd have a bunch of jumbled data.
Sound familiar :-)
One alternative might be to use spread spectrum (cell phone) technology.
Many units can then coexist at, near, or on the same frequency. I'm just
not sure what the FCC might have to say about that. OTOH if it were done
with SMS messaging, what could they say :-)
>Jonathan
>
>www.madlabs.info
Bruce
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
> Bruce,
>
> Sounds like I best stick to different frequencies. I
> would have to add an
> transmitter to every project using the time base,
> which is currently 3 and
> growing.
I don't know all the details of the project, but on
the assumption that the radio is 2-way, you could
prompt the two sensor devices for data? Each unit
could be set to respond to a sepcific string I.D. on
that frequency...?
=====
Chris Savage
Knight Designs
324 West Main Street
Montour Falls, NY 14865
(607) 535-6777
http://www.knightdesigns.com
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Then I have to have a transmitter and receiver on each device, making it all
a lot more expensive.
Jonathan
Original Message
From: "Chris Savage" <knight_designs@y...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, November 17, 2003 10:56 AM
Subject: Re: [noparse][[/noparse]basicstamps] Multiple wireless data on same freq.
> --- Jonathan Peakall <jpeakall@p...> wrote:
> > Bruce,
> >
> > Sounds like I best stick to different frequencies. I
> > would have to add an
> > transmitter to every project using the time base,
> > which is currently 3 and
> > growing.
>
> I don't know all the details of the project, but on
> the assumption that the radio is 2-way, you could
> prompt the two sensor devices for data? Each unit
> could be set to respond to a sepcific string I.D. on
> that frequency...?
>
>
>
>
> =====
> Chris Savage
> Knight Designs
> 324 West Main Street
> Montour Falls, NY 14865
> (607) 535-6777
>
> http://www.knightdesigns.com
>
> __________________________________
> Do you Yahoo!?
> Protect your identity with Yahoo! Mail AddressGuard
> http://antispam.yahoo.com/whatsnewfree
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>
> Chris,
>
> Then I have to have a transmitter and receiver on
> each device, making it all
> a lot more expensive.
Sorry Jonathan,
I don't always read all the threads, then I see a
message I comment on and don't have all the details.
It would seem that 2 devices transmitting on the same
frequency at the same time would be hard to read, but
let me ask you this, does each device transmit an I.D.
with each data packet?
=====
Chris Savage
Knight Designs
324 West Main Street
Montour Falls, NY 14865
(607) 535-6777
http://www.knightdesigns.com
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Protect your identity with Yahoo! Mail AddressGuard
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Thanks for the link you sent off list. It made some stuff clear to me. I
thought I'd answer here, as this might be of interest to others, I don't
know.
So, how about this: I put a receiver with the temp and humidity sensor. It
detects when the time transmitter sends a burst of data, waits until it
finishes, then sends its data. That way, the receiving devices will not need
a transmitter, and the time signal remains the top priority. Any other
sensors or transmitting devices will cascade after the time has been sent.
All future remote data sending devices will have to have both a transmitter
and a receiver, but at least the existing receiving devices can remain as
they are.
Sound like that would work?
Thanks for the help,
Jonathan
www.madlabs.info
>
> I want to be able to use the same frequency to transmit serial data from
> wireless RF sensors. Currently I have a WWVB linked system broadcasting the
> time on 433mHz, and I have a SHT11 based temp. and humidity sensor
> transmitting on 315mHz. I want to run the SHT11 on 433mHz as well, because
> that way one receiver in the weather station I am building can get both data
> sets.
>
> So, I have been trying with the WAIT modifier, and even with three
> characters to recognize, I am still getting a lot of false readings. Is it
> possible to do this reliably?
>
> Jonathan
>
> www.madlabs.info
Using two transmitters operating at the same frequency, in the same air-space,
will
cause data collisions. There's really nothing you can do to get around this
problem
unless you setup at least one as a master to manage network traffic or use
hardware
like the MaxStream http://www.maxstream.net frequency hopping radios.
I use our TXLC/RXLC modules in a similar way, but I have 1 TX & 1 RX at each
station.
The master polls each remote address for new data. A simple way to reduce errors
is
to send each data packet twice. Verify packet #1 against packet #2, and process
them
only when there's an exact match between both data packets.
This method requires more time, and a little more programming on both ends, but
it's very
simple and still considerably less expensive than using higher-end RF gear for a
Stamp
project.
The chance of receiving two corrupt data packets that are an exact match when
compared
byte-for-byte is pretty slim.
Just remember, when you run two transmitters at the same frequency, at the same
time, in
the same air-space, it's like throwing two buckets of water up in the air and
trying to determine
what water came from which bucket when it lands. This is what your receiver
sees. A mixture
of bits all mingled together that it can't make sense of.
Regards,
-Bruce
tech@r...
http://www.rentron.com
>Bruce,
>
>Thanks for the link you sent off list. It made some stuff clear to me. I
>thought I'd answer here, as this might be of interest to others, I don't
>know.
>
>So, how about this: I put a receiver with the temp and humidity sensor. It
>detects when the time transmitter sends a burst of data, waits until it
>finishes, then sends its data. That way, the receiving devices will not need
>a transmitter, and the time signal remains the top priority. Any other
>sensors or transmitting devices will cascade after the time has been sent.
How will each of them determine when "now" is ? Will each be assigned it's own
time slot ? If, that may be one way to orchestrate it.
>All future remote data sending devices will have to have both a transmitter
>and a receiver, but at least the existing receiving devices can remain as
>they are.
>That keeps the problem from getting any worse.
>Sound like that would work?
>Give it a shot. Nothing ventured, nothing gained :-)
>Thanks for the help,
>Sure
>Jonathan
>
>www.madlabs.info
Bruce
>
> How will each of them determine when "now" is ? Will each be assigned it's
own
> time slot ? If, that may be one way to orchestrate it.
>
We'll call the time signal device A. In a sense, it is the master, as it's
signal is highest priority. Device B waits for devices A's data burst. Then
device C waits for device B's data burst, and so on. I won't be able to run
too many devices this way, as I have to keep it all well under one second to
keep the clocks correct, but I can squeak a few in.
I'm going to order some stuff today and try it out.
Jonathan
www.madlabs.info
There are a lot of ways to have multiple messages sent over a channel.
The GPS system uses the same frequency for all the satellite
transmitters using what's called CDMA, Code Division Multiple Access.
Another protocol is Time Division Multiple Access. Each transmitter has
an assigned time slot.
Frequency Division Multiple Access is like the normal radio or TV where
each transmitter is on it's own frequency.
Some early ham radio internet work was done with random transmissions
and collision detection at the receiver, this works if the network is
lightly loaded. This might work for you since it doesn't require
listening prior to sending.
Another approach would be to use Single Side Band modulation (same as AM
modulation, except there's no carrier and one of the sidebands is also
removed) and a different audio frequency for each transmitter, similar
to telemetry systems where each sensor modulated a different audio
tone. This is equivalent to a FDMA system where all the channels are
within the passband of the receiver. A single receiver could receive
all of them and they were separated using audio filters. Note that in an
FM system the strongest signal captures the receiver and none of the
other signals are heard. This is why aircraft radios use AM, you can
hear a weak signal in the presence of a strong signal, vital where
safety is so important.
73,
Brooke Clarke, N6GCE
http://www.PRC68.com
>Date: Mon, 17 Nov 2003 11:08:18 -0800
> From: "Jonathan Peakall" <jpeakall@p...>
>Subject: Re: Multiple wireless data on same freq.
>
>Chris,
>
>Then I have to have a transmitter and receiver on each device, making it all
>a lot more expensive.
>
>Jonathan
>
>
>
>
>
>
>