Ten SureLink 900 MHz RF transmitters sending data to only one SureLink 900 MHz

Joe

Hi,

Only to know if it is possible to send
ten SureLink 900 MHz RF data to only one SureLink 900 MHz RF receiver.


I need to collect data sensors from ten basic stamps and send this
data to one basic stamp using SureLink 900 MHz RF modules.

Any input ?

Thanks, Joe

Newzed

On your Tx Stamp 1, serout...[noparse][[/noparse]"A", data]
On your Tx Stamp 2, serout...[noparse][[/noparse]"B", data]

and so on.

On your receiving Stamp write serin...[noparse][[/noparse]WAIT("A"), com (or whatever]
········································· serin...[noparse][[/noparse]WAIT("B", com]

and so on.

The WAIT bytes act like an address.· Your receiving Stamp can process
the "A", "B", etc., anyway you like.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html

·

Paul Baker

I am not familiar with the RF module, but I have some concern of the 10 transmitting devices "stepping on each other's toes" trying to communicate simultaneously with the receiver. The modules have error correction, but any EC algorithm can only fix the data if the number of errors is below a maximum number of bits. Since the RF modules are transceivers, you can program them to operate in a request-reply mode. The receiver stamp will send a command requesting the first sensor·stamp for data, which responds with the data, the receiver stamp does this in round robin with all the sensor stamps. Since the sensor·stamps only speak when spoken to, the air will be as clear as possible to reduce the bit error rate.

Post Edited (Paul Baker) : 7/13/2005 11:22:35 PM GMT

Jonathan

Paul,

I came here to reply, and found you had said exactly what I intended to say. There is no way that ten transmitters are NOT going to step on each other. Since the modules are transeivers, you can do as you say and "poll" the sensors one at a time.

Jonathan

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.madlabs.info - Home of the Hydrogen Fuel Cell Robot

Bruce Bates

Gents -

Just one thought to add to this discussion. There seems to be a presumption that is unstated in the questioner's first posting. Admittedly I don't know much about the Surelink Transceivers, so this thought may be way off base. If this broadcasting is being done with only one frequency, all that's been said so far, holds true.

If, however, there can be 10 different frequencies in the 900 MHz band, each slave assigned to one of these frequencies, then the "HOST" receiving the data can scan those 10 assigned frequencies, looking for activity.

I have no idea whether this reperesents an FCC (or other regulatory body) "approved use" of this particular band. Just another, possibly faster, method of doing the polling, if the tranceiver is capable of such frequency shifting/scanning.

Regards,

Bruce Bates

Chris Savage

Bruce,

·· The SureLink RF Modules do in fact support multiple channels.· More information can be obtained here:

http://www.surelinkrf.com



▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com

steve_b

900Mhz is still part of that "hobby" band (can't remember the abbreviation they use....EMD or something).
So long as you are below a certain power and not interfering with other "licensed" devices on other bands....they won't say much.

If however, your cheap 900Mhz phone is interfering with your neighbors....they might make issue as this is disrupting an emergency calling device (if you have to dial 911 and the thing won't work cuz of the interference then someone might be injured or otherwise!).

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·

Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Tim-M

Guys,

Even if all units are on the same frequency, couldn't a strategy be used something like this:

Each of the ten Surelinks could be 'named' or have a designating character assigned in order to tell them apart, then have all of them remain silent until the receiving module requests data from a specific named module - that way only only one module is transmitting at a time, and the receiving module can work its way through the ten others one at a time - ask for data, wait to receive it, if things look good move on to the next, if not ask for the data again... etc.· The Surelink modules are transceivers after all, so this scheme seems workable to me.· What do you think?

Tim

Paul Baker

About the multiple channel idea, the RF module supports 9 channels. If each transmitter is transmitting on its own frequency (forget the fact that you have 1 too few channels), there is potential for loss of data. This may be unimportant for this application, but if a sensor stamp sends a data packet while the receiver stamp is on another channel, that datapacket is missed, if the sensor stamp goes to transmit the next datapacket, the previous data packet will have been lost becuase noone was listening. You could have each sensor stamp retransmit the data until the receiver stamp sends an acknowledge packet. But this system will consume alot more power because the sensor stamps are continually sending data.

One thing to note is if you are in an urban area such as an apartment complex and you are flooding the 900MHz band on most if not all channels, you can bank on a neighbor making a complaint that their cordless phone is no longer working. I came home last night to a truck from our local power company·slowly driving through our complex holding a directional antenna out of the window and pointed at our buildings. Im not exactly sure what he was doing, but it was clear he was "sniffing the air".

Paul Baker

Tim-M said...
Guys,

Even if all units are on the same frequency, couldn't a strategy be used something like this:

Each of the ten Surelinks could be 'named' or have a designating character assigned in order to tell them apart, then have all of them remain silent until the receiving module requests data from a specific named module - that way only only one module is transmitting at a time, and the receiving module can work its way through the ten others one at a time - ask for data, wait to receive it, if things look good move on to the next, if not ask for the data again... etc.· The Surelink modules are transceivers after all, so this scheme seems workable to me.· What do you think?

Tim

Isn't this the same as this:

Paul Baker said...


Since the RF modules are transceivers, you can program them to operate in a request-reply mode. The receiver stamp will send a command requesting the first sensor·stamp for data, which responds with the data, the receiver stamp does this in round robin with all the sensor stamps. Since the sensor·stamps only speak when spoken to, the air will be as clear as possible to reduce the bit error rate.

??? (I am not trying to chastise you, so please don't read any animosity in this post).

Tim-M

Paul Baker said...

Tim-M said...
Guys,

Even if all units are on the same frequency, couldn't a strategy be used something like this:

Each of the ten Surelinks could be 'named' or have a designating character assigned in order to tell them apart, then have all of them remain silent until the receiving module requests data from a specific named module - that way only only one module is transmitting at a time, and the receiving module can work its way through the ten others one at a time - ask for data, wait to receive it, if things look good move on to the next, if not ask for the data again... etc.· The Surelink modules are transceivers after all, so this scheme seems workable to me.· What do you think?

Tim

Isn't this the same as this:

Paul Baker said...


Since the RF modules are transceivers, you can program them to operate in a request-reply mode. The receiver stamp will send a command requesting the first sensor·stamp for data, which responds with the data, the receiver stamp does this in round robin with all the sensor stamps. Since the sensor·stamps only speak when spoken to, the air will be as clear as possible to reduce the bit error rate.

??? (I am not trying to chastise you, so please don't read any animosity in this post).


Yep, sure·sounds like it to me to·Paul.· My apologies, I missed that post entirely.... no worries, no animosity taken!

Tim

Chris Savage

Paul Baker said...(trimmed)
About the multiple channel idea, the RF module supports 9 channels. If each transmitter is transmitting on its own

Paul,

·· Perhaps I will have to re-read the documentation.· I haven't used multiple channels, but the software indicates support for 15 channels, I believe.


▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com

Paul Baker

No problem, I too have a tendancy to gloss over posts and miss important elements.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

Paul Baker

I yanked that number straight from Parallax's documentation on the product, here is the section of the pdf:

Chris Savage

Paul,

·· There does seem to be some discrepancy at the information we have been provided in the past compared to what seems to be available now.· This was recently being addressed, hence the referral to the product page from the manufacturer.· Apparently there has been some changes recently, of which we were not aware of.· This is currently being handled, however.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com

Paul Baker

Ah, I understand, I was a little confused why you pointed to the manufacturer's website, especially since I was unable to find any user manual for the product on thier website (except for that paultry page overviewing features and operating modes). And sure enough looking over the page again I see "Up to 16 Channels (4 User Configurable)". I hope you guys make sure the older versions in your stock are accounted for before updating the manual, wouldn't want someone who thought they were purchasing a 16 channel RF module actually get a 9 channel module.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

Chris Savage

·· Yeah, it's rare, but once in awhile a product spec changes without our immediate knowledge or notification.· When this happens some information may become out of date, inaccurate or obsolete.· It's been Parallax's goal to always provide clear up to date and useful/helpful documentation for the products we carry.· To that end you can rest-assured we'll be updating the documentation as soon as we're sure we have all the correct information.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com

steve_b

How big is the guard band between channels?
Wonder what the selectivity is on teh receiver.....obviously must be alright if it's built for this...

Anyhow, do you need all the data at the same time (for each minute on the minute)? Or can you have the stamp hold that previous minutes reading for a bit.
What you could do then is try to time sync them all (hard to do...even with the DS1620....all IC's drift differently).

But Paul is right about listening to one channel while a 2nd channel transmits.
Having it constantly tx while you are scanning channels is another way too (but then the sensor side stamp will be busy transmitting instead of listening to the sensor).
And I assume these are transceivers (transmitters AND receivers)? bidirectional comms eats up more time to do other things too....it'd be nice to have everything one way!

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·

Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Robert Kubichek

Joe said...
Hi,

Only to know if it is possible to send
ten SureLink 900 MHz RF data to only one SureLink 900 MHz RF receiver.


I need to collect data sensors from ten basic stamps and send this
data to one basic stamp using SureLink 900 MHz RF modules.

Any input ?

Thanks, Joe

I would use the one as a master, that polls each slave that transmits data three times so the master can compare each to verify/error correct.
At a higher baud rate it should not take long to transmit a string x3 , so depending on amount of data each sends, you could then figure out your max sample
rate...

Bob N9LVU

Paul Baker

The modules have built in error correction, performing your own EC isn't nessesary and just adds code and slows down execution time. However you should catch situations where the EC of the module fails to correct the data due to too many bit errors so you can request another copy from the sensor stamp.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

Joe

Thanks:


But It is not necesary to send the data from each SURE LINK RF transmitter at the same
time. Is it a temperature alarm from 10 differents point with ten ds1620 chips total.

If the temperature from one point raise then I need to send the alarm to the
(only one) receiver and then move a servo motor.

I was thinking in the frequency, because if I have ten transmitters
I think that I will have 10 differents frequencies and I don't know
if all modules has the same frequency or if they are matched or
sold by pairs.

Is the sure link usefull?

Thanks: Joe

Paul Baker

Part 1:

Joe, what we are trying to say is that you can't send all the data at once. If they are on the same frequency, the receiver will only see a bunch of undeciferable garbage. If you have them on different frequencies, the receiever can only be on one frequency at a time, so it still cannot receive all the data at once.

If you are using these sensor stamps only to send alarm indicators, you shouldn't put the transmitters on different frequencies. You are much more likely to miss that message. Place them all on the same frequency. There still is a possibility of two sensor stamps reaching alarm status simulaneously, so when a sensor stamp reaches alarm status it should transmit, wait a random amount of time, retransmit, wait a random amount of time, retransmit,... This way the receiver stamp should eventually get the message. Also the receiver stamp can infer that the sensor stamp is out of alarm status when it has stopped receiving the alarm status after a few periods of the maximum random waiting time.

As per the usefullness, frequently the Parallax staff experiment with the products they sell. Chris would be better able to say what the staff's experience with the product is.

Part 2:

I think I may have come up with a better solution, to the temperature logging scenario.·Joe, since your not doing this stick with the above method. Im only posting this because I came on specifically to share this, and wrote it before I saw you response and intended use for the system.

You're already going to have an identifier for each sensor stamp, have the sensor stamps do thier own round robin.

Each sensor stamp will set the surelink to receive except the sensor with the lowest ID.·That one·will send its data to the reciever stamp, the sensor stamp with the next highest number will see that transmission itself and know it is next in line. After a set amount of time, it will send its data. This goes on with all 10 stamps each getting thier cue from the sensor before it, with the first sensor stamp getting its cue from the last sensor stamp.

Now there is a potential pitfall with this scheme, and thats when one of the sensor stamps is offline. If you don't account for this possibility, the transmissions will stop because the next sensor stamp wouldn't get it's cue. So after the expected time period happens and the next stamp does not see the transmission from the previous sensor stamp, it knows it is deactived. So it does another time interval then transmits it's data. All the sensor stamps must note these "down sensor stamps" because more than one may be out of comission, so the next in line needs to know its expected place in line even if multiple stamps before it are down. You can think of this as being a periodic transmission where each sensor stamp's place is offset a certain amount, the listening to the channel causes all the sensor stamps to synchronize thier position with the other stamps. If you are sending data from all sensors every 10 seconds, the first will transmit at time 0, the second will know it transmits a second after that, and so forth.


Post Edited (Paul Baker) : 7/14/2005 10:33:39 PM GMT

stamptrol

· Hi Folks,

····· At the risk of adding more comment to an exhaustive discussion. Here's

how we do RF links with various manufacturer's radios, including SureLinks.

Our application is similar to the one in this thread, except we are also sending

control instructions to the field units as well.

···· 1. Configure the base SureLink unit ( or master, if you will ) as unit 'A'

as per the SureLink data sheets.

···· 2. Configure all others as unit 'B'.

···· 3. The master polls the remote 'B' units one at a time. When the 'B' unit Stamp

hears its address, it responds. The master can try a couple of times, if required

to check that valid data was received. Similarly, if the Master sends a command

to the remote unit, it includes the address, so the remote units will only respond

if they are supposed to.

··· 4. This system is patterned on the tried and true RS-485, 2-wire system

of networking. It eliminates the need for each part of the system to have unique

characteristics.

··· 5. The intelligence is in the Stamps at either end, not in the link elements.

··· Regards,

·· Tom Sisk