Jee Labs Talk

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1. pic
   

   Hi

   Nice web, with lot of nice information:-):-)

   Your project with the RF12B RF unit interest me a lot. I have some module myself, and planing to make a project with them.
   But I want 4 unit collecting information, and only 1 unit receiving the result. I can see in your fw that you have unit numbers, "(set node ID (standard node ids are 1..26))"? But you have all the unit's on the same frequency, or...? Will it say you prefix each unit and the in the receiver poll for the right one?

   Some hints...

   Posted 06/09/2009 16:00:20

2. jcw
   

   The RF12 driver works with all nodes on the same frequency. When sending to "node 0", this is interpreted as a broadcast. All packets sent are received by everyone, but the receiver code will only report packets sent to its node number and packets sent to node 0, so the idea is that one node accepts those 0-node packets and sends an acknowledgement back to the sender if requested.

   There is also the notion of a "network group". Only nodes within the same group see each other, so you can have lots of nodes grouped in various ways. Each group is logically independent of the other, the RF12 driver will not report packets from a different group (it still receives it completely, but it'll silently ignore a packet from another group than its own).

   I'm probably making this look much more complicated than it actually is...

   Another attempt: 1) put the nodes you want to communicate with each other in a single group, 2) give each node a different ID, 3) let all nodes except the central one broadcast to node ID 0, 4) let the central node accept packets sent to node 0, and 5) let the central node send an ack back to the sending node when requested.

   Does this help?

   Posted 06/09/2009 19:58:14

3. pic
   

   Thanks for your nice explanation.

   But i still have some understand problem with the unitID.

   All the units running on the same freq, right? The only differ is the ID in your software, right?
   Therefore I cant understand how to handle more than one unit sending data at the time.
   Lets say we got 4 unit collecting data, the unit must have different ID ex. ID1-ID4.
   Only 1 unit are receiving the result from all the collectors, maybe this can be ID5.
   The ID is don't care because it is only receiving data, right?

   How to prevent data corruption at the receiver side, when more than one is sending at the time, in the same grouping.

   Is there something I misunderstand?

   I understand your grouping and use of pattern match, it's smart to use the hardware in the RF12 on that way:-)

   Regards

   Posted 07/09/2009 10:33:41

4. jcw
   

   Ah, now I understand where you're coming from...

   Yes - same frequency. The current design assumes a low packet send rate, with plenty of time in between. When two transmitters send at the same time, they will both fail - just as they would when some other non-JeeNode is sending something on 868 MHz. So they must either attempt to re-transmit later, or ignore the failure and try again with new data the next time.

   If an acknowledgement is requested and received, then the receiver knows it has successfully sent the data across.

   There is no [i]listen-before-send[/i] in the current driver, which would slightly reduce the number of collisions. Nor is there any logic right now to reduce the bandwidth to run a few separate narrow channels next to each other.

   The 433/868/915 MHz bands are "ISM" bands, intended for [i]occasional[/i] sending of packets. There is no mechanism to rule out collisions, or even to be certain the radio channel is available and free from interference. That's why it's intended for low-rate signaling, not for continuous streaming.

   Posted 07/09/2009 14:06:00

5. pic
   

   Hi

   Thanks for taking your time to explain. Nice and clean explanation, thanks for that.

   Regards...

   Posted 07/09/2009 18:19:51

6. bennyjo88
   

   Hi
   Tks a lot for making the RF12B library and enabled the beginner like me to use it easily.

   I have a similar question like the above, but the scenario is the other way around.

   I like to have one transmitter unit and three receivers (A, B, C) unit. Let's say, the transmitter have 4 buttons, PB0, PB1, PB2 and PB3. If I press PB0, it broadcast to all data packet (this part I understand, using broadcast mode, nodeID 0), but how do I setup, if I press PB1, send data packet to receiver A only, PB2 to B, PB3 to C? Do I need to use different "node ID" or "Network Group" to do so?

   Tks n regards...

   Posted 08/09/2009 06:10:37

7. jcw
   

   Single network group, different node ID's. Give your transmitter a different node Id too, then send to 0 = all, 1 = PB0, 2 = PB2, etc. Do not use acknowledgements when sending to all, because then all nodes will try to ack at the same time.

   Posted 08/09/2009 14:11:13

8. bennyjo88
   

   tks a lot JC, very clear.

   Posted 08/09/2009 23:42:28