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farazwan
Joined: 26 Apr 2012 Posts: 13
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how to receive data from two slave using Zigbee??? |
Posted: Thu May 17, 2012 9:19 am |
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I've successfully received adc data from a slave. Now, I want to receive adc data from two slaves. Can anyone help me??? |
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dyeatman
Joined: 06 Sep 2003 Posts: 1924 Location: Norman, OK
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Posted: Thu May 17, 2012 2:59 pm |
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Farazwan, you're a fountain of information but we are not mind readers. If
this is related to a post you made earlier you should add to that. If not then
give us something to go on like what you have right now both H/W and
software and maybe some code? _________________ Google and Forum Search are some of your best tools!!!! |
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farazwan
Joined: 26 Apr 2012 Posts: 13
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Posted: Fri May 18, 2012 1:41 am |
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bnh
Last edited by farazwan on Sun May 20, 2012 11:04 am; edited 1 time in total |
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Ttelmah
Joined: 11 Mar 2010 Posts: 19360
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Posted: Fri May 18, 2012 8:54 am |
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From what I'm 'guessing'. you probably can't....
You need to understand the difference between a 'simplex' link, a 'half-duplex' link, and a 'duplex' link. It sounds as if you have the first. A single 'transmitter' module on one device, and a receiver on the other. You are asking how to have multiple transmitters all send messages to the single receiver?. This is like having one person standing in a crowd, while several other people (who have their own ears blocked), try to shout messages at him. Unless one happens to 'strike lucky', and shout at exactly the moment when everyone else is silent, none of the messages will get through. This is a 'simplex' link - only one direction possible.
Now, there is a strategy, that _can_ possibly allow this to sort of work. What you have is one transmitter send messages (with an ID attached to say who they are from, and a 'checksum'), at intervals of (say) 1 second. Then the second transmitter sends messages at a fractionally different interval - perhaps 1.01 seconds. Keep the messages short, so the gaps between are long. Then the receiver looks for a message with a good checksum (this way if two messages are sent at the same time, both will be rejected), and works out who each message is from. If two messages 'clash', because the interval between is not the same, they will get corrupted, and the checksum will fail. However the next pair of messages will 'miss' one another, because the timings are different. A 'brute force' solution, but one that can work reliably, provided missing one message doesn't matter.
If messages 'matter', then a more complex solution is needed. This is where you switch to 'half duplex'. Here the people in the previous analogy, don't have their ears covered (so you current transmitting device, would have a receiver as well), and the man wanting the messages, 'asks' for them. He shouts 'one', and the first 'slave' responds with it's message. He then shouts 'two' and the second slave responds. Here messages can go in both directions, but only one way at a time. This is called 'half-duplex' (two way transmission but only one way at a time). With this you can also have 'hand along' as a strategy - here the master says 'anyone there', and the first 'slave' responds, but when it finishes adds at the end of the message, the header to tell the _next_ slave to now respond.
The third solution is 'full duplex'. You have a second radio link, using a different frequency (so data can be sent both ways at the same time). This is fine for wires, but gets expensive on frequencies for radio. However the requests can then be much faster.
Best Wishes |
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