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sid111sid111 Posts: 5
edited 2006-10-25 19:12 in BASIC Stamp
I·try to use ·RF transceiver package to compose bi-direction communication between pc and BS2.when·I test one direction individually
(pc to bs2 or bs2 to pc) ,everything was okay..but when·I connect two transistor at the same time, here comes the trouble.....my receiver got
lots of·incorrect·information.· I just connect 5V,GND,ADTA Pin· of transistor and receiver,and my code were just use serout command to sent data.
Is any important thing·about bi-direction communication I·have to do ?

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-10-24 17:54
    Hello,
    ·
    ·· During bi-directional communication with the systems on the same frequency/channel you need to be sure only one side is talking at any given time.· The easiest way to do this is to designate one as the host and the other as the remote.· The host will query the remote for information or initiate all communication when it’s ready.· I hope this helps.

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    Chris Savage
    Parallax Tech Support
  • sid111sid111 Posts: 5
    edited 2006-10-25 00:06
    Hi,
    yes, i had try it before. I use PDN pin to cotrol two transistor when one is sending data the PDN is high ,the other's PDN is low.
    But the data wasn't 100% correct .Maybe just a part of data or even no any part of data displayed on my pc but jsut like press an enter to change line. What's the problem is??? Please tell me, thanks!!
  • Kevin WoodKevin Wood Posts: 1,266
    edited 2006-10-25 00:53
    The general reason that you can't have two tramitters transmitting on the same frequency at the same time is that the signals will interfere with each other.

    One signal will overpower the other signal, or else the receiver will try receiving both signals simultaneously, in which case it will receive pieces of info from each signal.

    If you want to transmit & receive simultaneously, you need to use different frequencies between the tranceiver pairs. So if you have two frequencies, A and B, it would look like this:

    PC: transmit on freq A, receive on freq B
    BS1: transmit on freq B, receive on freq A
  • sid111sid111 Posts: 5
    edited 2006-10-25 15:30
    hi, Kevin

    I know the interfere between two transisor with same frequency ,but I'm not familiar with RF device really.So , I don't know which RF device's frequency is not 433MHz .
    If any RF device's frequency is not 433MHz, the problem will be very simple.
    Can you recommand me some Rf device to use ?? thanks
  • Tom WalkerTom Walker Posts: 509
    edited 2006-10-25 16:56
    The Parallax products are fixed on 433. Since the Stamp is a single-tasking device, it would do no good to have two frequencies. The kind of communication that can be implemented on the Stamp is called Half-Duplex, in which only one side can be transmitting at a time. You must manage the "two-way" communication by desigining a protocol for your project which allows one side to be in charge of who gets to transmit when.

    This has been covered elsewhere in the forum.

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    Truly Understand the Fundamentals and the Path will be so much easier...
  • Martin HebelMartin Hebel Posts: 1,239
    edited 2006-10-25 19:12
    Since you asked about other RF devices, there are XBee units that operate on 2.4GHz, and though data can only in one direction at once, the devices have buffers to hold the data to be sent and when received. They wait until no other device is transmitting on their frequency channel before sending. Also, the devices can have unique address and unique frequency channels so data only goes to particular unit or units.

    http://www.selmaware.com/appbee

    -Martin

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    Martin Hebel
    StampPlot - Graphical Data Acquisition and Control
    AppBee -·2.4GHz Wireless Adapters & transceivers·for the BASIC Stamp & Other controllers·
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