AVR-Chat

It appears you send a sync character at the start of each frame. 

You could use this sync character to activate the receiving UART... Just
tie the receive data line to a timer capture/compare input. Have a
window of time that represents a valid bit, and when you receive a
sufficient number of valid bits (timer capture interrupts) then activate
the USART.

Best of luck,
Dave

On Tue, 2005-03-22 at 13:39 -0300, Javier Fiasche wrote:
> That's right the uart ist triggering on noise. 
> Unfortunatelly my reciever does not have signal strength output. I am
> using a very cheap 
> Yong Horng reciver and transmitter (not a transciver).
> I would need to detect a real transmition and to reject noise, but
> digitally, ideas???
> I tried transmitting a Hi level before setting the uart to transmitt,
> and trying to detect this continuos hi level on the reciver before
> setting the reciever uart to recive, But it doesn't work that
> fine............
> Thanks
> Javier
>  
> -----Mensaje original-----
> De: Bruce Parham [mailto:obparham@jpl.nasa.gov]
> Enviado el: Martes, 22 de Marzo de 2005 01:29 p.m.
> Para: AVR-Chat@yahoogroups.com
> Asunto: Re: [AVR-Chat] RF link
> 
> 
> 
> 
> Javier Fiasche wrote:
> > 
> > Hi everybody, i'm having trouble.....
> > 
> > I am trying to transmit data over Rf using 2 atmega8l(via USARt) and
> 433Mhz
> > transmitter and reciver module. One will work as transmiter and the
> other as
> > reciever. The transmiter will send a code composed of:
> >         -----------------------------
> >        | SYNC |Package|CHECKSUM|end|
> >        -----------------------------
> > all of this coded as manchester. Afer sending the package, the mega8
> will
> > shut down the transmitter until next transmition.
> > The reciever would listen to the reciver module only when it is
> desired,
> > selecting this with a pushbutton.When i dont want to listen, i shut
> down the
> > 433 reciver module
> > Here is the problem:
> >         i dont seem to sincronice the transmitter and the reciver
> usart, because
> > when the transmitter is off and the reciever is on i keep getting
> and
> > Framming error.
> >      i've tried listening to the RXd pin, with the RXEN=0, till i
> get a
> > long enought "1" and then set the RXEN=1, but this seem to have no
> > effect.........
> > Any ideas of how to sincronice them????????????
> > 
> > Thanks
> > Javier
> 
> Sounds like the rx doesn't have any squelch and the uart is triggering
> on noise.
> I don't know what kind of receiver you're using but, if it has a RSS
> (Rx Sig Strength)
> line, you could use that to enable/disable the rx uart. (You may need
> to use the 
> analog comparator on the RSS signal.)
> 
> Bruce
> 
> 
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