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From: firstname.lastname@example.org (john jardine)
Subject: Re: Help needed with my A-level project - RF link
Date: 2 Nov 2002 06:47:36 -0800
NNTP-Posting-Date: 2 Nov 2002 14:47:36 GMT
"Sanjeevan" wrote in message news:...
> The data I'm going to be sending is going to be in the form of 8 bits at a
> time. So for
> example if I send BYTE A:"1 1 1 1 1 1 1 1", then send BYTE B:"0 0 0 0 0 0 0
> 0", how can I
> prevent the reciever from picking up a mixture of BYTE A and BYTE B (e.g. "1
> 1 1 1 0 0 0
> 0")? Will i need to synchronise the digital clocks on the transmitter and
> As an A-Level project, it does not have to work properly, or work at all.
> What I want is to
> get the theory behind the project correct, and have a basic schematic of all
> which make up this project, e.g. mixer, filter, amplifier.
> I would appreciate any comments on how to improve this design, or any help
> in general.
What you have sorted out *is* perfectly doable and sounds a nice
project. The only oddity (as you've figured out) is picking up the
correct strings of binary at the receiver end. You've come across
-the- standard serial comms 'poser' and as a simple solution I'd look
at the way its done on a PC 'serial' com1/2 cable (the "RS232", you
don't need parity ect).
The idea is to simply 'encase' each and every single data byte before
is sent with some fixed extra bit(s) (eg always add a "1" before and a
"1" after the 8 bits of data) that will allways be present at the
receiver end no matter what the actual byte data is. If the data is
"00000000" you send"1000000001".
At the transmitter send these bits out at a fixed rate. At the
reciever check the bits in at the same rate. Look out for the
"starting" bit, then check at 8 fixed intervals for the "data" bits.
Make sure the stop bit is there and then go back to checking for the
start bit of the next data byte.
The TX/RX system will be synchronised (and stay that way) after the
first byte is received. The Tx/Rx data clock frequencies only need to
be within a couple of percent as the byte to byte error is non
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