sending digital signals over radio

[margoob]

I've got a 8-bit signal which I want to send over radio - which would
be received & decoded into the 8 bit signal - how do I do it???

I was thinking of taking the signals into a 1 bit shift register - but
decoding that signal from the rx side is getting really complicated...

any suggestions?

 

[Robert Baer]

I've got a 8-bit signal which I want to send over radio - which would
be received & decoded into the 8 bit signal - how do I do it???

I was thinking of taking the signals into a 1 bit shift register - but
decoding that signal from the rx side is getting really complicated...

any suggestions?

Hmm..8 bits..ASCII..Baudot..RS232 ports...sounds simple to me.

 

[Andrew Holme]

I've got a 8-bit signal which I want to send over radio - which would
be received & decoded into the 8 bit signal - how do I do it???

What range / frequency / data rate do you need? You can also get
off-the-shelf RF modules for short range serial data links.

I was thinking of taking the signals into a 1 bit shift register - but
decoding that signal from the rx side is getting really complicated...

any suggestions?

You could use a UART (Universal Asynchronous Receiver/Transmitter). This
chip does it for you. They're used in RS232 serial ports. They work by
adding a "start bit" to the front of your data. From the middle of the
start bit, the receiver counts 8 bit periods to find the centre of each data
bit. Micro-controllers (e.g. PIC) often have a UART built-in.

 

[Dr Chris Andrews]

I'd use a UART at the transmitting end (FIFO if you have bursts of data) -
parallel in, formats the data into a serial stream, output serial stream
(+5/0V) can modulate a carrier and be transmitted, demod at other end to
recover the formatted serial stream from the received carrier, and straight
into another UART to recover as 8 parallel bits.

Most UARTS should handle the upper limit of digital speed that a modulated
signal could cope with.

Chris.

 

[[email protected]]

He might want to add error-correction/detection - there are chips
around that will add a five bit checksum to the eight-bit data, which
will allow you to correct all single-bit errors, and detect many
multi-bit errors.

There is also the approach used in the Taxi chips, where eight-bt data
is recoded into the 256 ten-bit words that have lowrst DC content .....

 

[Anthony Fremont]

He might want to add error-correction/detection - there are chips
around that will add a five bit checksum to the eight-bit data, which
will allow you to correct all single-bit errors, and detect many
multi-bit errors.

Or you could just send it all twice (normal then inverted) and detect
virtually all errors.

There is also the approach used in the Taxi chips, where eight-bt data
is recoded into the 256 ten-bit words that have lowrst DC content

......

The method I mentioned above also helps to remove the DC especially if
you interlace the normal and inverted data bit by bit.

 

[Robert Lacoste]

If you plan to use "dumb" RF modules like FSK transmitters/receivers then an
UART will not be enough. You need :

- Some kind of preable sequence to let the receiver set its AGC

- Some kind of "start of frame" header
(these two point may not be necessary if you have a continuous transmission,
but this is often not autorized by regulatory agencies... at least in
Europe)

- Some way to balance the signal (as many "0" as "1"), and some way to
minimise the number of successive 0 or 1, if not the receiver will fail to
decode the signal. The "inverted/interleaved bit" mechanism proposed by
Anthony is a simple solution, but divide the throughput by two and may make
the identification of start bits more difficult. More robust solutions
exists (NRZ, etc).

- And very probably some error correction firmware.

As a starting point you may have a look at application notes published by
Chipcon (www.chipcon.com), in particular one named "RF radio modem" or
similar.

Of course everything is dependant on your requirements : how many errors can
you tolerate, what is the distance and power budget, what is the throughput,
etc.

Friendly yours,

--
Robert Lacoste
ALCIOM - The mixed signal experts
www.alciom.com

To contact us, thanks to click on the antispam link below :
http://www.cerbermail.com/?dCSHUxvwpw

 

[gwhite]

... but decoding that signal from the rx
side is getting really complicated...

LOL

 

[Luhan Monat]

I've got a 8-bit signal which I want to send over radio - which would
be received & decoded into the 8 bit signal - how do I do it???

I was thinking of taking the signals into a 1 bit shift register - but
decoding that signal from the rx side is getting really complicated...

any suggestions?

Yo,

Check out the units by Radiotronix. Just key the transmitter with
serial output and connect the reciever to a serial input. I have used
these with PIC's all the time.

http://members.cox.net/berniekm/Hot_Parts.html

 

[lemonjuice]

I've got a 8-bit signal which I want to send over radio - which would
be received & decoded into the 8 bit signal - how do I do it???

I was thinking of taking the signals into a 1 bit shift register - but
decoding that signal from the rx side is getting really complicated...

any suggestions?

No you don't need a shift register or IMO any flashy digital stuff to
send it by radio. I don't think you have in mind digital radio because
thats way too complicated. For normal analog radio here goes:
A trick you can use on the transmission side to reduce the chances
of detection errors on the receiver side is passing the binary bits
through a high pass filter. If you observe the waveforms on a scope
you'll see why ... The peaks on the outputs of your binary signals will
correspond to the 1's and the dips to the 0's but the peak to peak
voltage will be about double.

You don't seem to have any problems on the transmission side but if you
do we can go into that. So .....
Use a normal AM/FM transmitter to get your high pass filtered digital
signals transmitted

On the receiver get the demodulated amplified signal connect it to a
low pass filter with gain connected to 2 opamp buffers in parallel
then get the output connected to a flip flop like the 4093 and voilà
your digital signal.

The circuit is a bit more complicated then that with some math to do
but If you need more details let me know.