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PICList Thread
'Telemetry encoding'
2000\06\12@183131 by Dr. Chris Kirtley

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Dear all,

I'm planning  to use a 16F84 to take data from four sensors and output
them to a miniature RF telemetry unit (Linx LC418). The latter is
carrier wave modulated, so I'll need to digitally encode the data. Has
anyone out there done this? If so can you give me any tips - e.g. what
encoders are available. Do I even need one if I have a PIC? Space is at
a premium!

TIA!

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: spam_OUTkirtleyTakeThisOuTspamcua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
Send subscribe/unsubscribe to .....listprocKILLspamspam@spam@info.curtin.edu.au

2000\06\12@190858 by Robert.Rolf

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Just bit bang your data out as if it were a serial port.
Using standard async formatting (1 start, 8 data, 1 stop) you can
easily capture the data on a PC via it's serial port and a terminal
program. Pick a standard baud rate that the Linx can handle.
Remember that you'll want to HAVE carrier for a mark condition so that
you'll know when you're out of range and you start getting overrun
errors
on the incoming data.

"Dr. Chris Kirtley" wrote:
>
> Dear all,
>
> I'm planning  to use a 16F84 to take data from four sensors and output
> them to a miniature RF telemetry unit (Linx LC418). The latter is
> carrier wave modulated, so I'll need to digitally encode the data. Has
> anyone out there done this? If so can you give me any tips - e.g. what
> encoders are available. Do I even need one if I have a PIC? Space is at
> a premium!

Have you considered the brute force method (KISS)? Depending on your
data
rate requirements this might be easier and smaller.
A SMT 4060 + 4051 and a 4046 let you do audio FM telemetry.
For each time slice you connect your sensor, and it changes the
frequency
of the VCO used to modulate your radio link. You recover the FM with
another
4046 and then A/D the result at your PC (sound card could do it too but
more PC side software required). You set aside one slice to be higher
that max (or lower) sensor and use that to sync the recovery process.

In my case I modulated the FM transmitter directly, but because I was
scanning at 10kHz I could get away with just using the key pulse as a
clamp reference for the other DC coupled signals.

There are many ways to skin this cat, depending on your data rates,
resolution requirements, reliability issues, size/power constraints.
The 4051/4046 is going to draw a LOT less power than your PIC (and
choose
the lowest PIC clock rate you can to save power (and choose a nice
baud rate number to make your software easier. 1.8432Mhz is nice).

Hope this helps get you started.
Robert.RolfspamKILLspamUAlberta.ca

2000\06\13@101640 by pandersn

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Dr. Chris....

It would seem to me that you could form up your own data packets within the
PIC and then send those packets (frames) to a centeral gathering or server
site - be it feet or miles away. Depends, of course, on your RF power - and
I'm assuming it is slow.

Packet radio uses frames similar to X25 frames: [header, addressing, data,
check sum.] This way, the server can check on the integrity of the data.
You can obtain a copy of the AX25 spec (Amateur Packet-Radio Link Layer
Protocol, Version 2.-0, Oct. 1984) from the ARRL, 860-666-1541.

Other block frame protocols also exist. See most digital communications
texts.

Phil

If you wanted to test this idea without coding first, buy a KPC-3+ pair or
radio modems from AES Milwauke or HRO Anaheim. I was a part of the KPC-3+
design team.



On Monday, June 12, 2000 8:30 PM, Dr. Chris Kirtley [SMTP:.....kirtleyKILLspamspam.....CUA.EDU]
wrote:
{Quote hidden}

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