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PICList Thread
'2KHz pulse detection'
1996\10\21@205959 by Roger Coleman

picon face
Hello!

For those that want the background waffle, it follows below.

Otherwise, here is my query:

Is there an easy way to write code in the PIC to respond to a pulsed 2KHz input
and not one at any other frequency? The pulses are about 8 microseconds long and
happen about every 500 microseconds. I am receiving bursts of 2KHz signal that I
want to time the length of. Phase locked loops take to long to respond.

My current plan is to manually wait for a pulse to start, time it, wait for
another one, if another one starts within the acceptable bracket, it's a 2KHz
signal (ie a binary pulse has started). The end of the binary pulse would be
when the little pulses stop. This seems a bit clunky, so I thought I would try
the PICLIST out!

I have been a subscriber to the list for a couple of weeks now - it's great! My
vote is for all of the indirect PIC stuff to continue. Perhaps if people with
other, non PIC information included 'notPIC' in the subject it would help people
to have them auto deleted.

Thanks!

Here's the background:

I am building a bizarre communications system that flashes binary messages
across a room as an exhibit in a hands-on science museum. It uses ordinary
torches (with LED's instead of bulbs) as the transmitters and they flash really
slowly so that you can see the binary coding easily. On the other side of the
room is a de-coder that translates the binary codes back into messages. The
demonstration is to help illustrate what a digitally encoded binary message is.
The interactive bit is that you type in the message on a keyboard and watch as
it is transmitted. Each end of the room has a transmitter and receiver so that
you can send messages backwards and forwards. You can wave your hands in front
of the torches and garble the messages. It's great fun!

The neatest thing about it is that you can control the flash rate from about 1
bit / second to about 20 bits/ second to choose from being able to see the bits
and to transmit the message at a reasonable speed. The receiver automatically
adjusts to the modified transmission speed.

The whole thing is done with a 16C57 for transmitting and a 16C55 for receiving.
I'm using standard PC keyboards for the input of the messages and they are
displayed on 2x40 char LCD's. The display shows the binary code of each letter
as it is transmitted. I am really pleased with it!

Anyway, as you can imagine, I am using visible light and have all sorts of
problems with ambient lighting. I am using photodiodes positioned in the middle
of a couple of parabolic reflectors taken from torches and they work really well
(the distance is 10m), but I am unhappy with the arrangement since it is really
only a threashold light detector and it needs careful adjustment to get it set
up. If the sun comes out or someone turns all of the lights on, it gets messed
up. I have recently built in a comparator and an ambient light sensor to
compensate for this, but to make it rock solid I have also decided to transmit
the binary pulses using a 2KHz 'carrier' signal. Each binary pulse is actually a
2Khz flashing pulse, but you can't see it as that.

I look forward to hearing your comments!

Many Thanks,

Roger Coleman.

--

Roger Coleman,
Curator,
Guildford Discovery
Ward Street,
Guildford,
GU1 4LH
England

Tel/Fax +44 1483 37080
spam_OUT101722.3022TakeThisOuTspamcompuserve.com

1996\10\21@234413 by Steve Hardy

flavicon
face
> From: Roger Coleman <.....101722.3022KILLspamspam@spam@COMPUSERVE.COM>
:
>
> I am building a bizarre communications system that flashes binary messages
> across a room as an exhibit in a hands-on science museum. It uses ordinary
> torches (with LED's instead of bulbs) as the transmitters and they flash
really
> slowly so that you can see the binary coding easily. On the other side of the
> room is a de-coder that translates the binary codes back into messages. The
> demonstration is to help illustrate what a digitally encoded binary message
is.

My suggestion is to cheat a little bit.  Use standard IR transmit and
receive (i.e. IR LED modulated at 40KHz carrier).  This can be done in
parallel with the visible LED to give the hands-on touch.  No matter what
the bit rate is, you should limit the IR bursts to between 1 and 20ms,
since the IR receiver modules won't respond properly to really short or
long bursts.

If you insist on a purist approach, try using a high intensity LED e.g.
3 cd or more.  Failing that, a 1mW red laser diode should give heaps of signal
if you spread it just a little bit with a lens to avoid alignment problems.
Since it is monochromatic, you could also use a corresponding red filter
on the receiver end to make it more immune to ambient variations.

Note that laser diodes require the correct constant current driver otherwise
the (expensive) magic smoke can escape very easily.

Regards,
SJH
Canberra, Australia

1996\10\22@083328 by Mark A. Corio

picon face
In a message dated 96-10-21 22:59:59 EDT, you write:

>Anyway, as you can imagine, I am using visible light and have all sorts of
>problems with ambient lighting.

Roger,

I understand that you are using the visible light as part of the
demonstration, but you may be able to also use IR, etc..  In this case you
could have the visible light for demonstration without it actually being used
for transmission.  The IR (appropriately modulated) could be used for
transmission without it being visible.  This would be much less sensitive to
ambient conditions.

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850 --- Fax:  (716) 328-1144
http://www.frontiernet.net/~rmi/

***** Designing Electronics For Research & Industry *****

1996\10\22@083332 by Mark A. Corio

picon face
In a message dated 96-10-21 23:47:55 EDT, you write:

>If you insist on a purist approach, try using a high intensity LED e.g.
>3 cd or more.  Failing that, a 1mW red laser diode should give heaps of
>signal
>if you spread it just a little bit with a lens to avoid alignment problems.
>Since it is monochromatic, you could also use a corresponding red filter
>on the receiver end to make it more immune to ambient variations.
>
>Note that laser diodes require the correct constant current driver otherwise
>the (expensive) magic smoke can escape very easily.

You should also be aware that laser light is considered dangerous and is
controlled by government oversight.  You must stay within appropriate
regulations and even then you may be able to be sued by the idiot trying to
see what the inside of a laser looks like (now known as one-eye).

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850 --- Fax:  (716) 328-1144
http://www.frontiernet.net/~rmi/

***** Designing Electronics For Research & Industry *****

1996\10\22@175441 by Roger Coleman

picon face
Hello!

Thanks for the messages I have had about my communicator. I have experimented
with 3cd output 10mm LED's today and they are easily enough to beam across the
room.

The bit that I really need help on, however is the question of detecting the
2KHz input signal:

I need the software equivalent of a Phase locked loop, the output of which will
go high and low as the bursts of 2Khz signal start and stop. PLL IC's take too
long to lock on to the 2KHz signal.

My current plan is to time the distance between incoming pulses. This doesn't
seem very elegant, but is it the normal way of doing this sort of thing?

Thanks again,

Roger.

P.S. I got a message about my last message being too long. What is the limit?

--

Roger Coleman,
Curator,
Guildford Discovery
Ward Street,
Guildford,
GU1 4LH
England

Tel/Fax +44 1483 37080
101722.3022spamKILLspamcompuserve.com

1996\10\22@204501 by optoeng

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face
Mark A. Corio wrote:
{Quote hidden}

Using IR vs visible doesn't make too much difference wrt ambient
illumination.  In  fact, if the lighting is incandescent, the problem is
worse for IR.  You need to AC couple your preamplifier....better  yet,
use a bandpass amp.  Most data transmission via lightwaves uses much
higher carrier freq than 2 kHz to take advantage of the absence of light
noise at frequencies much above 1 kHz or so.  Red and IR filters are
easy to use and to obtain.  Email me if you want more details.

Anyhow, simple capacitive coupling between stages can work wonders.
--

Paul Mathews, consulting engineer
AEngineering Co.
.....optoengKILLspamspam.....whidbey.com
non-contact sensing and optoelectronics specialists

1996\10\22@205110 by Steve Hardy

flavicon
face
> From: "Mark A. Corio" <EraseMEMcoriospam_OUTspamTakeThisOuTaol.com>
>
> In a message dated 96-10-21 23:47:55 EDT, you write:
>
> >If you insist on a purist approach, try using a high intensity LED e.g.
> >3 cd or more.  Failing that, a 1mW red laser diode should give heaps of
> >signal
> >if you spread it just a little bit with a lens to avoid alignment problems.
> >Since it is monochromatic, you could also use a corresponding red filter
> >on the receiver end to make it more immune to ambient variations.
> >
> >Note that laser diodes require the correct constant current driver otherwise
> >the (expensive) magic smoke can escape very easily.
>
> You should also be aware that laser light is considered dangerous and is
> controlled by government oversight.  You must stay within appropriate
> regulations and even then you may be able to be sued by the idiot trying to
> see what the inside of a laser looks like (now known as one-eye).

Hardly! 1mW is below the level considered hazardous.  In any case, the
beam will be expanded by a lens so the radiation gathered by the pupil
will be a lot less than 1mW.  If you stick the appropriate laser class
sticker on it, then you are covered.  If I can get a 3mW laser pointer
with a label merely saying 'Caution: laser radiation / do not stare
into beam' then the poor bloke should be able to run his demo in a
controlled environment.

General gripe: it's a cryin' shame that the world is becoming dominated
by lawyers and doctors and other nay-sayers.  Australia seems to be
shouldering some of that litigious weight that the US is buckling
under, where morons are able to turn plain bad luck (with a healthy
dose of their own stupidity) into mountains of gold (all at taxpayers'
expense).  I mean some of the payouts are just ridiculous!  Rant rant
rave rave...

Regards,
SJH
Canberra, Australia

1996\10\22@225739 by John Payson

picon face
> The bit that I really need help on, however is the question of detecting the
> 2KHz input signal:
>
> I need the software equivalent of a Phase locked loop, the output of which
will
> go high and low as the bursts of 2Khz signal start and stop. PLL IC's take too
> long to lock on to the 2KHz signal.
>
> My current plan is to time the distance between incoming pulses. This doesn't
> seem very elegant, but is it the normal way of doing this sort of thing?

I think your best bet would be to design a filter/oscillator whose resonant
frequency is 2KHz but whose "Q" is low enough that it will ring but not
sustain oscillation; a tunable LC circuit might be good.  In this way, any
trace of a 2KHz signal will cause the device to sustain oscillation--even in
the presence of other noise--but other frequencies won't have such an effect.

Alternatively, you could use a 4051 and four caps to build a switched-cap
filter which you could then drive with the PIC.  If you go this route, I'd
suggest wiring it as follows:

4051 pins:
 A,B : Wire to two PIC port pins
 1x: Wire to photo-receiver through large-value resistor; also wire
     the 1x pin directly to the "+" input of a comparator
 1y: Wire to the "-" input of the comparator
 0x,2y: Wire to .1uF cap [other leg of cap to ground]
 1x,3y: [ditto, using another cap]
 2x,0y: [ditto, using another cap]
 3x,1y: [ditto, using another cap]

The PIC should cycle the A,B pins through the four values with a total
cycle rate of 2KHz [i.e. change them 8,000 times/second].  If a signal
is present, the comparator should consistently show a hit for some [AB]
combination (e.g. the comparator may return 010011001110111001000100)
                                            ~   ~   ~   ~   ~   ~
This approach would combine digital accuracy with analog sensitivity (you
may wish to bias the comparators a little bit; if a real signal is present
it should show up fairly strongly on the capacitors).

1996\10\23@003805 by optoeng

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face
Roger Coleman wrote:
>
> Hello!
>
> Thanks for the messages I have had about my communicator. I have experimented
> with 3cd output 10mm LED's today and they are easily enough to beam across the
> room.
>
> The bit that I really need help on, however is the question of detecting the
> 2KHz input signal:
>
> I need the software equivalent of a Phase locked loop, the output of which
will
{Quote hidden}

A good way to do demodulation such as you require is to use a 'matched
filter', which is a convolution filter where the 'template' has the
temporal shape of the expected input signal.  I'll describe it
abstractly first, then give the outline of a micrcomputer
implementation.

Formally, you multiply the incoming signal with the template and
accumulate a sum, the vector dot-product.  If this sum is large and
positive, your input and template match in frequency and phase.  If the
sum is large and negative, they match in frequency but are 180 deg out
of phase.  Square waves present a particularly easy situation: you can
represent 1 of a square wave's 2 levels with +1 (i.e., adding) and the
other level with -1 (subtracting).  Depending on how sophisticated is
your demodulator, the input signal can be quantized to 1 or more bits.
You need to sample at least twice per cycle for at least 1 cycle, and
more sampling is called 'oversampling'.  Oversampling has 2 benefits:
you can overcome 'aliasing', which is the filter's susceptibility to
pass multiples of the basic frequency (harmonics), and you can determine
when to 'trigger' the correlation process (read on).

Elaborate versions of the matched filter technique involve continuous
digitization of the input, along with convolving the template.  This
approach will find signals deeply buried in massive amounts of noise.
If your signal is strong enough, it's much simpler to threshold the
amplified input signal (use a comparator to convert to a string of 1s
and 0s) and use the first positive edge to the trigger the simple
demodulation process described below.

Simple discriminator for 2kHz:
0. clear register 'w' and detect flag bit 'b'
1. On first signal positive-going edge, begin to execute the following
loop:

       a. for 250us, if input = high then increment w
                     if input = low then decrement w
       b. for 250us, if input = high then deccrement w
                     if input = low then increment w
       c. compare value of w to discrimination threshold constant T
               if w >= T then
                       set b TRUE
                       clear w
       d. if b = TRUE then goto step a
          else goto step 0

There are many variations on this approach.  The value of T, by the way,
depends on how much oversampling you can manage.  For example, if you
can only check the input once each 250us, then the max value for W at
step c will be 2, and you'd best set T = 2.  If you can check the input
8 times each 250us, then w can reach 16, and you can set T at some
lesser value if you want to experiment with trading off sensitivity and
error rate.  The process as described can run on interrupts, and your
application can simply check the value of b at any time.

--

Paul Mathews, consulting engineer
AEngineering Co.
@spam@optoengKILLspamspamwhidbey.com
non-contact sensing and optoelectronics specialists

1996\10\23@082904 by Mark A. Corio

picon face
In a message dated 96-10-22 23:49:00 EDT, you write:

>Hardly! 1mW is below the level considered hazardous.  In any case, the
>beam will be expanded by a lens so the radiation gathered by the pupil
>will be a lot less than 1mW.  If you stick the appropriate laser class
>sticker on it, then you are covered.  If I can get a 3mW laser pointer
>with a label merely saying 'Caution: laser radiation / do not stare
>into beam' then the poor bloke should be able to run his demo in a
>controlled environment.
>
>General gripe: it's a cryin' shame that the world is becoming dominated
>by lawyers and doctors and other nay-sayers.  Australia seems to be
>shouldering some of that litigious weight that the US is buckling
>under, where morons are able to turn plain bad luck (with a healthy
>dose of their own stupidity) into mountains of gold (all at taxpayers'
>expense).  I mean some of the payouts are just ridiculous!  Rant rant
>rave rave...

My comment was intended to point out this problem...I agree with you.
Let's sue the lawyers for this.....oh, sorry...I was momentarily a victim of
the US mentality to shurk responsibility.  I thought that the US was the only
place with this problem....well, so much for the grass being greener
elsewhere.

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850 --- Fax:  (716) 328-1144
http://www.frontiernet.net/~rmi/

***** Designing Electronics For Research & Industry *****

1996\10\23@082908 by Mark A. Corio

picon face
In a message dated 96-10-22 21:51:25 EDT, you write:

>Using IR vs visible doesn't make too much difference wrt ambient
>illumination.  In  fact, if the lighting is incandescent, the problem is
>worse for IR.  You need to AC couple your preamplifier....better  yet,
>use a bandpass amp.  Most data transmission via lightwaves uses much
>higher carrier freq than 2 kHz to take advantage of the absence of light
>noise at frequencies much above 1 kHz or so.  Red and IR filters are
>easy to use and to obtain.  Email me if you want more details.

I agree with Paul here that the ambient noise is similar at both visible and
IR wavelengths.  My suggestion was based on being able to use the commercial
IR transmitters and recievers which have the higher frequency
modulation/demodulation functions built in.  These devices use higher
frequencies (~40KHz I think) to avoid lower frequency interferences form
lighting, etc..  It should be noted that flourescent lighting (used in most
commercial/public buildings) emits frequencies over 40KHz and these need to
be filtered out if a low signal level is to be detected.

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850 --- Fax:  (716) 328-1144
http://www.frontiernet.net/~rmi/

***** Designing Electronics For Research & Industry *****

1996\10\23@093148 by myke predko

flavicon
face
>Hello!
>
>Thanks for the messages I have had about my communicator. I have experimented
>with 3cd output 10mm LED's today and they are easily enough to beam across the
>room.
>
>The bit that I really need help on, however is the question of detecting the
>2KHz input signal:
>
>I need the software equivalent of a Phase locked loop, the output of which will
>go high and low as the bursts of 2Khz signal start and stop. PLL IC's take too
>long to lock on to the 2KHz signal.

Roger,

Reading all this makes me wonder, why don't you use something like a TV
remote control (ie 3x KHz or 40 KHz modulated I/R Signal) and just have a
visible light LED for "show" (ie put in parallal with the I/R one)?

With this hardware, you'd get exactly the same effect, but in terms of
hardware it would be *very* simple (just an LED that sends a square wave at
the modulating frequency (ie too fast for the human eye to see the turning
on/off of the LED) and the receiver would just be a I/R receiver (many
brands available).  A PIC (with a 40 KHz TMR0 Interrupt frequency would be
perfect for this).

>
>My current plan is to time the distance between incoming pulses. This doesn't
>seem very elegant, but is it the normal way of doing this sort of thing?
>

I think what you're looking at here is "Manchester Encoding" which sends a
synching pulse and then the time to the next synching pulse is the data (ie
short is a "0", long is a "1").  This is actually how most I/R receivers work.

>Thanks again,

I've probably got some code I can give you that would help you out with this
stuff.  If it sounds like something that you want to do, give me a ding,

Myke

Avoiding precedents does not mean nothing should ever be done.  It only
means that nothing should ever be done for the first time - Sir Humphrey
Appleby K.C.B.

1996\10\23@210431 by Scott Dattalo

face
flavicon
face
Paul Mathews wrote:

... The correct way to detect a 2kHz square wave. However, Paul
don't forget the quadrature waveform! It's possible that the incoming
signal and the square wave you're beating it against  (i.e. multiplying)
are 90 degrees out of phase. In which case the dot product is zero.

I've been looking at this fairly closely in the last couple of weeks
and I've come up with a VERY SIMPLE algorithm that will perform the
filtering Paul describes. It also takes care of the quadrature waveform
too. I originally was going to post the theory too, but it's too long
for the current PIC List temperament. Those of you who enjoy the
theoretical enlightenment then drop me a line.



If you have seen the theory then.....
Finally, all of the above can be combined to create the following
(UNTESTED) code. It takes 15 cycles/sample regardless of the path
that the code takes (recall the recent "Isochronous Code" thread).

TONE_FREQ       EQU     2000  ;Hz
SAMPLING_TIME   EQU     15    ;uS
RESOLUTION      EQU     2<<13 ;8192
DPH             EQU     SAMPLING_TIME*TONE_FREQ*RESOLUTION/1000000
Qbit_c          EQU     13-8  ;Bit 5
Qbit_s          EQU     12-8  ;Bit 4

start:
       MOVLW   NUM_OF_SAMPLES
       MOVWF   samples
samp_loop:
       MOVLW   DPH
       ADDWF   ph_lo,F       ;Low byte of phase
       SKPNC
        INCF   ph_hi,F

       BTFSS   INPUT_PORT,INPUT_BIT
        goto   low

   ;Input is high
       BTFSC   ref_wave,Qbit_c ;
        INCF   DFT,F           ;c=1,s=x,in=1
       nop
       goto    next

low:
   ;Input is low
       BTFSS   ref_wave,Qbit_c ;
        goto   $-2
       BTFSS   ref_wave,Qbit_s
        INCF   DFT_s,F         ;c=1,s=0,in=0
       nop
next
   ;Put a delay loop here if your crystal frequency>4Mhz

       DECFSZ  samples,F
         goto  samp_loop


   ;At this point the variable "DFT" has the sum of both
   ;quadratures. We can decide/experiment with thresholds
   ;to see  how well they correlate to actual signal.
   ;
   ;  Do  some more system stuff...

       goto     start


Scott

PS The theory behind this is almost identical to the
theory behind the DTMF decoding.

1996\10\24@024433 by nigelg

flavicon
picon face
In message  <KILLspam961022215144_101722.3022_IHN181-2KILLspamspamCompuServe.COM>> RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU writes:

> My current plan is to time the distance between incoming pulses. This doesn't
> seem very elegant, but is it the normal way of doing this sort of thing?

Sometimes!, Sharp Electronics curent products use this method for their
IR remote controls. Bursts of IR are transmitted and the data is dependent
on the gaps between them, I can't remember the figures off hand, but it
was something like 0.5mS is a '1' and 1mS is a '0'. The complete code is
sent twice, with the second version having part of the code inverted, this
is then compared to the first code received for error detection.

If you are interested, I have working code for receiving and decoding these
Sharp IR signals.

A more popular scheme is the Philips RC5 system, this uses the transition
from high/low and low/high to signify the two bit states.

For your requirements, I suspect the Sharp type method may be more visually
interesting, as the differing bits can easily be seen.

Nigel.

         /----------------------------------------------------------\
         | Nigel Goodwin   | Internet : spamBeGonenigelgspamBeGonespamlpilsley.demon.co.uk |
         | Lower Pilsley   | Web Page : http://www.lpilsley.demon.co.uk    |
         | Chesterfield    |                                        |
         | England         |                                        |
         \----------------------------------------------------------/

1996\10\24@110819 by &Ltwouter Suverkropp

picon face
Transmitter: simple oscillator (use gates) driving IR LED at 38.4KHz (39 will
do)
for show add visible LED that is always on

Receiver: Use integrated receiver (Maplin, RS, Farnell, about 2.5 quid)
Pull up output, hey presto!

Sorry, no PIC needed.

Wouter

1996\10\24@123132 by optoeng
flavicon
face
Scott Dattalo wrote:
{Quote hidden}

I'm glad that I started things off....however, note that the algorithm I
sketched out (admittedly sketchy and non-optimal) has starting edge
detection, so I don't understand your point about the quadrature wave.
Upon calculating a dot product of zero, the process restarts.

I've implemented more sophisticated versions of this algorithm in many
ways: beginning in 1978 using 9601 monostable multivibrators, in 1980
using custom ASICs, in 1982 using microcontrollers, in 1992 using PGA,
etc., so I'm quite confident that it works.
--

Paul Mathews, consulting engineer
AEngineering Co.
TakeThisOuToptoengEraseMEspamspam_OUTwhidbey.com
non-contact sensing and optoelectronics specialists

1996\10\24@175625 by Scott Dattalo

face
flavicon
face
Paul Mathews wrote:
>
> I'm glad that I started things off....

I'm glad you did too.

>                                       however, note that the algorithm I
> sketched out (admittedly sketchy and non-optimal) has starting edge
> detection, so I don't understand your point about the quadrature wave.
> Upon calculating a dot product of zero, the process restarts.

My apologies, I glossed right over that detail. The algorithm I discuss
is really better suited for tracking several frequencies simultaneously.
(Like in DTMF decoding). In which case, the "filter" is running
continuously
and is NOT synchronizing itself to the data. Consequently, the filter
is dealing with a random initial phase of the input signal.

Furthermore the quadrature waveform stuff is really a theoretical
artifact.
If you look closely (but not too closely... because there's a bug) at
the
routine I posted you'll see that the 'quadrature waveform' is easily
derived from the 'non-quadrature waveform'.

> I've implemented more sophisticated versions of this algorithm in many
> ways: beginning in 1978 using 9601 monostable multivibrators, in 1980
> using custom ASICs, in 1982 using microcontrollers, in 1992 using PGA,
> etc., so I'm quite confident that it works.

I'm confident it works too.

Scott

PS. The bug in the routine I posted earlier is that the variable named
'ref_wave' should have been 'ph_hi'. My apologies.

1996\10\24@213552 by Tom Messenger

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Scott Dattalo wrote:


>I've been looking at this fairly closely in the last couple of weeks
>I originally was going to post the theory too, but it's too long
>for the current PIC List temperament. Those of you who enjoy the
>theoretical enlightenment then drop me a line.


For me, I'd rather see the theory than the code. Codeing is the easy part;
figuring out what to code is usually what we get paid for. Thanks!

Tom Messenger // RemoveMEkristspamTakeThisOuTthegrid.net

1996\10\25@021232 by tjaart

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Scott Dattalo wrote:
{Quote hidden}

I simulated a GPS spread spectrum locking mechanism with a similar
algorithm in a post-grad subject on MATLAB. If it can track 24 codes
with 1023 bits long, 2kHz will be no problem. It works well even with
the code buried way below the antenna noise level.
--
Friendly Regards

Tjaart van der Walt
______________________________________________________________
|  Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
|           +27-(0)11-622-8686 | http://wasp.co.za             |
|______________________________________________________________|

1996\10\28@064349 by Juan Jose Abba

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>Scott Dattalo wrote:
>
>
>>I've been looking at this fairly closely in the last couple of weeks
>>I originally was going to post the theory too, but it's too long
>>for the current PIC List temperament. Those of you who enjoy the
>>theoretical enlightenment then drop me a line.




Scott, pls leat us have the theory.  For me it is more important than the code.
thanks in advance
juan

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