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'[PIC] 38KHz from 12f675 TMR0 interrupt?'
2005\05\03@190237 by Tom Wrighton

picon face

Hello All,


I’m a newbie, hobbyist, nonprofessional and retired.  I make these

declarations up front so you might take my query with a grain of salt.

I’m still working on my 1st PIC project, though at this point I feel I have

learned a lot (for me anyway). I bought a PICkit-1 after seeing it at one of

our robot club meetings.  As many of you know it comes equipped with a

12F675.  I have become obsessed with using it for my project idea, and also

to program it with assembly language.  My project is to make a small IR

beacon as part of a robotic competition for navigation.  I would like to

execute a small flashing LED countdown (one pulse each for 5 seconds)

and than modulate an IR LED for 20 seconds.  I think I have the TMR0

interrupt figured out and I can execute seconds timing and LED flashing.

My confusion comes in as follows:  I’m trying to use the internal RC osc

(  _INTRC_OSC_NOCLKOUT  ) which I believe ends up at 1 us

execution cycles.  To achieve a 38KHz flash rate I need an interrupt every

26.3 us.  This calculates to loading the TMR0 with something like

decimal 242 +/- 4 cycles for a half cycle at 38KHz.  This does not leave me

very many cycles left for the ISR.  At this point I have tried to measure the

frequency of the flashing LED with a Craftsman DMM that has a freq

measurement capability.  The best I can do so far is 32 and a fraction KHz.

At this point I am wondering if I need to use a crystal osc. And run it at

10 MHz instead of the 4Mhz of the internal?  I have followed the PICLIST

for several months and am very impressed with the expertise and graciousness

of the membership.  Up front: any and all comments and guidance you might

offer will be greatly appreciated.


Best Regards and Thank You,


Tom Wrighton

Crystal Lake, IL, USA



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2005\05\03@194457 by Jinx

face picon face
> cycles.  To achieve a 38KHz flash rate I need an interrupt every
> 26.3 us.  This calculates to loading the TMR0 with something like
> decimal 242 +/- 4 cycles for a half cycle at 38KHz.  This does not
> leave me very many cycles left for the ISR

Hi Tom, I imagine something like this for a simple LED flash and
1 sec counter

wait  goto wait   ;wait for TMR0 IRQ

isr  clear TMR0 IF flag
     reload TMR0 with half-cycle time
     toggle LED pin
     increment 76000 half cycles count
     skip if 76000 reached
     retfie        ;back to wait
     recognise and reset 76000 count
     retfie

You could bump Fosc up to 20MHz if you do need more ICs for
processing other tasks, but for this the 4MHz IntRC would be OK
To get as close to 38kHz as possible you'd need to work out a
pattern of reloads with 242 and 243 that will average out to 38kHz,
although most receivers have a fairly tolerant bandwidth (at the
expense of reducing range)

Have a look here for some other notes about timers

http://www.piclist.com/techref/microchip/timer.htm

2005\05\03@194557 by PicDude

flavicon
face
26us will give you ~38.5khz which works well with a 38khz IR receiver module, though I expect the range may not be as great as if you get 26.3khz.  I currently do this in a calculated loop (not in the ISR), but my app is a keyfob transmitter with only a few different signals.  If you plan to do much more in the PIC, you will probably need to run it at a higher frequency.

Cheers,
-Neil.


On Tuesday 03 May 2005 06:02 pm, Tom Wrighton scribbled:
{Quote hidden}

2005\05\03@201133 by PicDude

flavicon
face
On Tuesday 03 May 2005 06:44 pm, PicDude scribbled:
> 26us will give you ~38.5khz which works well with a 38khz IR receiver
> module, though I expect the range may not be as great as if you get
> 26.3khz.  I currently do this in a calculated loop (not in the ISR), but my

Oops -- meant 26.3us (not khz).


{Quote hidden}

2005\05\03@212431 by Spehro Pefhany

picon face
At 04:02 PM 5/3/2005 -0700, you wrote:

>My confusion comes in as follows:  I'm trying to use the internal RC osc
>
>(  _INTRC_OSC_NOCLKOUT  ) which I believe ends up at 1 us
>
>execution cycles.  To achieve a 38KHz flash rate I need an interrupt every
>
>26.3 us.

13.15usec per half cycle.  I don't think you have enough
time to save and restore context and reload timer0 at 4MHz, let alone
keep track of other timing.

If you run the PIC from a 10/20MHz resonator you'll get a more accurate signal
(because a typical resonator is +/-0.5% guaranteed) and you'll get a
resolution of 200ns (and, crucially, a lot more cycles to play with for
each interrupt). If you use 33/66 cycles for each half-cycle, the error
will be -.3% (not counting oscillator error), which doesn't sound too bad.

At 4MHz, you should be able to get it to work by writing it as an
isochronous loop rather than using interrupts, but it will severely limit
what else you can get the PIC to do at the same time, and how you have
to do it.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2005\05\03@231202 by Jinx

face picon face
> 13.15usec per half cycle.  I don't think you have enough time to
> save and restore context and reload timer0 at 4MHz, let alone
> keep track of other timing.

You could be right - as a straight 38kHz generator it would work
but what's going to make it a tight squeeze at 4MHz is the testing
and branching

Maybe put a 32kHz xtal on Timer1 and use that to measure the
5 & 20 second intervals (T1 OSC available only if you use the
internal osc), keeping TMR0 @ 4MHz just for the 38kHz

Or even WDT + a timer ?

OK OK, run it at 10MHz ;-)

BTW Tom, I'd recommend ZTX transistors for driving IR LEDs.
They switch faster and better and more current than other common
types (eg TO92 like BCxxx or 2Nxxxx). Their higher current rating
means a low value series R can be used eg 1 or 2 ohms for good
range, but watch the wattage dissipated by the IR LED

2005\05\04@000858 by Tom Wrighton

picon face
Neil, Jinx & Spehro,

Thanks for the response.  I was suspicious that I might have to use
a resonator and run it at 10MHz or so.  Thanks for the reference links,
and I' ll see if I can pin down the reference to ZTX transistors.  I've been
playing around with this thing for weeks and I think the saturation exposure
I've been giving myself is working.  I'm actually starting to feel comfortable
with what I'm doing.  Now I just need to get a few parts and see if I can
make some more progress.  Again, thanks for the help.

Best regards,

Tom



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2005\05\04@003623 by Denny Esterline

picon face
I'm no expert on IR links, but the ones I've used had much lower than 50%
duty cycles.
It seems to me, that if you used a shorter on time, it'd make the looping
and testing easier,
not to mention letting you drive the LED harder.

Either way, it'll be a tight fit.
-Denny



{Original Message removed}

2005\05\04@005503 by Byron A Jeff

face picon face
On Tue, May 03, 2005 at 04:02:36PM -0700, Tom Wrighton wrote:

> Hello All,

Welcome Tom.

> I'm a newbie, hobbyist, nonprofessional and retired.  I make these
> declarations up front so you might take my query with a grain of salt.

Must be nice. Hope you are enjoying it.

> I?m still working on my 1st PIC project, though at this point I feel I have
> learned a lot (for me anyway). I bought a PICkit-1 after seeing it at one of
> our robot club meetings.  As many of you know it comes equipped with a
> 12F675.  I have become obsessed with using it for my project idea, and also
> to program it with assembly language.

Both the part and the language could be problematic if you're obsessed with
it.

> [Snip of the issue. To much to do, not enough time. ]

> The best I can do so far is 32 and a fraction KHz.
> At this point I am wondering if I need to use a crystal osc. And run it at
> 10 MHz instead of the 4Mhz of the internal?  I have followed the PICLIST
> for several months and am very impressed with the expertise and
> graciousness of the membership.

Well that's certainly kind of you. Using the crystal could help, and losing
the two I/O pins won't kill your project in this case.

>  Up front: any and all comments and guidance you might
> offer will be greatly appreciated.

Well back to the obsession thing. I've been pointing out to members on this
list that using hardware can simplify the life of beginners. And I'm always
told that it's too complex.

Your case is a perfect example. The PWM module on other PIC chips are the
perfect set and forget tool required to get your job done. A 16F88 would
solve the job easily with just a simple setup of the periperal.

A quick poke around the pickit description doesn't point to any parts that
has PWM built it.

Finally on the language thing. Learn enough assembly so that you can
communicate ideas with others in it. Then consider higher level languages
simply because they facilitate setting up things faster.

Good luck on your project. And remember that PIC hardware periperals such
as the USARTS, PWM/CCP, ADC/comparators, and the timers really are your
friends.

BAJ

2005\05\04@014504 by Russell McMahon

face
flavicon
face
> BTW Tom, I'd recommend ZTX transistors for driving IR LEDs.
> They switch faster and better and more current than other common
> types (eg TO92 like BCxxx or 2Nxxxx). Their higher current rating
> means a low value series R can be used eg 1 or 2 ohms for good
> range, but watch the wattage dissipated by the IR LED

Jinx has got a bit religious over Zetex transistors over time. That
said, they do make some very nice products. Do take car to read the
data sheet very carefully to ensure you are really getting what you
expected.

They make some of the nicest small moderate power transistors around.
Their E-line package is TO92 size but has far better thermal
characteristics. Good for a watt in free air as I recall. They have
some E-Line transistors with simultaneous ratings of 1A, current gain
in the hundreds and commendable Vsat (tenths of a volt range). You pay
quite a  premium price for these.

If you want small transistors for switching moderate power that are
not quite as good as Zetex's best, but still far better than most and
far cheaper, look at BC337 / BC327. 500 mA (or slightly more for some
makers). Beta in the hundreds (depending on current) and OK Vsat. Can
be 10 or 20 times cheaper than top Zetex parts. Pd not as good.


       RM

2005\05\04@015534 by Tom Wrighton

picon face
Denny & Byron,

Thanks very much for the response.  I understand that I am probably
setting myself up with a handicap by using the 12f675, but that is
what I have so I'm trying it out first.  I fully intend to explore many of
the other features of the different PICs and I have all the time in the
world, so I'm taking them one-at-a-time.  Since I'm in a robotics club
(http://www.chibots.org) I will be getting into PWM for motor control soon.
After I get this project operating I intend to try another (different) PIC.
Another response I got suggested using a ZTX transistor to drive the
IR LED.  I believe that to be Australian or European.  Does anyone
know what would be a good substitute available here in the states.
Once I get comfortable with assembly, I will probably swing over to
a version of 'C' which I used to do career wise about fifteen years ago.
Of course there will be a significant relearning process but I look forward
to it.  I had better not drag this out.  Again thanks for the response and
looking forward to communicating on the list more in the future.

Best Regards,

Tom

Byron A Jeff <.....byronKILLspamspam@spam@cc.gatech.edu> wrote:
On Tue, May 03, 2005 at 04:02:36PM -0700, Tom Wrighton wrote:

> Hello All,

Welcome Tom.

> I'm a newbie, hobbyist, nonprofessional and retired. I make these
> declarations up front so you might take my query with a grain of salt.

Must be nice. Hope you are enjoying it.

> I?m still working on my 1st PIC project, though at this point I feel I have
> learned a lot (for me anyway). I bought a PICkit-1 after seeing it at one of
> our robot club meetings. As many of you know it comes equipped with a
> 12F675. I have become obsessed with using it for my project idea, and also
> to program it with assembly language.

Both the part and the language could be problematic if you're obsessed with
it.

> [Snip of the issue. To much to do, not enough time. ]

> The best I can do so far is 32 and a fraction KHz.
> At this point I am wondering if I need to use a crystal osc. And run it at
> 10 MHz instead of the 4MHz of the internal? I have followed the PICLIST
> for several months and am very impressed with the expertise and
> graciousness of the membership.

Well that's certainly kind of you. Using the crystal could help, and losing
the two I/O pins won't kill your project in this case.

> Up front: any and all comments and guidance you might
> offer will be greatly appreciated.

Well back to the obsession thing. I've been pointing out to members on this
list that using hardware can simplify the life of beginners. And I'm always
told that it's too complex.

Your case is a perfect example. The PWM module on other PIC chips are the
perfect set and forget tool required to get your job done. A 16F88 would
solve the job easily with just a simple setup of the peripheral.

A quick poke around the pickit description doesn't point to any parts that
has PWM built it.

Finally on the language thing. Learn enough assembly so that you can
communicate ideas with others in it. Then consider higher level languages
simply because they facilitate setting up things faster.

Good luck on your project. And remember that PIC hardware peripherals such
as the USARTS, PWM/CCP, ADC/comparators, and the timers really are your
friends.

BAJ

2005\05\04@024256 by Wouter van Ooijen

face picon face
> execute a small flashing LED countdown (one pulse each for 5 seconds)
> and than modulate an IR LED for 20 seconds.  I think I have the TMR0
> interrupt figured out and I can execute seconds timing and
> LED flashing.

Are you deliberately making trouble for yourself? If not: forget
interrupts for this project.

When you say 'modulate the IR LED for 20 seconds': if you use standard
IR receivers you must insert gaps in the tranmission, otherwise you will
saturate the receivers.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\05\04@053444 by Jinx

face picon face
> When you say 'modulate the IR LED for 20 seconds': if you use
> standard IR receivers you must insert gaps in the tranmission,
> otherwise you will saturate the receivers

The common IS1U60 doesn't suffer from that IME. I use them in
door minders with unbroken (except by legs and people looking
for contact lenses) 38kHz IR beams

http://www.hvwtech.com/pages/products_view.asp?ProductID=166

I noticed recently that a low-power IR sensor like this (300uA IIRC,
about 1/10th of the IS1U60) is now on the market. I forget details

2005\05\04@053631 by Jinx

face picon face
.
> Another response I got suggested using a ZTX transistor to drive the
> IR LED.  I believe that to be Australian or European.  Does anyone
> know what would be a good substitute available here in the states.

www.zetex.com/9.0/9-1-1a.asp?areaid=2&countryid=223&country=United+St
ates

2005\05\04@063112 by Wouter van Ooijen

face picon face
> > When you say 'modulate the IR LED for 20 seconds': if you use
> > standard IR receivers you must insert gaps in the tranmission,
> > otherwise you will saturate the receivers
>
> The common IS1U60 doesn't suffer from that IME. I use them in
> door minders with unbroken (except by legs and people looking
> for contact lenses) 38kHz IR beams
>

The datasheet is not very clear about this, but is does state a maximum
'high' time (800us) and a minimum 'low' time (400us). But the block
circuit does not show an AVR feedback like the TSOP's, so maybe it is
indeed different in this respect. Or just a sloppy datasheet...

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\05\04@070941 by Jinx

face picon face
> The datasheet is not very clear about this, but is does state a
> maximum 'high' time (800us) and a minimum 'low' time (400us).
> But the block circuit does not show an AVR feedback like the
> TSOP's, so maybe it is indeed different in this respect. Or just
> a sloppy datasheet...

If you were going to make a "universal" transmitter that could be
received by any receiver, it probably would be wise to modulate
the carrier with a data packet or tone, eg 1kHz

2005\05\04@071156 by olin_piclist

face picon face
Tom Wrighton wrote:
> I'm a newbie, hobbyist, nonprofessional and retired.

OK, but you can still write your posts single spaced.  Your double spaced
post was annoying to read since it effectively shrunk my screen window by 2.

> I'm trying to use the internal RC osc
>
> (  _INTRC_OSC_NOCLKOUT  ) which I believe ends up at 1 us
>
> execution cycles.

Yes.

> To achieve a 38KHz flash rate I need an interrupt
> every
>
> 26.3 us.  This calculates to loading the TMR0 with something like

There are several ways to do this.  Taking an interrupt every half cycle is
probably not the best.  I've driven IR LEDs at 40KHz with similar chips, and
did the timing in line.  Shut off interupts and count cycles.  With a little
assembler math, you can have it insert the right numbers of NOPs at the
right places for you.

Another possibility is to use timer 0 but with software polling.  This gives
you 3 cycles of jitter, which you can eliminate with a short jump table into
a string of NOPs.  Or not.  Maybe some jitter is acceptable.

Here is some code that runs on a 10F202 that uses software polling and
de-jittering of timer 0 for each half cycle:

;***********************************************************************
;
;   Subroutine IR_ON
;
;   Emit infrared output via the infrared LEDs for the next REG0 carrier
;   pulses.  The carrier pulse is emitted a consistant delay after timer
;   0 wraps from 255 to 0.  Timer 0 is adjusted so that it will next wrap
;   one IR carrier cycle later.
;
;   REG0 is trashed.
;
ir_on
iron_loop                    ;back here each new carrier pulse
        btfsc   tmr0, 7     ;wait for timer 0 wrap
        goto    $-1
;
;   TMR0 is now either 2, 3, or 4, depending on where within the wait loop
;   timer 0 wrapped from 255 to 0.  The add to PCL here removes this jitter.
;
        movf    tmr0, w     ;get either 3, 4, or 5
        addwf   pcl
        nop
        nop
        nop
        nop                 ;3
        nop                 ;4
;
;   An IR carrier cycle starts right now.  Instruction timing jitter has
;   been removed.
;
ir_swon                      ;IR emitter switched on here
        bsf     ir_pin      ;turn on the IR emitter
        movlw   irt0inc
        addwf   tmr0        ;update timer 0 for next carrier cycle start
ii       set     $ - ir_swon ;make number of cycles emitter on so far
 if ii > ironcy
        error   IR emitter on for too many cycles
   endif
        waitnop ironcy - ii ;fill in cycles until switch of IR emitter
        bcf     ir_pin      ;turn off the IR emitter

        decfsz  reg0        ;count one less IR carrier pulse left to emit
        jump    iron_loop   ;back to do next pulse
        retlw   0           ;done with all requested pulses


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\04@072131 by olin_piclist

face picon face
Denny Esterline wrote:
> I'm no expert on IR links, but the ones I've used had much lower than
> 50% duty cycles.
> It seems to me, that if you used a shorter on time, it'd make the
> looping and testing easier,
> not to mention letting you drive the LED harder.

Less than 50% duty cycle is often used in battery operated equipment to save
power.  It does *not* allow you to get more range for the same power, in
fact it is a little less efficient.  Assuming the LED will always be driven
full on and full off, 50% square wave puts the largest fraction of the input
power at the fundamental.  Any deviation from 50% increases power into the
harmonics relative to the fundamental.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\04@082415 by Mike Harrison

flavicon
face
On Wed, 4 May 2005 07:21:24 -0400, you wrote:

>Denny Esterline wrote:
>> I'm no expert on IR links, but the ones I've used had much lower than
>> 50% duty cycles.
>> It seems to me, that if you used a shorter on time, it'd make the
>> looping and testing easier,
>> not to mention letting you drive the LED harder.
>
>Less than 50% duty cycle is often used in battery operated equipment to save
>power.  It does *not* allow you to get more range for the same power, in
>fact it is a little less efficient.  

But range in an IR system is mostly about peak, not avarage power, assuming the receiver has
reasonable frequency response, so shorter, more powerful pulses will give substantially more range.
Shorter duty cycle also allows the LED to be run harder - many IR LED datasheets quote seperate
figures for avarage and peak currents.
IR remotes typically use duty cycles below 20%,  putting 100-500ma pulses into the LED.

IRDA is an extreme example, using very short duty cycles with high-bandwidth receivers to get
maximum range.

2005\05\04@112801 by Spehro Pefhany

picon face
At 10:55 PM 5/3/2005 -0700, you wrote:
>Denny & Byron,
>
>Thanks very much for the response.  I understand that I am probably
>setting myself up with a handicap by using the 12f675, but that is
>what I have so I'm trying it out first.

Okay, by going for one interrupt per cycle, I think it can be made
to work.


isr:movwf       w_temp                          ; save context
   swapf        STATUS,W
   bcf          STATUS,RP0
   bsf          GPIO,0                          ; bring pin high
   movwf        status_temp
   incf counter,F                       ; used by background program for
timing
   bcf          INTCON,2                        ; clear timer interrupt flag
   nop
   nop
   nop
   nop
   nop
   nop
   movlw        .250
   bsf          GPIO,0                          ; bring pin low
   movwf        TMR0
   swapf        status_temp,W                   ; restore context
   movwf        STATUS
   swapf        w_temp,F
   swapf        w_temp,W
   retfie

In simulation, it gives about 37.7kHz at 44% or so duty cycle with a 4MHz
clock.
(remember to 'calibrate' the internal oscillator in your code)
The background routine runs like a 60kHz or so PIC, so very slow,
but not insane. If you eliminate some of the nops above you'll
get faster background operation but less duty cycle. If you're driving
the LED directly you might want to swap bsf and bcf and sink current,
because the PIC is better at sinking current.

The 'counter' byte rolls over every 6.78ms or so, and can be used
to control your slower timing in the background routine. You would
detect the rollover by looking at the msb of counter. That would
allow several hundred instructions to execute in each background
loop before you'd miss a rollover. A single byte in the background
routine could time up to 1.7 seconds or so.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2005\05\04@120944 by Mark Rages

face picon face
On 5/4/05, Tom Wrighton <.....ckn1ghtKILLspamspam.....yahoo.com> wrote:
> Your case is a perfect example. The PWM module on other PIC chips are the
> perfect set and forget tool required to get your job done. A 16F88 would
> solve the job easily with just a simple setup of the peripheral.
>
> A quick poke around the pickit description doesn't point to any parts that
> has PWM built it.

What about the 12F683?

Regards,
Mark
EraseMEmarkragesspam_OUTspamTakeThisOuTgmail.com

The Pickit supports the following parts:
- PIC10F 200*, 202*, 204*, 206*
- PIC12F508, 509, 510
- PIC16F54*, 57*, 59*
- PIC16F505
- PIC12F629, 635, 675, 683
- PIC16F630, 636, 676, 684, 688, 785, 916, 917
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\05\04@124444 by phil B

picon face
Actually, the 675 (or its cheaper brother the 629 or
even cheaper cousin the 509) is perfectly fine for the
task you described.  I would not bother using the
timer or interrupts.  Just code the 38K generation in
a timed loop.  You can get 1/2 clock (2 Fosc)
resolution by using n clocks high and n-1 clocks low.
You can further tweak Fosc by playing with the osccal
value.  The good news is that most IR receivers are
pretty forgiving of the exact frequency - most spec
sheets I've seen show a couple of khz range centered
around the frequency (38K in your case).

Depending on your IR LED, you may be able to drive it
directly from the PIC.  I'd go up to 20 mA.  Use a pin
per LED if you need more than one.  

Of course, I'd be remiss if I didn't point out that a
simple 555 timer would make an excellent beacon
generator with a couple of Rs and Cs and can drive a
lot more LED current.  But then what's the fun of
that?


--- Tom Wrighton <ckn1ghtspamspam_OUTyahoo.com> wrote:
{Quote hidden}

> --

2005\05\04@140701 by Tom Wrighton

picon face
Thank You Everyone,

I've received lots of good (understandable to a newbie)
guidance and tips in response to my query and I
appreciate it very much.  I like the snippets of code,
in that with what I've learned already I can understand
and follow them quite easily.  Thanks!

1........1.........2.........3.........4.........5.........6.........7..

Olin,
Sorry about taking up so much of your monitor.
I must admit I was cautioned once before to try
and keep my text to under 72 characters per line.
It's a bit hard to remember when I'm typing single
lines and returning before wrap-around.  I don't fully
understand but this is under 72 and occupies about
52% of the line capability on my monitor.  I will try
to accommodate everybody in the future.
Again, thanks to all of you for your help and tips.

Best Regards,

Tom




               
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2005\05\04@145135 by Tom Wrighton

picon face
Hi All,

In light of the large positive response I received to my
query, I thought I would give you a little more detail on
my objective.  Our club (http://www.chibots.org) is looking
to prod interest by possibly developing 1 or 2 new
competitions over and above the standards that we
have going now.  ie. line following, advanced line
following, solarollers and minisumo.  I lit on the idea
of providing a short duration (20 seconds) IR beacon
for a robot to get a bearing on and then try to navigate
to it.  The beacon would be on just long enough to get
the bearing and than turn off.  The robot must than
navigate to the beacon in reasonable time.  The
shortest time would be the better navigator.  This
would give our club members the opportunity to build
there skills and knowledge in dead reckoning, location
determination and object avoidance.  The line-o-sight
from starting point to beacon would be clear enough
to take a bearing, but not clear enough for passage.
I have to admit that this follows along with my interest
in robotics (autonomous navigation).  I hope this little
note wasn't contrary to the guidelines of the PICLIST.

Best Regards to All,

Tom


               
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2005\05\04@145822 by olin_piclist

face picon face
Tom Wrighton wrote:
> Sorry about taking up so much of your monitor.
> I must admit I was cautioned once before to try
> and keep my text to under 72 characters per line.

That wasn't the problem.  Your lines were double spaced for some reason.  In
other words, there was a blank line between each line that contained text.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\04@154018 by Dwayne Reid

flavicon
face
At 09:11 PM 5/3/2005, Jinx wrote:
> > 13.15usec per half cycle.  I don't think you have enough time to
> > save and restore context and reload timer0 at 4MHz, let alone
> > keep track of other timing.
>
>Maybe put a 32kHz xtal on Timer1 and use that to measure the
>5 & 20 second intervals (T1 OSC available only if you use the
>internal osc), keeping TMR0 @ 4MHz just for the 38kHz

Close - so close.

How about putting a 38KHz crystal on TMR1, then turn it on and off as
needed?  Those 38 KHz crystals are darned cheap - even from Digikey - and
you have all the other resources of the '675 available for use.

dwayne

--
Dwayne Reid   <KILLspamdwaynerKILLspamspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2005\05\04@162544 by Byron A Jeff

face picon face
On Wed, May 04, 2005 at 11:09:44AM -0500, Mark Rages wrote:
> On 5/4/05, Tom Wrighton <RemoveMEckn1ghtTakeThisOuTspamyahoo.com> wrote:
> > Your case is a perfect example. The PWM module on other PIC chips are the
> > perfect set and forget tool required to get your job done. A 16F88 would
> > solve the job easily with just a simple setup of the peripheral.
> >
> > A quick poke around the pickit description doesn't point to any parts that
> > has PWM built it.
>
> What about the 12F683?

Hence the quick poke. The 12F683 would be the winner hands down in the 8 pin
category.

BAJ

2005\05\04@163141 by Jan-Erik Soderholm

face picon face
Tom Wrighton wrote :

> Hi All,
>

[snipped project info...]

> I hope this little
> note wasn't contrary to the guidelines of the PICLIST.
>  
> Best Regards to All,
>  
> Tom

He he...
Providing some project background or overview is what's
usualy *missing* from many questions to the list. It usualy
helps a lot to have the full picture to be able to give the
"right" answer.

IMHO there is absolutly no problem with that "note"...

Best Regards and good luck !
Jan-Erik.



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