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'[EE:] IR modulator schematic?'
2004\01\20@024024 by ?q?Debbie=20Hynes?=

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PICers - i'm looking round for ideas to build an IR modulator cct. did a quick
google but mostly fopund IR receivers.

I'm using a 16f84 to drive an IR led but i'll need to modulate it at 38kbps. i
guess i could use a 555 to gate the LED on/off - any other ideas?

thankz 4 advice

best - Debbie :)

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2004\01\20@031631 by Robert Rolf

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74HC14 wired as R/C osc. With  diodes in the feedback path you can set
whatever duty cycle you like. 555 has the advantage of being able to
drive the LED directly (300mA output spec on the Signetics part IMS).
555's are also more stable w.r.t. temperature. 555C + vfet is lower
power solution.

Debbie Hynes wrote:
>
> PICers - i'm looking round for ideas to build an IR modulator cct. did a quick
> google but mostly fopund IR receivers.
>
> I'm using a 16f84 to drive an IR led but i'll need to modulate it at 38kbps. i
> guess i could use a 555 to gate the LED on/off - any other ideas?
>
> thankz 4 advice

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2004\01\20@031632 by Jinx

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> 16f84 to drive an IR led but i'll need to modulate it at 38kbps

A 555 example

http://home.clear.net.nz/pages/joecolquitt/txless.html

or set up a 38kHz PWM output and turn it on/off.

I recommend Zetex transistors for the LED switching. They're
heaps better than common junk-box transistors (eg 2N2222,
BC548, BC337 etc)

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2004\01\20@050231 by Mike Harrison

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On Tue, 20 Jan 2004 18:39:56 +1100, you wrote:

>PICers - i'm looking round for ideas to build an IR modulator cct. did a quick
>google but mostly fopund IR receivers.
>
>I'm using a 16f84 to drive an IR led but i'll need to modulate it at 38kbps. i
>guess i could use a 555 to gate the LED on/off - any other ideas?

Why not use the PIC to modulate it?

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2004\01\20@064359 by Anand Dhuru

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As Mike suggests, you could do this without adding any extra hardware. If
you could use the 16F628 instead, set the hardware PWM to 36 KHz; drive the
IR LED between your data pin (cathode), and the PWM out (anode). This would
take up 2 pins on your PIC, but you could do it with just one pin as well if
you control the PWM output itself as per your data.

Regards,

Anand


{Original Message removed}

2004\01\20@074118 by Olin Lathrop

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Debbie Hynes wrote:
> PICers - i'm looking round for ideas to build an IR modulator cct.
> did a quick google but mostly fopund IR receivers.
>
> I'm using a 16f84 to drive an IR led but i'll need to modulate it at
> 38kbps. i guess i could use a 555 to gate the LED on/off - any other
> ideas?

First, ditch the 16F84.  It's obsolete.

You can have the PIC produce the complete IR signal, carrier and modulation,
if it's got nothing else to do at the time.  I used a 16F630 in a high
volume product to do just that.  It was running off its own internal 4MHz
oscillator.  Worked very well.


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2004\01\20@074324 by Olin Lathrop

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Jinx wrote:
> I recommend Zetex transistors for the LED switching. They're
> heaps better than common junk-box transistors (eg 2N2222,
> BC548, BC337 etc)

Why?  An IR led is typically driven with 50-100mA.  I don't see why that
should be a problem for a junkbox transistor, like the 2N4401 I use for such
purposes.


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2004\01\20@074946 by hael Rigby-Jones

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>-----Original Message-----
>From: Olin Lathrop [@spam@olin_piclistKILLspamspamEMBEDINC.COM]
>Sent: 20 January 2004 12:42
>To: KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
>Subject: Re: [EE:] IR modulator schematic?
>
>
>Jinx wrote:
>> I recommend Zetex transistors for the LED switching. They're heaps
>> better than common junk-box transistors (eg 2N2222, BC548, BC337 etc)
>
>Why?  An IR led is typically driven with 50-100mA.  I don't
>see why that should be a problem for a junkbox transistor,
>like the 2N4401 I use for such purposes.

They are better in a couple of respects:  They have a surprisingly high gain
at high collector currents, which means you aren't wasted power driving the
base hard.  They also have a very low Vcesat compared to average signal
transistors, which may be important if you have a remote running from e.g.
3volts.  They also come in the tiny (for a leaded component) E-line package
which may be good news if space is tight.

The downside (as always) is cost and to a lesser extent availability.

Regards

Mike




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2004\01\20@081719 by Mike Harrison

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On Tue, 20 Jan 2004 07:42:06 -0500, you wrote:

>Jinx wrote:
>> I recommend Zetex transistors for the LED switching. They're
>> heaps better than common junk-box transistors (eg 2N2222,
>> BC548, BC337 etc)
>
>Why?  An IR led is typically driven with 50-100mA.  I don't see why that
>should be a problem for a junkbox transistor, like the 2N4401 I use for such
>purposes.

For long-range applications, peak LED currents of the order of 500-2000mA are not uncommon. The
Zetex parts are good at doing this sort of thing with sensible base current, although you can also
get cheap SOT-23 MOSFETS that are often better for this type of use.  
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2004\01\20@142729 by ?q?Debbie=20Hynes?=

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Thankz 4 the tips everybody! Hmmm ... good ideas all round, both 555, 74HC14 or
use the PIC. pity 'bout the ol'F84 being obsolete - my fav processor.

i'll have a fiddle with programming a PWM o/p & see how i go.
thankz again - Debbie :)

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2004\01\20@171937 by Jinx

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> Thankz 4 the tips everybody! Hmmm ... good ideas all round, both
> 555, 74HC14 or use the PIC. pity 'bout the ol'F84 being obsolete -
> my fav processor

I'd call it "superceded" rather than "obsolete" (which seems to have
an emotional or judgemental connotation). The F84 is still widely
available at any sales level and probably will be for some time. It's
still a perfectly good micro after all for a lot of applications. Don't
many Smart Cards use the F84 ?

But personally I don't use it for new designs because it's not as
sophisticated as newer PICs, and is relatively expensive

Oh, and good luck with your project

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2004\01\20@173404 by Olin Lathrop

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Jinx wrote:
> Don't many Smart Cards use the F84 ?

No, only dumb cards.

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2004\01\20@183100 by Andrew Warren

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Debbie Hynes <RemoveMEPICLISTEraseMEspamEraseMEmitvma.mit.edu> wrote:

> pity 'bout the ol'F84 being obsolete - my fav processor.

   When Olin says the 16F84 is obsolete, all he really means is that
   he doesn't use it.  There are other PICs that may cost less
   and/or have more features, but the 16F84 is still in production
   and isn't going away any time soon.

> i'll have a fiddle with programming a PWM o/p & see how i go.

   Here's a bit of code that may help; it assumes that your PIC is
   running at 4 MHz.

   As as often the case with code I post to the list, this has
   neither been tested nor even assembled... But this isn't exactly
   rocket science, so I'd be surprised if it didn't work:

               LIST R=DEC

       COUNT   EQU     [ANY REGISTER]
       MS      EQU     [ANOTHER REGISTER]

       TOGGLE  EQU     00000001B       ;ALL ZEROES, WITH A SINGLE
                                       ;"1" IN THE POSITION THAT
                                       ; CORRESPONDS TO THE LED
                                       ;(THIS EXAMPLE ASSUMES
                                       ;THAT THE LED IS ON RB0).

       ; SEND A MODULATED (38 KHZ) PULSE.  ENTER WITH THE LED
       ; OFF, AND WITH W HOLDING THE DESIRED LENGTH OF THE
       ; PULSE IN MILLISECONDS; EXITS WITH LED OFF.  ASSUMES
       ; THAT THE LED IS ON PORTB AND IS HIGH-TRUE.

       PULSE:
               MOVWF   MS

       OUTER:
               MOVLW   76
               MOVWF   COUNT

               MOVLW   TOGGLE

       INNER:
               XORWF   PORTB

               NOP
               GOTO    $+1
               GOTO    $+1
               GOTO    $+1
               GOTO    $+1

               DECFSZ  COUNT
               GOTO    INNER

               NOP

               XORWF   PORTB

               GOTO    $+1
               GOTO    $+1
               GOTO    $+1

               DECFSZ  MS
               GOTO    OUTER

               GOTO    $+1     ;THESE THREE LINES AREN'T REALLY
               GOTO    $+1     ;NECESSARY; YOU CAN SAFELY DELETE
               NOP             ;THEM.

               BCF     LED

               RETURN

   Good luck...

   -Andy

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2004\01\20@183721 by Jinx

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> > Don't many Smart Cards use the F84 ?
>
> No, only dumb cards.

Touche

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2004\01\20@183931 by Olin Lathrop

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Andrew Warren wrote:
> When Olin says the 16F84 is obsolete, all he really means is that
> he doesn't use it.

And that it's a bad idea to use one in a new design.  I agree, there are
lots of old design out there using the 16F84, so it's not likely to go out
of production soon.


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2004\01\20@185251 by Andrew Warren

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Olin Lathrop <PICLISTSTOPspamspamspam_OUTmitvma.mit.edu> wrote:

> > When Olin says the 16F84 is obsolete, all he really means
> > is that he doesn't use it.
>
> And that it's a bad idea to use one in a new design.

   When Olin says that it's a bad idea to use the 16F84 in a new
   design, all he really means is that he doesn't use the 16F84 in
   his new designs.

   -Andy

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2004\01\20@185912 by Herbert Graf

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> Debbie Hynes <EraseMEPICLISTspamEraseMEmitvma.mit.edu> wrote:
>
> > pity 'bout the ol'F84 being obsolete - my fav processor.
>
>     When Olin says the 16F84 is obsolete, all he really means is that
>     he doesn't use it.  There are other PICs that may cost less
>     and/or have more features, but the 16F84 is still in production
>     and isn't going away any time soon.

       Just because something is still made doesn't mean it's not obsolete. 386
processors were made for YEARS after they were considered obsolete, in fact
they are STILL being made in one form or another.

       The 84, along with the 54, is obsolete, in every respect of it's meaning.
Just because something is obsolete does not mean it's not useful in certain
circumstances. TTYL

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2004\01\20@190948 by steve

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>     When Olin says the 16F84 is obsolete, all he really means is that
>     he doesn't use it.

Olin prefers to use parts that don't run at the rated speed or simply don't
exist yet.

Steve.

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2004\01\20@191609 by Russell McMahon

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> > > When Olin says the 16F84 is obsolete, all he really means
> > > is that he doesn't use it.

That's a tad unfair.
The 16F84 is more expensive and less capable than newer PICs that are plug
in replacements electrically.
It makes little sense to use it for new designs UNLESS you have a very
specific reason for doing so. In the case covered by this thread one factor
(regardless of what you think about its merit) was  that the 84 is less
likely to confuse beginners.

Perhaps a better term than obsolete would be obsolescent.


       Russell McMahon

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2004\01\20@194802 by Mike Harrison

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On Tue, 20 Jan 2004 18:58:42 -0500, you wrote:

>> Debbie Hynes <TakeThisOuTPICLIST.....spamTakeThisOuTmitvma.mit.edu> wrote:
>>
>> > pity 'bout the ol'F84 being obsolete - my fav processor.
>>
>>     When Olin says the 16F84 is obsolete, all he really means is that
>>     he doesn't use it.  There are other PICs that may cost less
>>     and/or have more features, but the 16F84 is still in production
>>     and isn't going away any time soon.
>
>        Just because something is still made doesn't mean it's not obsolete. 386
>processors were made for YEARS after they were considered obsolete, in fact
>they are STILL being made in one form or another.
>
>        The 84, along with the 54, is obsolete, in every respect of it's meaning.
>Just because something is obsolete does not mean it's not useful in certain
>circumstances. TTYL

Actually the 54 is not obsolete in all respects, as its C revision is still marginally cheaper than
any other 18 pin PIC.  
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2004\01\20@195423 by Herbert Graf

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> Actually the 54 is not obsolete in all respects, as its C
> revision is still marginally cheaper than
> any other 18 pin PIC.

       Just because something is cheaper doesn't make it NOT obsolete. I'm willing
to bet an 8088 is cheaper then a AMD64, yet it's still VERY obsolete.

       It seems, for one reason or another, people are forgetting what obsolete
ACTUALLY means in it's use.

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2004\01\20@202029 by Jinx

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> It seems, for one reason or another, people are forgetting what
> obsolete ACTUALLY means in its use

Well, there are two dictionary meanings for "obsolete" that you
could cite

1. No longer in use, discarded

2. Out-of-date, old-fashioned

1. doesn't apply to the F84. It's in production and well-used

2. is subjective and, if you consider 1. as true, then it doesn't
apply either really

"obsolescence" doesn't fit either - there is no sign of the F84
being on its way out. In fact the F628 is ahead in the queue to
the guillotine than the F84

I think this simply comes down to personal opinion which, at
the end of the day, the F84s and Microchip couldn't give a
rat's a** about. They're still a good earner

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2004\01\21@041721 by ?q?Debbie=20Hynes?=

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Crikey guys!! i didn't mean 2 start a Great Debate like this! :))
I agree the 84 looks a little dated but it still gets the job done. i'm gonna
use it 4 this proj cuz i'm still learning the f877. the f84 is simple and fast
2 do a quick project on, however ... so if it works, use it, hey?

in the meantime, i'll adapt that excellent 555 design till i get the hang of
using a PIC to generate 38kHz bursts. i captured the waveforms from the
handheld r/c and i have Wagner's notes on Sony protocols so halfway there
already?? ;)
Best - Debbie


--- Jinx <spamBeGonejoecolquitt@spam@spamspam_OUTCLEAR.NET.NZ> wrote: > > It seems, for one reason or
another, people are forgetting what
{Quote hidden}

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2004\01\21@043902 by

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Debbie Hynes wrote :

> in the meantime, i'll adapt that excellent 555 design till
> i get the hang of using a PIC to generate 38kHz bursts.

Well that's *realy* easy.

I just setup the PWM module to produce the basic
36/38/whatever carrier. I then just flipped a bit somewhere
(I don't recal right now, could have been the TRIS bit...)
to enable/disable the PWM module.
Simple as that. When disabling/enabling the PWM, I synced
to the TMR2 overflow flag, so I always got a nice clean
carrier out without any half-cycles. The timing of the bits
was done in the TMR2 overflow ISR. Just counting up and
enabling/disabling when appropriate. 98% of the time the
PIC was just idling and waiting for the hardware do the work...

Now, since you insist on using that ol' F84, you might
have to do it the hard way...

Jan-Erik.

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2004\01\21@044528 by Jinx

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> Crikey guys!! i didn't mean 2 start a Great Debate like this! :))

's ok - boys will be boys y'know

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2004\01\21@050224 by William Chops Westfield

face picon face
On Wednesday, Jan 21, 2004, at 01:17 US/Pacific, Debbie Hynes wrote:

> the f84 is simple and fast
> 2 do a quick project on, however ... so if it works, use it, hey?
>
the main thing leading to the "obsolete" tag is that the 16F84 is
twice to three times as expensive as newer parts that are proper
supersets (more memory, more features.)  IFF you have a nearby
supplier who sells the parts in appropriate quantities.  It does
you no good to know that a 16F628 is $3 from digikey if you got
all your other parts from jameco and aren't likely to get up to
the minimum order size where a $3 part isn't overwhelmed by postage
and/or minimum order/handling charge issues.  I've noticed that a
fair number of the "hobbyist" suppliers haven't jumped on the "F84"
is obsolete bandwagon - presumably they still have stock they ordered
a long time ago, and/or for all those existing projects that use it.

The situation changes pretty drastically if you're in a financial
position to frequently order $100 worth of parts at a time...
("16F628s go from $3 to $1.73 if I buy 25?  Sure, I'll do that!")

BillW

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2004\01\21@055943 by Wouter van Ooijen

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> When Olin says the 16F84 is obsolete, all he really means is that
> he doesn't use it.

But when I say it is obsolete I mean: if you buy from me please buy
16F84A, at twice the price of a 16F628A or three times the price of a
16F630!

Wouter van Ooijen

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2004\01\21@074848 by Byron A Jeff

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On Wed, Jan 21, 2004 at 08:17:03PM +1100, Debbie Hynes wrote:
> Crikey guys!! i didn't mean 2 start a Great Debate like this! :))

Debbie,

You didn't start this debate. It's be on going for two or three years now. I
summarized most of the relevant points on my 16F84 is obsolete page:

http://www.finitesite.com/d3jsys/16F628.html

> I agree the 84 looks a little dated but it still gets the job done. i'm gonna
> use it 4 this proj cuz i'm still learning the f877. the f84 is simple and fast
> 2 do a quick project on, however ... so if it works, use it, hey?

Well here's the issue. You are correct... to a point. The 16F84 does get the
job done. However because of its limitations you have to change your
programming mindset in order to work around those limitations. Software bit
banged UARTS, software PWM, external hardware comparators and A/D, and
virtual software timers because of a lack of real timers are just the tip of
the iceberg. In fact your original project of discussion is a perfect example
to illustrate the point. To wit...

>
> in the meantime, i'll adapt that excellent 555 design till i get the hang of
> using a PIC to generate 38kHz bursts.

The opportunity to figure it out will be lost. If you are hobbyist, like many of
us, most of your projects are one offs. That means that once it works there's
little advantage to go back and redo the project after it's working.

And I'm not sure that's really the point. The real bottom line is that if you
had a newer chip in hand, it's advantageous to take advantage of the "set and
forget" periperals that are available. That's why you're going to gate a 555.
Once the 555 is set to the proper frequency and duty cycle, you no longer have
to devote code space or timing to track that signal. The newer PICs PWM
module is the same: set it up once, then forget about it in your code. It makes
your designs simpler to implement, smaller from a code space perspective and
more robust becuse there's less to debug.

So think about a 16F628A, or a 16F819, or the catch all 16F88 the next time.

BAJ

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2004\01\21@075056 by Olin Lathrop

face picon face
Andrew Warren wrote:
> When Olin says that it's a bad idea to use the 16F84 in a new
> design, all he really means is that he doesn't use the 16F84 in
> his new designs.

No Andrew, that's not all I mean.  You seem to be trolling for a pissing
contest.  I would have just ignored this comment except that I don't want
anyone who isn't so familiar with the PIC product line to be lead astray.

The 16F628 does more, costs less, and has the same footprint as the 16F84.
The 16F628 has double the program memory, from 1K to 2K words.  Now there is
the 16F648A which is the same thing with 4K words, and still costs
considerably less than the 'F84 or 'F84A.

If you can do with a few less pins, the 16F630 is a good alternative.  It
has the same code space as the 'F84, 4 less pins, and is a LOT cheaper.
Some of the pins that had dedicated functions on the 'F84 can be reused as
I/O pins on the 'F630.  If you are using the internal oscillator and don't
need MCLR, then the 'F630 only has one less useable pin.

If you don't want to take my word for it, a look at the Microchip line card
shows the 16F84 is a "mature" product.  Even Microchip is telling you not to
use it in new designs.

For reference, here are the budgetary prices listed on the Microchip web
site:

 16F630    $1.20
 16F628    $1.61
 16F648A   $1.70
  16F84A   $3.42
  16F84    $4.39

I stand by my statement that using the 16F84 in a new design is a bad idea.
In fact, it's downright silly.


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

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2004\01\21@123726 by Andrew Warren

flavicon
face
Olin Lathrop <RemoveMEPICLIST@spam@spamspamBeGonemitvma.mit.edu> wrote:

> > When Olin says that it's a bad idea to use the 16F84 in a new
> > design, all he really means is that he doesn't use the 16F84
> > in his new designs.
>
> No Andrew, that's not all I mean.

   Clearly.  When you tell someone it's a bad idea to use a certain
   part, you also mean that you know what all of his or her unstated
   requirements are.  You know, for instance, his level of familiarity
   with all the PICs, his schedule, his projected volume, his inventory,
   his budget, the capabilities of his development tools, etc.

   Right?

> You seem to be trolling for a pissing contest.

   Not at all.  I'm pointing out that blanket pronouncements like "It's
   a bad idea to use the 16F84 in a new design" or "It's a bad idea to
   use MPASM's absolute mode" are silly.

   Debbie wants to quickly build what sounds like a one-off project.
   She HAS 16F84s, she KNOWS the 16F84, all of her tools apparently
   SUPPORT the 16F84, Microchip still MAKES the 16F84... Why, again, is
   it necessary for her to push back her schedule while she acquires and
   learns how to use a different part and its tools?

> I would have just ignored this comment except that I don't want anyone
> who isn't so familiar with the PIC product line to be lead astray.

   Here's one way to do that while still sounding reasonable:

       "If you use the 16F84, you'll have to write the IR-transmitter
       code using carefully-timed software delays, which can be a pain.
       Here's [code/a code description/my contact info and hourly
       rate/whatever].

       "If you don't NEED to use the 16F84, you may want to look at
       [some other PIC]. It's cheaper and better [in all these ways],
       and its built-in PWM generator can make your task really easy."

> The 16F628 does more, costs less, and has the same footprint as the
> 16F84.

   I said as much in an earlier message.  As you know, though, "does
   more and costs less" is hardly the only criterion for selecting a
   microcontroller.

   -Andy

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2004\01\21@155921 by ?q?Debbie=20Hynes?=

flavicon
face
--- Byron A Jeff <.....byronRemoveMEspamCC.GATECH.EDU> wrote: > On Wed, Jan 21, 2004 at
08:17:03PM +1100, Debbie Hynes wrote:
> > Crikey guys!! i didn't mean 2 start a Great Debate like this! :))
>
> Debbie,
>
> You didn't start this debate. It's be on going for two or three years now. I
> summarized most of the relevant points on my 16F84 is obsolete page:

We'll all be obsolete by then? :(
>
>
> The real bottom line is that if you
> had a newer chip in hand, it's advantageous to take advantage of the
"set..... SNIP ...
>
> So think about a 16F628A, or a 16F819, or the catch all 16F88 the next time.
>
Good point BAJ. i have a 16f877 dev kit but haven't figured out the modules
yet. on it, as they say. the proj is still on protoboard so a quick changeover
is no problem,

thankz - Debbie :)

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