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'[OT]: Blinking LED softly....'
2001\06\05@204522 by John Pearson

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How can I soften the blinking of an LED so that it doesn't go on and off so abruptly? Is there a way of doing this with just an RC and no transistor?

I am blinking an LED with a pic port and I can use either high or low to light LED.

Thanks

John

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2001\06\05@205338 by Tony Nixon

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John Pearson wrote:
>
> How can I soften the blinking of an LED so that it doesn't go on and off so abruptly? Is there a way of doing this with just an RC and no transistor?
>
> I am blinking an LED with a pic port and I can use either high or low to light LED.
>
> Thanks
>
> John

Use Pulse Width Modulation as it comes on and goes off.
Coming on, start with a narrow pulse and gradually widen it until it is
fully on.
Going off, gradually narrow the pulse until it is completely off.

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2001\06\05@205719 by Bob Ammerman

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>How can I soften the blinking of an LED so that it doesn't go on and off so
>abruptly? Is there a way of doing this with just an RC and no transistor?

No C needed.

Just blink it with assembly language PWM.  ;-)

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\06\05@213213 by John Pearson

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Dang, I knew I left out a very important parameter: My pic clock speed is
240Hz. I don't think this has a software solution.


{Original Message removed}

2001\06\05@215305 by Andrew Warren

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John Pearson <EraseMEPICLISTspam_OUTspamTakeThisOuTmitvma.mit.edu> wrote:

> Dang, I knew I left out a very important parameter: My pic clock speed
> is 240Hz. I don't think this has a software solution.

John:

You could try it anyway.  25% and 75% might look awful, but 33, 50,
and 66 could be ok...

   BSF     LED     ;25% duty-cycle for 8/60 second.
   BCF     LED     ;
   GOTO    $+1     ;
   BSF     LED     ;
   BCF     LED     ;
   GOTO    $+1     ;

   BSF     LED     ;33% duty-cycle for 9/60 second.
   BCF     LED     ;
   NOP             ;
   BSF     LED     ;
   BCF     LED     ;
   NOP             ;
   BSF     LED     ;
   BCF     LED     ;
   NOP             ;

   BSF     LED     ;50% duty-cycle for 8/60 second.
   BCF     LED     ;
   BSF     LED     ;
   BCF     LED     ;
   BSF     LED     ;
   BCF     LED     ;
   BSF     LED     ;
   BCF     LED     ;

   BSF     LED     ;66% duty-cycle for 9/60 second.
   NOP             ;
   BCF     LED     ;
   BSF     LED     ;
   NOP             ;
   BCF     LED     ;
   BSF     LED     ;
   NOP             ;
   BCF     LED     ;

   BSF     LED     ;75% duty-cycle for 8/60 second.
   GOTO    $+1     ;
   BCF     LED     ;
   BSF     LED     ;
   GOTO    $+1     ;
   BCF     LED     ;

   BSF     LED     ;ON.

-Andy


=== Andrew Warren --- aiwspamspam_OUTcypress.com
=== IPD Systems Engineering, CYSD
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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2001\06\05@220251 by Spehro Pefhany

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At 06:29 PM 6/5/01 -0700, you wrote:
>Dang, I knew I left out a very important parameter: My pic clock speed is
>240Hz. I don't think this has a software solution.

You could probably inline a handful of instructions that would give you the
appearance of a soft on/off. If you assume  0.25 second is soft enough,
that gives you 15 instructions, with a granularity of 16.7msec.

Something like:

       bsf     PORTA,0
       bcf     PORTA,0
       nop
       nop
       nop
       bsf     PORTA,0
       bcf     PORTA,0
       bsf     PORTA,0
       bcf     PORTA,0
       bsf     PORTA,0
       nop
       nop
       bcf     PORTA,0
       bsf     PORTA,0

You may have to fiddle with this a bit to get the appearance to be
acceptable.

Best regards,
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2001\06\05@222118 by Dale Botkin

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On Tue, 5 Jun 2001, John Pearson wrote:

> How can I soften the blinking of an LED so that it doesn't go on and
> off so abruptly? Is there a way of doing this with just an RC and no
> transistor?
>
> I am blinking an LED with a pic port and I can use either high or low
> to light LED.

Are you driving the LED directly from the PIC pin with a resistor?  How
about a cap in parallel with the LED, with a current limiting resistor
between Vdd and the LED?  I haven't tried this, may or may not work.

Dale
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A train stops at a train station.  A bus stops at a bus station.
On my desk I have a workstation...

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2001\06\05@225519 by Spehro Pefhany
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At 09:22 PM 6/5/01 -0500, you wrote:

>
>Are you driving the LED directly from the PIC pin with a resistor?  How
>about a cap in parallel with the LED, with a current limiting resistor
>between Vdd and the LED?  I haven't tried this, may or may not work.

It would work better with a "T" network (2 series resistors, parallel
capacitor), and even better with an additional R across the LED, but
the basic problem with this approach is that the
capacitor gets beefy pretty fast. *IF* you use a super-bright LED at
around 1mA-2mA it might be ok with something like a 220uF capacitor,
depending on what he means by 'soft'.

At higher currents, it's cheaper and better to just put an emitter-
follower in there (series resistor) and an R-C to the base. I don't
see why a little BJT would be objectionable.

But software would be even better.

Best regards,

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TakeThisOuTspeffEraseMEspamspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
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2001\06\06@012430 by Tony Nixon

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John Pearson wrote:
>
> Dang, I knew I left out a very important parameter: My pic clock speed is
> 240Hz. I don't think this has a software solution.

What about something like this...

Sub_On  movlw 10h
Loop    Led_On
       call _On
       Led_Off
       call _Off
       addlw 0xFF
       btfss STATUS,C
       return
       goto Loop

_On     addwf PCL
       nop
       clrw
       nop
       nop
       nop
       nop
       nop
       nop
       nop
       nop
       nop
       nop
       nop
       nop
       nop
       nop
       return
_Off    subwf PCL
       return

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Tony

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2001\06\06@050416 by Roman Black

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John Pearson wrote:
>
> How can I soften the blinking of an LED so that it doesn't go on and off so abruptly? Is there a way of doing this with just an RC and no transistor?
>
> I am blinking an LED with a pic port and I can use either high or low to light LED.


Hi John, just try putting a big cap like 330uf
to 1000uF range across the led. With most normal
series resistors and flash speeds this will work
fine. Using PWM is a bit of overkill and you
won't gain any efficiency anyway. (if it's battery
operated).

Another option is to use a smaller cap and maybe
2 PIC pins, one is the ramp up/down pin with a
larger resistor (slower ramp) and the other pin
has a small resistor for full brightness in the
middle. Just an idea.
:o)
-Roman

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2001\06\06@160327 by Harold M Hallikainen

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On Tue, 5 Jun 2001 22:55:31 -0400 Spehro Pefhany <EraseMEspeffspamINTERLOG.COM>
writes:
{Quote hidden}

       A cheap FET would be better in that you could use a larger resistor and
smaller capacitor. I'd use an N channel FET, source to ground, drain to
LED with current limit resistor. PIC drives base thru resistor. If the
resistor is big enough, you may be able to rely on miller effect
capacitor multiplication of the gate-drain capacity. If not, a capacitor
between the gate and drain will have it's value multiplied by the gain of
the circuit over what you'd get with the capacitor going to ground, again
allowing an even smaller capacitor.
       However, as below, software is better, but here's a hardware solution
with small parts.

Harold

>
> But software would be even better.
>
> Best regards,
>
>
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> Spehro Pefhany --"it's the network..."            "The Journey is
> the reward"
> RemoveMEspeffEraseMEspamEraseMEinterlog.com             Info for manufacturers:
> http://www.trexon.com
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> http://www.speff.com
> Contributions invited->The AVR-gcc FAQ is at:
> http://www.bluecollarlinux.com
>
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2001\06\08@122926 by Ken Walker

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RC..cap to ground...R to pic pin....led across C...R is the current limiting
resistor for the led and is also used in the RC timing calculation '1' turns
it on '0' turns it off...or C to Vcc where '1' turns it off and '0' turns it
on. Just play with values of C and the off/on/off of the pic to get what
your happy with. Or you could pwm your pic pin.

Mr Smiley

{Original Message removed}

2001\06\12@114552 by Andre Abelian

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use PWM instead of turning on and off just change the duty cycle.

Andre


How can I soften the blinking of an LED so that it doesn't go on and off so
abruptly? Is there a way of doing this with just an RC and no transistor?

I am blinking an LED with a pic port and I can use either high or low to
light LED.

Thanks

John

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2001\06\12@155817 by Dal Wheeler

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I did something like this for a magic trick I helped a local guy with a
dinner theater develop.  The LED's were controlled by two nested loops.  The
inner loop controlled the duty cycle and the outerloop controlled the duty %
rate via a lookup table (the LED's I used had a percieved brightness rate
that wasen't exaclty linear; more logrithmic, so I plotted a curve in a
lookup table).  --A third loop could get the thing to blink; in my
application it was sufficient to bloom on and fade off.  Sorry, I don't have
the code handy, it was a few years ago, but you should be able to hack
something pretty quick.

-Dal
{Original Message removed}

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