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'[PIC]: LED Blip on Power Up - Follow Up'
2002\01\17@234019 by Sean Alcorn - Avion Sydney

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Hi Guys,

Once again, thank you for all the replies. I decided to put the blip in the
"too hard" basket for the time being and continued on finishing this project
off. I had been testing that the software was correct using my JW parts -
without being too concerned about timing.

I just burnt a plastic part in order to check all my timings and discovered
no blip at all! It's only happening on the JW parts. Not the first time I
have noticed differences between the JW and plastic parts.

Just thought I might share this with the list.

Regards,

Sean

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2002\01\17@235014 by David Duffy

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At 03:34 PM 18/01/2002 +1100, you wrote:
>Hi Guys,
>
>Once again, thank you for all the replies. I decided to put the blip in the
>"too hard" basket for the time being and continued on finishing this project
>off. I had been testing that the software was correct using my JW parts -
>without being too concerned about timing.
>
>I just burnt a plastic part in order to check all my timings and discovered
>no blip at all! It's only happening on the JW parts. Not the first time I
>have noticed differences between the JW and plastic parts.

Try covering the JW's window with black tape. You can get some odd
things happening due to stray light shining on it while operating.
Regards...

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2002\01\18@001444 by David VanHorn

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At 03:34 PM 1/18/02 +1100, Sean Alcorn - Avion Sydney wrote:
>Hi Guys,
>
>Once again, thank you for all the replies. I decided to put the blip in
>the "too hard" basket for the time being and continued on finishing this
>project off.


I think you'll find that the blink is happening in the interval between
power up, and when that port pin gets initted.
You have a lag between powerup, and when the crystal starts singing, and
another between powerup, and when reset de-asserts. That's what you're
seeing. Once the processor is up, it will (depending on your code) get
there quite quickly.

A pulldown resistor will hold that pin low, during the interval before the
processor gets started.

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2002\01\18@013138 by Sean Alcorn - Avion Sydney

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on 18/1/02 3:53 PM, David Duffy at spam_OUTpiclistTakeThisOuTspamAUDIOVISUALDEVICES.COM.AU wrote:

Hi David,

> Try covering the JW's window with black tape. You can get some odd
> things happening due to stray light shining on it while operating.

No. I tried that. In fact I always cover them by habit.

There are definitely some differences.

Regards,

Sean

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2002\01\18@015514 by Jinx

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> A pulldown resistor will hold that pin low, during the interval
> before the processor gets started

I seem to be out-suggested pull-down vs pull-up 3:1, but if the
resistor is a pulldown and the LED is Vcc to pin, surely the
blip will still occur ? It will come on at power-up and go off only
when the pin is driven high

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2002\01\18@032753 by Josh Koffman

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Just as a side note, as I'm sure most people know, black electrical tape
isn't as opaque as it seems. A lot of people seem to like a combination
of tape and aluminium foil.

Josh

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2002\01\18@053923 by Alan B. Pearce

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>Just as a side note, as I'm sure most people know, black electrical tape
>isn't as opaque as it seems. A lot of people seem to like a combination
>of tape and aluminium foil.

Black electrical tape can be quite transparent at Infra Red, which is why it
is not good for using as write protect tabs on 5.25 inch floppies. It is for
this reason that the tabs supplied were always black paper or metallic foil.

My understanding of the process is that the tape is made to appear black by
making its thickness an odd number of half wavelengths thick in the visible
light region, but this then is not an odd number of half wavelengths thick
at the infra red region. It maybe that this applies to the die molecules in
the tape rather than the tape itself.

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2002\01\18@055427 by Vasile Surducan

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On Fri, 18 Jan 2002, Alan B. Pearce wrote:

>
> Black electrical tape can be quite transparent at Infra Red, which is why it
> is not good for using as write protect tabs on 5.25 inch floppies. It is for
> this reason that the tabs supplied were always black paper or metallic foil.
>
 And it's covering a window which is transparent only to visible and UV.
 To be transparent at IR the windows must be made from lithium-clorure,
sodium-clorure and some other hygroscopic salts. A spectrophotometer
analyse actual PIC windows will show the truth.

 I'll search for the nature of this glitch in parasitic capacitive
package which may be different from plastick package ( high capacitive
looses ) and a ceramic one ( better ). Changing the schematic structure to
minimise the glitch effect seems to me the best way.

regards, Vasile

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2002\01\18@105354 by Bob Ammerman

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<snip>

> My understanding of the process is that the tape is made to appear black
by
> making its thickness an odd number of half wavelengths thick in the
visible
> light region, but this then is not an odd number of half wavelengths thick
> at the infra red region. It maybe that this applies to the die molecules
in
> the tape rather than the tape itself.

This doesn't make sense, because you can stretch electrical tape to at least
twice its original length (thus thinning it significantly) without seeing
any strange optical effects.

Besides:

1: It would require high precision control of the thickness

2: What about red, green, blue, yellow, white, etc. electrical tapes?

Bob Ammerman
RAm Systems.

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2002\01\18@221722 by Sean Alcorn - Avion Sydney

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on 18/1/02 4:42 PM, Jinx at .....joecolquittKILLspamspam@spam@CLEAR.NET.NZ wrote:

Hi Joe,

> I seem to be out-suggested pull-down vs pull-up 3:1, but if the
> resistor is a pulldown and the LED is Vcc to pin, surely the
> blip will still occur ? It will come on at power-up and go off only
> when the pin is driven high

I have not tried either, because the blip does not happen on the plastic
parts - only on the JW versions. It must have something to do with the
startup time of the JW parts.

Regards,

Sean

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2002\01\18@231759 by Jinx

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> I have not tried either, because the blip does not happen on
> the plastic parts - only on the JW versions. It must have
> something to do with the startup time of the JW parts

It sounds strange because the 508 has been around for such
a long time the bugs must be well and truly out of it by now. It
may still be a window issue, or even a wonky chip

Of all the micros I've used that have JW parts for development
I don't recall any problems when moving to the OTP. That said,
what you're experiencing makes a good case for flash

uChip have obviously taken a shot at what will likely be most
used in production (C) and what will appeal to the hobbyist (F),
very generally speaking

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2002\01\19@094848 by Roman Black

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Bob Ammerman wrote:
{Quote hidden}

I'm suspicious too. For many years I have always
used black PVC electrical tape on VCRs specifically
as a quick convenient cover for infra-red sensors,
on literally thousands of occasions, and never seen
evidence of IR getting through the tape. This is
standard practice in the VCR reapir industry.
I do buy a decent quality tape though.??
-Roman

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