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'Filtering PIC Power maybe?'
1999\03\09@012716 by Troy P.

picon face
Hi all,
   I have a PIC controlled CDI ignition circuit that I have been
building on for a while and I have got it down to all the voltages are
right but now when the PIC fires the SCR to discharge the CAP into the
coil the PIC seems to stop operating.

At first I believe the problem was that the I/O pins were being
rewritten so I re-initialized the I/O pins at different points in the
code and this allowed the PIC to operate longer but then it quit again
and I noticed that it had become very hot to the touch.

Does anyone have any ideas? Maybe some way to isolate the PIC from the
rest of the power. I am almost out of ideas. Anything will help.
Thanks
spam_OUTTroyTakeThisOuTspamignition.hell

1999\03\09@013747 by Tjaart van der Walt

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face
"Troy P." wrote:
>
> Hi all,
>     I have a PIC controlled CDI ignition circuit that I have been
> building on for a while and I have got it down to all the voltages are
> right but now when the PIC fires the SCR to discharge the CAP into the
> coil the PIC seems to stop operating.
>
> At first I believe the problem was that the I/O pins were being
> rewritten so I re-initialized the I/O pins at different points in the
> code and this allowed the PIC to operate longer but then it quit again
> and I noticed that it had become very hot to the touch.

'Hot to the touch' sounds as if you are getting spikes on your
outputs that are running back into the PIC and shorting via
the protection diodes.

I have found nothing to be as fast as a tranzorb for absorbing
nasty spikes. Hook a 0.6Ke 5V tranzorb over the output pins.

--
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1999\03\09@024050 by Gerhard Fiedler

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At 08:46 03/09/99 +0200, Tjaart van der Walt wrote:
>I have found nothing to be as fast as a tranzorb for absorbing
>nasty spikes. Hook a 0.6Ke 5V tranzorb over the output pins.

they like some series impedance (in the path which you want to protect) to
take the energy, depending on the application.

ge

1999\03\09@173710 by Tony Nixon

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picon face
Troy P. wrote:
> and I noticed that it had become very hot to the touch.

The 'spikes' may be causing the PIC to 'latch up' causing internal
shorts.

> Does anyone have any ideas? Maybe some way to isolate the PIC from the
> rest of the power.

My programmable ignition kit is now in over 2000 cars and have been in
operation for over two years.

I have a 100R resistor in series with each input to the pic that is
controlling any engine components, ie points, coil drivers etc. After
this resistor, on the PIC side, are a diode to 5V and one to GND. I used
IN5819's, but I have heard that ordinary IN4002's work OK. There is also
a 10n cap from the diode junctions to GND.

You may need to isolate the SCR from the PIC.

--
Best regards

Tony

PicNPoke - Multimedia 16F84 Beginners PIC Tools.

http://www.picnpoke.com
Email .....picnpokeKILLspamspam.....cdi.com.au

1999\03\10@113420 by Reginald Neale

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face
At 12:21 AM 3/9/99 -0600, you wrote:
>Hi all,
>    I have a PIC controlled CDI ignition circuit that I have been
>building on for a while and I have got it down to all the voltages are
>right but now when the PIC fires the SCR to discharge the CAP into the
>coil the PIC seems to stop operating.
>
>At first I believe the problem was that the I/O pins were being
>rewritten so I re-initialized the I/O pins at different points in the
>code and this allowed the PIC to operate longer but then it quit again
>and I noticed that it had become very hot to the touch.
>
>Does anyone have any ideas? Maybe some way to isolate the PIC from the
>rest of the power. I am almost out of ideas. Anything will help.

Troy:

Could be internal latchup in the PIC. The automotive environment is
really NASTY, and CDI circuits generate huge transients on purpose!
You're probably going to need some massive decoupling between the
PIC and everything else. For starters, try powering the PIC temporarily
with a separate supply, like 4 NiCds or 3 D cells, well bypassed with
caps; and use maximum possible series resistance with I/O lines.
See if that makes a difference.

Reg Neale

1999\03\12@172726 by Richard A. Smith

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face
On Wed, 10 Mar 1999 09:34:45 +1100, Tony Nixon wrote:

>
>You may need to isolate the SCR from the PIC.
>

I just finished the first prototype of a unit that controls
a Cheston heater.  It's phase controled via 2 inverse
parallel SCR's which at peak run 350 amps at 480 VAC.  To
achive the proper isolation beetween the SCR's and the CPU
I had to use a gate trigger transformer.  The CPU sits on
the primary side and the SCR is on the secondary side
connected to the anode and the gate.  To fire the scr you
pulse the xformer.  This sends several large spikes into
the gate and turns on the SCR.  Be warned all gate xformers
are not created equal and you need to do a little research
to get right one for your SCR.  (Or at least in my case
they were)



--
Richard A. Smith                         Bitworks, Inc.
EraseMErsmithspam_OUTspamTakeThisOuTbitworks.com               501.521.3908
Sr. Design Engineer        http://www.bitworks.com

1999\03\12@200235 by Harold Hallikainen

picon face
On Fri, 12 Mar 1999 16:26:58 -0600 "Richard A. Smith"
<rsmithspamspam_OUTbitworks.com> writes:
>On Wed, 10 Mar 1999 09:34:45 +1100, Tony Nixon wrote:
>
>>
>>You may need to isolate the SCR from the PIC.
>>
>
>I just finished the first prototype of a unit that controls
>a Cheston heater.  It's phase controled via 2 inverse
>parallel SCR's which at peak run 350 amps at 480 VAC.  To
>achive the proper isolation beetween the SCR's and the CPU
>I had to use a gate trigger transformer.  The CPU sits on
>the primary side and the SCR is on the secondary side
>connected to the anode and the gate.  To fire the scr you
>pulse the xformer.  This sends several large spikes into
>the gate and turns on the SCR.  Be warned all gate xformers
>are not created equal and you need to do a little research
>to get right one for your SCR.  (Or at least in my case
>they were)
>

       Might also try the MOC3010, MOC3020 series, etc.  These are
optically isolated triac drivers.

Harold


Harold Hallikainen
@spam@haroldKILLspamspamhallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

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1999\03\15@100419 by Richard A. Smith

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face
On Fri, 12 Mar 1999 19:58:31 EST, Harold Hallikainen wrote:

>>the gate and turns on the SCR.  Be warned all gate xformers
>>are not created equal and you need to do a little research
>>to get right one for your SCR.  (Or at least in my case
>>they were)
>>
>
>        Might also try the MOC3010, MOC3020 series, etc.  These are
>optically isolated triac drivers.

Oh yeah I forgot those... for non phase control stufff
these will probally work great.  I had  trouble useing them
because I had to use the line voltage (480) to trigger the
SCR's.  To keep the gate from being destroyed at the peak
of the cycle I had to have a large resistor in series with
the gate.  But the voltage drop across the resistor kept me
from being able to trigger at < 30 or > 300 degrees. Which
in my application was important so I had to switch to
xformers.

IMHO the MOC's will be an eaiser (less complicated hadware
and software) soulution.


--
Richard A. Smith                         Bitworks, Inc.
KILLspamrsmithKILLspamspambitworks.com               501.521.3908
Sr. Design Engineer        http://www.bitworks.com

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