INTOSC / HS - EMI considerations

[arocholl]

For a couple of R/C onboard applications I am using PIC18F family with
overall success, so far working with INTOSC. However, it has a few
clock stability problems, particularly when using RS232 high speed to
download data, it looks very dependent on temperature. This has been
discussed a number of times here.

What I wonder is how dramatic change in EMI could be to move to HS
crystal osc. In my case, I am not concerned on EC/FCC regulations but
on impact on other devices onboard, including but not limited to the
R/C receiver. I got a few suggestions to use INTOSC to limit EMI when
compared to HS (same speed, say 8MHZ) but I was never presented with
real data, so this is more intuition than sciense. To make it worse, I
have no instruments to measure EMI, except try/error and standard
range check. I am looking for more specific data.

Does anyone have info to share, real experiments, or a pointer to
online info on specific EMI curves of HS/HSPLL and INTOSC? Or any
suggestion on how to measure this myself?

TIA

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Ariel Rocholl
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[M. Adam Davis-2]

On 6/17/08, Ariel Rocholl <foros@...> wrote:
> Does anyone have info to share, real experiments, or a pointer to
> online info on specific EMI curves of HS/HSPLL and INTOSC? Or any
> suggestion on how to measure this myself?

A spectrum analyzer is the usual method of checking EMI.

-Adam

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[Ariel Rocholl]

Yes, I wish I would have a SA but not budget for that.

2008/6/18, M. Adam Davis <stienman@...>:

> On 6/17/08, Ariel Rocholl <foros@...> wrote:
> > Does anyone have info to share, real experiments, or a pointer to
> > online info on specific EMI curves of HS/HSPLL and INTOSC? Or any
> > suggestion on how to measure this myself?
>
> A spectrum analyzer is the usual method of checking EMI.
>
> -Adam
>
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> EARTH DAY 2008
> Tuesday April 22
> Save Money * Save Oil * Save Lives * Save the Planet
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[Harold Hallikainen-2]

>> On 6/17/08, Ariel Rocholl <foros@...> wrote:
>> > Does anyone have info to share, real experiments, or a pointer to
>> > online info on specific EMI curves of HS/HSPLL and INTOSC? Or any
>> > suggestion on how to measure this myself?

Have a look at http://www.microchip.com/emc .

Harold


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[Ariel Rocholl]

Yup, saw that but, appart from Microchip saying the EMI of their
INTOSC are much lower than "before", there is no comparison or study
with external OSC.

2008/6/19 Harold Hallikainen <harold@...>:

>>> On 6/17/08, Ariel Rocholl <foros@...> wrote:
>>> > Does anyone have info to share, real experiments, or a pointer to
>>> > online info on specific EMI curves of HS/HSPLL and INTOSC? Or any
>>> > suggestion on how to measure this myself?
>
> Have a look at http://www.microchip.com/emc .
>
> Harold
>
>
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[arocholl]

Yup, saw that but, appart from Microchip saying the EMI of their
INTOSC are much lower than "before", there is no comparison or study
with external OSC.

2008/6/19 Harold Hallikainen <harold@...>:

>>> On 6/17/08, Ariel Rocholl <foros@...> wrote:
>>> > Does anyone have info to share, real experiments, or a pointer to
>>> > online info on specific EMI curves of HS/HSPLL and INTOSC? Or any
>>> > suggestion on how to measure this myself?
>
> Have a look at http://www.microchip.com/emc .
>
> Harold
>
>
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[Bob Axtell-3]

Why not use a ceramic resonator? Ceramic resonators can take much
higher vibration with little loss in operation (unless you are keeping
time).

Yes, the RC oscillators in the PICS have limited utility as a timebase
for RS232 serial. I have rarely been able to make these work, despite
HOURS of trying.

--Bob

On 6/19/08, Ariel Rocholl <foros@...> wrote:

> Yup, saw that but, appart from Microchip saying the EMI of their
> INTOSC are much lower than "before", there is no comparison or study
> with external OSC.
>
> 2008/6/19 Harold Hallikainen <harold@...>:
>>>> On 6/17/08, Ariel Rocholl <foros@...> wrote:
>>>> > Does anyone have info to share, real experiments, or a pointer to
>>>> > online info on specific EMI curves of HS/HSPLL and INTOSC? Or any
>>>> > suggestion on how to measure this myself?
>>
>> Have a look at http://www.microchip.com/emc .
>>
>> Harold
>>
>>
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>>
>
>
>
> --
> Ariel Rocholl
> Madrid, Spain
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