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'[PIC]: Measuring amplitude?'
2001\07\06@164034 by Linux HA

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I would like to measure the amplitude of a signal (actually only the top
half :-). Does anyone have any suggestions or pointers, I'll be using
the 16F877 ICD as the proto and hope to move over to the 12C67x later.
The frequency is only 120KHz.

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2001\07\06@165249 by Barry Gershenfeld

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>I would like to measure the amplitude of a signal (actually only the top
>half :-). Does anyone have any suggestions or pointers, I'll be using
>the 16F877 ICD as the proto and hope to move over to the 12C67x later.
>The frequency is only 120KHz.

Well then, anytime the processor isn't busy just grab signal
samples off the A/D converter.  Record the highest reading you
get after grabbing some number of samples...that's the + amplitude,
assuming it was a real signal you were reading.

Barry

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2001\07\06@170118 by Linux HA

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Barry Gershenfeld wrote:

>>I would like to measure the amplitude of a signal (actually only the top
>>half :-). Does anyone have any suggestions or pointers, I'll be using
>>the 16F877 ICD as the proto and hope to move over to the 12C67x later.
>>The frequency is only 120KHz.
>>
>
> Well then, anytime the processor isn't busy just grab signal
> samples off the A/D converter.  Record the highest reading you
> get after grabbing some number of samples...that's the + amplitude,
> assuming it was a real signal you were reading.

Sometime things are just that simple, thanks!

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2001\07\06@172851 by Kevin Olalde

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So Neil, what type of X10 thing are you building?  Maybe a DIY ESM type
thing?

Kevin

Linux HA wrote:
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2001\07\06@210732 by Olin Lathrop

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> > Well then, anytime the processor isn't busy just grab signal
> > samples off the A/D converter.  Record the highest reading you
> > get after grabbing some number of samples...that's the + amplitude,
> > assuming it was a real signal you were reading.
>
> Sometime things are just that simple, thanks!

Sometimes, but not this time.  You said the frequency was 120KHz.  That's a
lot faster than the PIC A/D can sample.  You would have to sample every 4uS
to beat the Nyquist rate.  You could do some fancy pseudo random sampling,
but I think a little external hardware is called for here.  Fortunately this
is pretty simple.  All you need is an op amp, diode, capacitor, and
resistor.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, .....olinKILLspamspam.....embedinc.com, http://www.embedinc.com

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2001\07\07@012132 by Linux HA

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Kevin Olalde wrote:

> So Neil, what type of X10 thing are you building?  Maybe a DIY ESM type
> thing?
>


Awwe, what gave way the secret? ;-) Was it Dave's post on CHA?

Actually it's more of a X10 sniffer thingy with amplitude measurement.
A 1 1/2 bit has a value of 0x01 to 0xFF and a 0 1/2 bit has a 0x00 sent.
A simple solution. The program back on the PC interprets the value. I
still have a lot to do hardware-wise and software-wise but it's doable.
Now onto looking into the peak detector ...

BTW, this may take me a few months to build (spare time and all ...).

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2001\07\07@020114 by Kevin Olalde

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Linux HA wrote:
>
> Kevin Olalde wrote:
>
> > So Neil, what type of X10 thing are you building?  Maybe a DIY ESM type
> > thing?
> >
>
> Awwe, what gave way the secret? ;-) Was it Dave's post on CHA?

No, just guessing. I haven't been following CHA since I subscribed to the
PICLIST.

> BTW, this may take me a few months to build (spare time and all ...).

I know the feeling.  Have fun, post here when you've got something to try
(assuming it'll be an open project).

Thanks,
Kevin

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