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Old 4th January 2013, 06:47 PM   #1451
davada is offline davada  Canada
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Quote:
Originally Posted by dimitri View Post
Why not two of them in control loop: (A*sin(wt))^2+(A*cos(wt))^2)=A^2, no ripple (in theory)
Hi Dimitry,

I've been giving this some thought.
If the summed levels are out by 1% this causes roughly 165mV ripple.
If we use one output signal as a reference and use an AGC on the other output signal,
we might be able to make this work. But it will come with extra complexity.

If we do this with a Gilbert multiplier core, we have access to every part of the multiplier.
Once we get it right then look at some of the 'simpler to use' multiplier ic's.

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Old 4th January 2013, 08:47 PM   #1452
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Quote:
Originally Posted by davada View Post
This is the circuit used and spectrum of the output.

For 6Vrms input to the lamp there is a 5.56Vdc output.
At 3Vrms the output drops to 0.823Vdc.

That's not very linear.

I'm concerned about the level of distortion as well.
This is with a 0.1uF feedback cap on the output amplifier.
I's much worse with out the cap.
R is 10M.
An ignorant question
dont you need at least 3 points to determine if it is linear or nonlinear?
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Old 5th January 2013, 12:31 AM   #1453
davada is offline davada  Canada
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Originally Posted by myhrrhleine View Post
An ignorant question
dont you need at least 3 points to determine if it is linear or nonlinear?
Lol.

Yes. I suppose a few more point would be better.

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Old 5th January 2013, 01:43 AM   #1454
1audio is offline 1audio  United States
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Don't forget zero is part of this curve. More points help.
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Old 5th January 2013, 05:42 AM   #1455
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
Don't forget zero is part of this curve. More points help.
Okay I'll do a little chart tomorrow.
But the distortion and feed through is too high and I've lost interest.

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Last edited by davada; 5th January 2013 at 05:53 AM.
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Old 5th January 2013, 05:30 PM   #1456
RNMarsh is offline RNMarsh  United States
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My take is this --- if you cut the input from 5.56v by exactly 1/2, the output should do same (2.78). It was way off at .823v and thus not deemed a worthy candidate. Have I got that right? -RNM

Last edited by RNMarsh; 5th January 2013 at 05:33 PM.
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Old 5th January 2013, 05:44 PM   #1457
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
My take is this --- if you cut the input from 5.56v by exactly 1/2, the output should do same (2.78). It was way off at .823v and thus not deemed a worthy candidate. Have I got that right? -RNM
That's about it.

Now this could just be scaling and not necessarily non linear.
But I was here watching the points as they went by.
It was a poor communication on my part just to say it's non linear and I think this is
what was being said.
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Old 5th January 2013, 06:02 PM   #1458
davada is offline davada  Canada
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If I could point a laser at the filament of the lamp and heat it this way I could control the resistance of the lamp by the Intensity of the laser.

It would have to be one big laser though.
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Old 5th January 2013, 07:13 PM   #1459
davada is offline davada  Canada
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There is one approach to peak detection that I haven't ventured into and that is FFT.

Here is a complete project I found on the web which can be scaled down and modified for this purpose.

This is really quite cool. Coded for a PIC. I'm using the smaller pin version of this PIC to control the oscillator but I can upgrade to the larger pin count PIC. It looks like I need more pins anyway.

Since the peak value is not required to stabilize the loop, the lamps do this, this may be workable. The sample speed has to increase to cover a greater band width or we can just let it wrap around since it's a single frequency we know what that is.
We don't need the LCD driver code so that's a big saving there.


Check this out.

Real-Time Audio Spectrum Analyser - WFFwiki

Cheers,
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Last edited by davada; 5th January 2013 at 07:28 PM.
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Old 5th January 2013, 08:01 PM   #1460
RNMarsh is offline RNMarsh  United States
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It doesnt look too unwieldly and a pcb is already made to try it with. Now... what is the goal, again? The cause of thd that this is going to affect a reduction? Just checking... sort of a resync operation. -RNM
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