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Old 29th September 2005, 01:43 AM   #1
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Default Peak-hold VU meter

I want to find a schematic for a simple VU meter with peak hold. (like those old cassette decks with an FL display that would hold peaks for a sec or two).

Im googling, but turned up nothing. Anyone help me?
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Old 29th September 2005, 05:28 PM   #2
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oops, i think I posted in the wrong forum, so mods delete this, as I am going to double-post in the right forums. thx.
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Old 30th September 2005, 03:24 PM   #3
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Anyone??
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Old 30th September 2005, 05:15 PM   #4
Cobra2 is offline Cobra2  Norway
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Default Eq

Maybe look for an old equalizer or tape-deck schematic, or salvage the parts from such a unit?

Arne K
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Old 30th September 2005, 05:19 PM   #5
Nasse is offline Nasse  Finland
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How about a peak led that stays lighted for some time, as addon with analog meter
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Old 30th September 2005, 07:10 PM   #6
macboy is offline macboy  Canada
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Take a look at the National LM3915. In the datasheet you will find schematics for a full-wave-rectified peak-hold circuit. With this type of circuit feeding the 3915, you will have a 10-LED bargraph with fast 'attack' and slow 'decay' (rises quickly but falls slowly).
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Old 30th September 2005, 07:13 PM   #7
moamps is offline moamps  Croatia
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Here is an idea:

1. Use the LM3916 as a log display.
2. Make two active rectifiers: VU and peak.
3. Make a CMOS oscillator at ca 50-150Hz.
4. Use a CMOS audio switch-selector (4016,66,4051,52,53) and synchronously switch (using the oscillator) dot/bar mode and source signal (peak/VU) on the LM3916 .

This method should allow you to get VU reading in the bar mode and peak reading in the dot mode.

Regards,
Milan
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Old 30th September 2005, 10:36 PM   #8
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yea, thats kind of what I mean. The old 80s technics decks had the FL display that would hold that one anode where the peak was for about one second or two.
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Old 3rd October 2005, 12:26 PM   #9
macboy is offline macboy  Canada
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Quote:
Originally posted by moamps
Here is an idea:

1. Use the LM3916 as a log display.
2. Make two active rectifiers: VU and peak.
3. Make a CMOS oscillator at ca 50-150Hz.
4. Use a CMOS audio switch-selector (4016,66,4051,52,53) and synchronously switch (using the oscillator) dot/bar mode and source signal (peak/VU) on the LM3916 .

This method should allow you to get VU reading in the bar mode and peak reading in the dot mode.

I also had the idea of using both a bar mode display and a separate dot-mode one to display the peaks. Your method would work but I think that it is needlessly complicated. Since the LM3915/6 has open-collector outputs, you can simply connect two chips to the same LEDs. That way either or both can draw current throught each LED, superimposing the bar display (for instantaneous level) with the dot display (for peak level).
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Old 3rd October 2005, 05:04 PM   #10
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I got it to work using his method.

used a bilateral switch, an op-amp oscillator, and two op amp active rectifiers with different RC time constants.

It works, but the only thing I dont like about it, it wont hold the peaks for a nano second, and it will slowly fall.

If i use a bigger cap, it will hold the peaks, but take way to long to fall.



I want it to hold the peaks for 1 second, and fall very rapidly. Not hold the peaks for a nano second, and fall like turtles.


hmmm.
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