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Old 21st December 2006, 06:05 PM   #1
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Default LED VU meter

LED VU meter for ZV9
I would like to build an LED VU meter to measure the DC offset for each channel.
I imagine there to be 5 or 6 LEDS where 1 would glow for lowest output whilst 5 would glow at max.
I just finsihed populating my ZV9 boards and thought this might be an interesting way to use the iconic Pass Blue LED.
Please help and newbie figure this out.
Thanks for your time
Neil
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Old 22nd December 2006, 05:06 AM   #2
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all you need is the LM3915 dot/bar driver from national. very easy to use!
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Old 22nd December 2006, 04:06 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
a novel use for a bargraph.
Now which should you choose? lin, log or VU?

DC output offset monitoring with a couple of reds, a couple of orange and the other 5 for green to confirm that all is OK, probably best in dot mode.
The top limit could even overflow to turn off the output relay.
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Old 25th December 2006, 09:07 PM   #4
cpemma is offline cpemma  United Kingdom
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The basic LM391x has a range of 1.25V, you can extend that down a bit but for usual offset voltage magnitudes you'll need a voltage amplifier stage. Measuring both positive and negative offset levels also adds to the complexity, but an opamp amplifier with virtual earth set to mid-range on the bargraph may solve that.

However,
Quote:
I would like to build an LED VU meter to measure the DC offset for each channel...I imagine there to be 5 or 6 LEDS where 1 would glow for lowest output whilst 5 would glow at max.
Do you mean "DC offset" in the conventional sense of setting up an amplifier, or do you want an indication of the magnitude of the speaker voltage when music's coming out? That's a different kettle of fish, much easier. See LM3915/LM3916 datasheets.
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Old 26th December 2006, 02:30 AM   #5
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Thanks for the response. I guess i meant magnitude of speaker voltage
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Old 26th December 2006, 05:02 AM   #6
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Quote:
Originally posted by neil_kaye
Thanks for the response. I guess i meant magnitude of speaker voltage
Awww, I think you actually sparked some interest in the fact people thought you wanted to measure and display the DC offset voltage and not just the output level.
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Old 26th December 2006, 08:53 AM   #7
AndrewT is offline AndrewT  Scotland
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Yes,
green, orange, red, shut down (with latch) on DC output offset was a much more interesting project!
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Old 26th December 2006, 03:29 PM   #8
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ughhh, i am just a beginner... making htis up as i go along.
A year ago i didn't know how to hold a soldering iron.
Turns out with a little help of google there a about 100 simple circuits doing exactly what i want.
Perhaps for the next project i might attemopt DC offset... first go to figure out what it is though
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Old 27th December 2006, 07:43 AM   #9
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I got some boards made for a VU meter a little while ago.

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