yet another LED VU meter (3 or 5 LEDs this time)

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mitsos

Well-known member
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May 4, 2007
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OK, I know there are a few other threads on here based on the LM391x, 10 LED chip... Anyway, I'm trying to put together an LED VU for a mic pre project, and since my primary concern ATM is space, I'm leaning toward putting 5 LEDs and a small circuit.  I've been searching for an appropriate IC to do the metering and since I am not familiar with LEDs and their respective ICs, I need help.

I want to do something with 5 LEDs. I've never done much with LEDs but I found a couple of chips, just wondering if there is a favorite like the LM chips are for 10-LED VUs?  The two chips I looked at in my recent web searching are the NTE1561 and Sanyo LB1443N(is this discontinued?). They are SIP 9, and have the same pinout. Anyone have experience with either of these (or another chip maybe)?  Also, the datasheets list the dB values for when each LED lights up (at least that's how I understood it) but they seem to go from -12 to +6... Is there a reason they seem to have the 5th LED at +6dB instead of +3dB? I think this may be adjustable, can't quite see it from the datasheets (sanyo one is more in depth), but maybe someone can shed some light?

datasheets:
http://www.nteinc.com/specs/1500to1599/pdf/nte1561.pdf
http://www.semiconductor-sanyo.com/ds_e/ENN1410B.pdf

Hope this is clear.. and hopefully this will prove useful to others as well. Thanks!
 
The NTE looks pretty simple.
I would guess that you put a red LED on the +6 and (in a +4 environment) call that overload.
Maybe a little TL072 buffer on this and a trimpot to calibrate the levels and you would be in business.
Maybe you don't even need that much.

Sleeper
 
I have used similar chips before in designs to save money, time, and space.  Primary downside is you are stuck with their choices, and these chips seem to come and go, so when they become obsolete it is a PIA for large scale production.

For your purposes I don't care for the choices. I'd rather see something like peak response in 6 dB steps below clipping to gauge head room.

You can roll a 4 or 5 LED meter pretty simply with a 339 quad comparator.  You need to be careful about layout and where the switched current goes to prevent corrupting your audio.

If you use that chip I would at least add a clip detector LED closer to the rail than +6dB

Have fun...

JR
 
Sleeper said:
The NTE looks pretty simple.
I would guess that you put a red LED on the +6 and (in a +4 environment) call that overload.
Maybe a little TL072 buffer on this and a trimpot to calibrate the levels and you would be in business.
I'm concerned about that +6 thing... Why do they make VU meters that go to +6?

OK, let's see if I understood even a fraction of what John said.
I don't have the experience many of you have with these things, and I'm trying to do something very simple, with the smallest PCB real estate used.  My main concern is clipping.  I know headroom is related to the PS voltage, but haven't grasped it 100%. For this project, I would be happy with as few as 3 LEDs, or maybe even one that changed colors... But how do I get them to light at certain dB? Is there a simpler method if I used only one LED for instance?

The 339 comparator... never used one, but not sure I want to add another supply rail. These SIP chips work at up to 18V which is what I'll be using in the preamp, one more reason to go with them, I thought.

For your purposes I don't care for the choices. I'd rather see something like peak response in 6 dB steps below clipping to gauge head room.
Yeah, I'm not sure about the numbers either. Hopefully I'll find something more suitable in this or similar package. these were the only chips I found as of now, I'd like to keep it SIP because of space.

If you use that chip I would at least add a clip detector LED closer to the rail than +6dB
Would this be implemented separately from the LEDs driven by the chip?
 
OK... another question... still not sure why they go up to +6dB.. but anyway.. I am looking for chips that do 3 LEDs only, but no luck.
So... Can I use less than 5 LEDs with either of the above chips?  I thought maybe I could leave off the 5th one (6dB) and maybe the first (-12)... Just use one green, one yellow and one red in positions 2, 3, and 4, respectively.

Is this possible, what would I have to do to the other connections?

I want to use this in a 312 circuit with a THAT 1646 output.. Would I be able to take the signal at the 1646 output and send to the VU and to the XLR out? Any possible problems with that?

thanks again!
 
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