rack mount meterbridge for my board, my first project

[les666paul]

hey guys,

ive got a mackie 1604 vlz pro board rackmounted, and im wondering how, and what i would need to make a rack mounted meterbridge (hardly a bridge at all, more like a meter-rack ) to go next to it, it would be 2 rack spaces, and 16 channels.

thanks
james

and maybe some VU meters too

 

[Brian Roth]

Even assuming two rows of 8 meters, those will be some pretty small VUs!

Bri

 

[les666paul]

can any one recomend any parts i will need or kits i can use to make the meters

i dont NEED VU meters :green:

 

[Guest]

Theres a couple of threads in the lab at the moment

http://www.groupdiy.com/index.php?topic=12910

http://www.groupdiy.com/index.php?topic=12888

 

[shaddai]

Thought about the same for my 1640...because 4 little lights (-20,0,+10 and clip) isn't saying a whole lot. Haven't fiddled with it, but this is how it'd work in my feeble newbie mind:

My idea was built a 10 segment led bar graph meter (look at a Mackie HDR/MDR)driven by an LM3915 type IC per channel. Signal would be metered from the 1640's send side of the insert jack, and would then be wired so an actual useable insert jack would be on the back of the meter box. This would give you a 10 seg led metering channel signal post gain & low cut, but pre/post-insert (depending on how you set it up) & pre-eq. Use 2 lm3915's per channel and another 10 seg bar graph, and you even set it up for a 20 seg display. Could probably cram it in a little 1u box too. Add 6 more channels for the subs & mains...and voila, meters everywhere.

Anyway, most of the details should be able to be worked out from the data sheet & commonly available information. I'm pretty sure if the 3915 is too expensive, there are other comparable IC's...and that's as far as I got with it


Todd

 

[les666paul]

so i could get 16 of these

http://www.ledtronics.com/ds/CBG1500/(LBG1500B-1R5Y9G
9 green, 5 yel., 1 red)

what would i use to drive it

i want 15 led's if possible :green:
???......... :green:

 

[JLM Audio]

We have been working on this little beast above for a while for some of our new gear as a general stereo VU, PPM, Gain reduction Meter.

2 x 30 ledmeter with peak hold & decay. It uses one PIC IC with 4 x 10bit A/D inputs and 4 normal cmos IC's which all fit on the back of the LED PCB.

 

[les666paul]

gow much does that cost

i need 16!

LM3915N-1

is this what i would use to drive a ten light bar graph

is this the same thing
LM3915N-1 on eBay

 

[shaddai]

Yup, you've got the idea, and that is the LM3915 IC you have there. I haven't done any digging to see if there's a chip that would drive 15 segments though. I know with 2 3915's you can drive 20 segments though..maybe someone else will pop up & know something.

JLM Audio's has a REALLY interesting feature though:

2 x 30 ledmeter with peak hold & decay

That peak hold & decay could be awfully useful if you're using a digital recorder behind your 1604. You'd just have it set up so if it holds red, you have a digital over to go back & redraw. Set it up so that it holds the peak long enough to scribble the time & track number down.

Anyway, you now know as much as I do about it.

Todd

 

[PRR]

> if the 3915 is too expensive

Should be $3. Even Radio Shed was selling it around that price.

Heck. Go to www.digikey.com, put "LM391" in the Search box. They have ample stock of 3914, 3915, and 3916 in DIP-18 package all for under $3 each.

> That peak hold & decay could be awfully useful

You can do that with LM3915. The 3915 does not do it by magic, it actually just displays the voltage you give it. Peak hold/decay is in your rectifier, and if you'd go to the National.com you find such schemes in the datasheets and the application notes. They don't show a combination semi-VU-bar and peak-dot display, but that can be done with two detectors and an oscillator to rapidly switch between the two modes. (At some point, it does get so insane that Joe's PIC plan looks attractive. You trade hardware complexity for software complexity, but you have to build hardware whereas software can be told to copy itself.)

Stacking two of the dB-VU chips is also in the notes, and at $3/each you can't whine too bad about "needing 1.5 chips". Just ignore the extra pins.

> Even assuming two rows of 8 meters, those will be some pretty small VUs!

There are edgewise meters that can be stacked that dense. I would not want to have to read them.

If he's going LED, there is a standard 8X8-array LED that would give 16 channels of 15 steps in 2 inches square. The 8X8 module goes for around 4/$10 if you find it surplus. Not sure I'd want to work on that either.

 

[shaddai]

> Even assuming two rows of 8 meters, those will be some pretty small VUs!

There are edgewise meters that can be stacked that dense. I would not want to have to read them

As far as real needle swingin meters, I agree with PRR..I wouldn't want to work with 16-22 of them crammed in a little panel..and besides, these are Mackie 1604's and 1640's we're talking about.

I own a Mackie MDR, and it's got 24 channels of LED metering (packed into about 12-14" horizontal and about 2u vertical) and it's very easy to see & understand what's happening in a split second. It's nice & bright and spaced out enough to easily distinguish what channel is what.Have a look-BIG mdr pic


Todd

 

[EZ81]

Joe:

We have been working on this little beast above for a while for some of our new gear as a general stereo VU, PPM, Gain reduction Meter.

If this is not a trade secret: Do you do the meter ballistics etc. in software? (If yes: do you have any hints to get me started?) Or are there opamp rectifiers with the necessary time constants a la LM3915 datasheet involved?

TIA,
;Matthias
(currently fighting a noisy power supply for a diy plasma display... :evil: :evil: )

 

[JLM Audio]

If this is not a trade secret: Do you do the meter ballistics etc. in software? (If yes: do you have any hints to get me started?)

We are still working on the full VU & PPM timing spec internally. But basically we have tried both opamp based rectifier and timing and internal versions. With internal the first 2 A/D inputs are biased to half its input max volts and takes the AC waves form. In software this is rectified. The rectified number is then compared to a table which has the step levels stored in it. At present the first 11 red leds are 2dB steps and all other leds are 1dB steps. The peak is held for a preset time before it fades stepping back a led at a time. Implementing the VU or PPM is a matter of applying filtering and attack & release to the A/D rectified samples. Which is easier said then done.

We also have working a 2 x 40 LCD type display as it can display lots of other info as well.

Top line shows the VU/Peak Meter and bottom the 10dB compression meter

 

[EZ81]

Thanks Joe,

Which is easier said then done.

:grin: :grin:
Unless i'll be putting the thing into mass production, i'll keep the hardware rectifier/timing circuit then...

the LCD looks like a great idea :thumb:

;Matthias
(got the power supply working :sam: :sam: )

 

[chriss]

Joe,

would you mind sharing a few more details on that meter? i'm very interested...

chris

 

[gyraf]

There was an "Elektor" diy-lcd-vu-meter some 10years ago, looking a bit like that..

 

[chriss]

was that really using a microcontroller?

 

[cuelist]

Slightly (!) OT but I'm working on a much bigger one... :green:

Each one has 112 individually controlled full colour (RGB) LEDs, driven by custom ASIC's.

 

[chriss]

Oh my God! That must be for quite a huge mixer's meterbridge.

 

[clintrubber]

Cuelist, that's an awesome bar ! :shock:
Would it be for measuring the output from this amp perhaps ?

But serious, when looking for cheap parts for a lot of LED bars, see if you can find a Beh. MB8000 and use it as is or 'reshape' it.
I bought mine for my MX dirt cheap, they were dumping these a few years ago.

I paid around EU90 then, and saw one now for EU114.