VU meter display circuit wanted

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Othello

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For a VU meter display circuit I am looking for a suitable circuit.
I tried using the high resolution portion of the LM3916 display driver but I cannot get the 'carry' to behave when using several display drivers in succession ( I took several drivers and only used the 1dB steps of each driver for a high resolution display).

Any suggestion for a high resolution display driving 30 to 50 LEDs is appreciated.

Uwe
 
You cannot hear a very small change in level of only 1dB so use two or three LM3915 ICs that have 3dB steps. Its datasheet shows how to cascade them.
 
I am using a few 3916 and yes, the data sheet shows how to cascade them-but it doesn't seem to work exactly that way. Either a LED doesn't light up or it stays on, the cascading is not trivial and if someone has experience with this issue this might help.
All circuits you find on the internet for VU meters circumvent this problem by using only 1one IC thus no need for cascading.

Uwe
 
You could try putting a 10-bit or better ADC behind a rectifier circuit, and feed the ADC result into an MCU. There, you can do anything you want with the LEDs.
 
I have cascaded LM3915 ICs without any problems, using the circuit recommended on the datasheet.
 
I think the 3914/15/16/ are all similar when it comes to cascading.
As I said I use the 3916 because the upper 5 LED drivers offer a resolution of 1 dB and I am tryimg to cascade those portions.
Meaning for 15 or 20 dB display I would cascade 3 or 4 IC's and I use the circuit from page 17 of the application notes, eg. High resolution VU Meter in Dot mode.
And in my implementation the transition between successive ICs is ugly.

Uwe
 
The idea by mneary to use a digital front end is intruiging, but how fast will this be?
I have no experience with this approach and wonder what reaction times to expect, the rectifier front end I am using indicates 10 ms pulses.
In estimating the overal reaction time I would need the ADC reaction time and the time for a controller and associated display circuitry.

Also, does and ADC do the range I am after, from about 1 mV to about 5 volt?

Uwe
 
audio, you can hear 1db amplitude shifts, but only if you're listening for them, and you have to have good ears. 3db's is the point where the brain will go "Hey this is getting louder" without paying attention.
 
Sceadwian said:
audio, you can hear 1db amplitude shifts, but only if you're listening for them, and you have to have good ears.
Click to expand...
I can easily hear a continuous tone being changed only 1dB. But not most music and speech.
 
Because of the Scaling, Its much more practical th Cascade the LM3915 than the 3916.
And these 3Db Steps should be Quite acceptable for any practical application.

However Creating a 30 to 50 LED Display, Requires a VERY WELL DESIGNED PCB.
Or "GROUND LOOPS" Will be a Real Problem, resulting im Many LED's Lighting up due to Oscillations.

When attempting to make this with theses IC's,
"Each IC Requires a: Common Point Ground".

Take care...Gary

 
Gary, I would like to understand your comment better.

Right now I have built a section of the final design using two 3916 ICs displaying a range of 10 dB. My gripe is that the highest LED of the lower display IC sometimes stays lit when it shouldn't and sometimes it does not light up when it should. I have no explanation for this but the little circuit right now is built on a breadboard which might not be optimal for things like ground and contact security.

This is why I find you remarks interesting, I could easily have a ground problem. Where could I learn more about this, the data sheet of the IC doesn't provide much info on this.

Uwe
 
Look at This Circuit and how the PCB is Designed.
It is NOT for the same IC, But the Principle is the same.

** Note how the grounds for each IC are Seperated.
(All parts at each IC Ground near that IC's, Pin2.)
Also, Definately use a 1uF "Tantalum" caps between Pins 2 and 3 of each IC.

You will also need the 20K Resistor, Connected as shown in this schematic. It helps BLANK the #10 LED of the first IC, so it doesn't light when it supposed to be OFF.

**broken link removed**

** Sorry I Don't understand how you think you have a 10dB range.
A Single LM3916 Goes from -20dB to +3dB.

Normally you woul use an LM3915 for the Lower IC and an LM3916 for the Upper IC.
Using these two IC's it will give a range of -40dB to +3dB.

Hope this HELPS.....Gary


 
Here is a Picture of a TRUE "Common Point Ground" on a Circuit Board.

By Using this Grounding Method, you can Totally Avoid
"Ground Loops".

Ground Loops are Small Voltage Drops across varous parts of the Ground Trace. These Voltage Drops can cause oscillations and errors within a circuit.

All parts to the ground here, Come to a Single Point.

Hopefully this helps.....Gary

EDIT: By the way, This type of PCB Design is Extremely Helpful when making boards for IC Power Amps.
 

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Gary thanks, I will study the layout of this PCB.

My range is indeed 10 dB since I use only the 5 upper LEDs of each 3916 for a high resolution display. So using 2 IC's I do get 10 dB in 1 dB steps.

Ultimately I do plan to use something like the 3915 for the lower dB range and to use the high resolution portion of the 3916 for the steps from lets say
-3dB to +12dB, that is the range which is most critical in recording on my tape machine.

Maybe this use of only a portion of each IC aggrevates this problem of faultily lit LEDs...

Uwe
 
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