mik

LM39XX family
« on: August 08, 2006, 08:53:19 AM »
Gentelmen, does it possible to get a 20 segments led meter ( 1 liting led for 1 db ) cascoding 2 of these IC ?

M.


olafmatt

LM39XX family
« Reply #1 on: August 08, 2006, 09:39:14 AM »
At least the version I know about don't allow for this (at least not directly). There are:

LM3914   linear version
LM3915   logarithmic 3 dB/step version
LM3916   Audio VU version

Cascading 2 LM3915 together gives 20 segement display over a 60dB range due to the 3db step between LEDs. I have done this before and use it regularly, see: http://www.akustische-kunst.org/audio/peakmeter.html
For better reslution around the 0dB are the 3916 has smaller dB steps between LEDs there.

In order to build something with 1dB per LED you could probably use the linear version (LM3914) and build your own liner->log converter. But getting this accurate is probably quite complicated. Could be easier to immitate the LM3915's internel circuit using descrete parts, changing some resistors to give 1dB steps.

Olaf

mik

LM39XX family
« Reply #2 on: August 08, 2006, 10:06:09 AM »
thank you very usefull info.
 :thumb:

M.

mik

LM39XX family
« Reply #3 on: August 08, 2006, 11:38:00 AM »
I do appreciate it very mutch, thank you
Rogerfoote

M.

StephenGiles

LM39XX family
« Reply #4 on: August 09, 2006, 02:53:02 AM »
Roger - you should always take a break!
The best place to find a helping hand is at the end of your arm!

mik

LM39XX family
« Reply #5 on: August 09, 2006, 05:50:24 AM »
thank you for this great info,
My goal is to obtain a "linear" going in the first 10 db of the scale. On page 21 of the data for LM3916 is show a schematic of a 17 segment ( quite good to me ) obtained cascoding 2 LM3916. but the first 5 step has a log increment, then the scale go linear with one db for led ,  I need the contrary of that configuration,

it seems to me is just an "how to" configuration issue.

M.

mik

LM39XX family
« Reply #6 on: August 10, 2006, 10:49:08 AM »
thanks Roger
M.


 

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