Adding Volume LCD display ...

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Hi everybody,
i'm just about to build amplifier based on the LM3886.
It should be a 5.1 type .
I would like to add to the basic amplier a general volume command and (this is where the thing come difficult) i would like to add a lcd which display the sound level (in Db for exemple).
I can think that it will require analogic to numeric conversion and binary to decimal conversion but i can't go further ...

Do you know where i can find help please ?

Thank you very much
Are you referring to a volume (sound pressure level) display or a output voltage (level) display?

If you want a SPL meter, you could hide an electret element somewhere in the room (perhaps even in the amplifier case) and calibrate it's output voltage with a good SPL meter. The output voltage can be fed into a A/D converter and treated accordingly.

You could also amplify the signal appropriately (from the electret element) and feed it into a LM3915 (log LED display driver).

If you just want a level output, the LM3915 is the easiest way to go.
I'm actually doing/have done something similar. I have an amp that's got a bitmap LCD and is all digitally controlled. When you adjust the volume, a little bar increases/decreases and tells you dB level. Given that I had an LCD, I already had a microcontroller (8051 in my case)...The LCD connected via SPI to the micro. The audio did indeed come to the micro via A/D converter. Then you just have to write a basic algorithm to convert that binary number to dB. Pretty easy to do if you know a micro decently well. Anyway, that would be my solution, just use a microcontroller to do it.

i have well understand your answer...
I agree that a micro controler can do the job but my big problem is that i don't master at all this kind of technology...
i can imagine how thing should be employ but i can't built the circuit..

do you know where i could find a kind of frame or examples in order to start in project ?

Thank you very much
I'd approach it in a slightly different way, but still using a micro - I'd use a digital volume control that can be controlled by the PIC (take a look at PiCAXe) and go from there...

It's easy to find rotary encoders that you can use for other functions too, to control the volume control...

Just a slightly different path - as you then know which volume setting you have (as well as balance etc) stored in the PIC.. much easier to output to a display!

Have fun

National Semi has a chip, the LM3915, which will will read out in 3dB increments, another of their chips will read out in VU. The LM3915 is intended to drive LED Bargraphs -- but you can translate the output (with a little "software in silicon") into numeric values for display on an LCD. without a microcontroller, however, getting the data onto the LCD display is a lot of work. as METAL points out you need to run the data serially -- this necessitates using a microcontroller (from any numer of sources). it is possible but a waste of time to do all the interfacing without a microcontroller.

you can quickly learn to program the Basic Stamp II -- and the company has a bulletin board with hundreds of members to help you out. unfortunately the Stamp doesn't have built in floating point math so you have to do a couple twists and turns to generate logarithms and exponentials. the URL is

the BasicX BX24 from NetMedia costs as much as a stamp but has the floating point math you need -- can be programmed over a serial cable like the stamp -- and has the benefit of 8 10-bit ADC's. The group of users is smaller, the programming language is a little more difficult, but the chip is very useful.

the folks from Netmedia and Parallax also sell LCD's, relay and servo drivers
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