High dynamic of the mic / preamp output in a noise level meter

[micpic]

Hello,

I´m designing a noise level meter.
I use an electret mic an preamplifier and a LM3915 to drive 3 LEDs (green, yellow, red, like a traffic light).
For the first time everything is working so-so.

My problem is the high dynamic of the mic / preamp output. The Leds flicker. I want to have solid on or off states of the 3 Leds. It means: The noise is increasing-> green Led turns off and yellow Led turn on. No it is: green Led flickers / turns off for a very short time amd yellow Led turns on / flickers.

What can I do? It hougth about an rectifier or integrator?

regards mic

 

[Verba]

Noise Level Meter

Just put rectifier at the output of your amp and comparators with hysteresis

 

[micpic]

Re: Noise Level Meter

Hello,

I tried rectifier allone but without sucess.
The LM3915 has intern comperators.

You mean instead LM3915 to use several comperators?
Which you can recommend?

 

[Verba]

Noise Level Meter

you are right, there are comparators inside
then just put any large capacitor at the output of rectifier.
can you post your schematic here ?

 

[micpic]

Re: Noise Level Meter

Hello,

here is the schematic:

 

[Verba]

Noise Level Meter

pin 2 of R8 shouldn't be on the ground
you don't have any rectifier. put the simpliest one - series diode, R and C to the ground
sure you don't want any gain on IC1 ? may be you just switched R5, R6

 

[micpic]

Re: Noise Level Meter

Hello, and thanks for helping.

Pin2 of R8 isn´t connected to ground. I only made this misstake in the schematic. In this schem I have no rectifier because it is the design I use as first like described at the first threat.

sure you don't want any gain on IC1 ? may be you just switched R5, R6

I don´t really understand this? Why won´t I have any gain? The gain of ompamp is defined through the proportion of the voltage divider of R5 and R6.

regards Tim

 

[micpic]

Re: Noise Level Meter

Hello,

as you can see in the schematic I used a capacitor an resistor in series parallel to the mic preamp to delay the leds. Now I have to find out the rigth values for cap and resistor so that the leds will be updated in the desired time.

Basicly can I switch a cap an resisitor at the output of the preamp like i have it done?

Now the problem is that the amplification of the preamp is reduced. This is not what I really want...
Some hints on this?


So then