Re: Sound Level Indicator.

From: Robert Monsen (rcsurname_at_comcast.net)
Date: 01/23/05 

Date: Sat, 22 Jan 2005 17:39:29 -0800

Larry Brasfield wrote:
> <raul@2minclip.biz> wrote in message news:1106407622.309227.213800@c13g2000cwb.googlegroups.com...
>
>>Hi, I teach kids to read and I am always telling them to speak louder.
>>I would like to make some device to measure the sound level. I want to
>>be able to put the device on the desk and if the child is loud enough a
>>green light goes on. Not loud enough, a red light. They are younger
>>kids so I'll use it with a reward system. If they always have a green
>>light they'll get some stickers or something. I would have to be able
>>to change the sensitivity also. Any ideas would be appreciated.
>
>
> Part of the challenge of doing this properly will be to get the
> sensitivity of the indicator to vary with frequency in a way
> that mimics average hearing sensitivity. If you do not do
> this, kids whose voices are near the peak in that sensitivity
> function will have an easier time satisfying your device, while
> those whose voices are off the peak may not realize that
> they need to speak up, having been misled by your device.
>
>
>>Thanks, Raul

Have the level adjusted by a listener with average hearing to just start
to flash when the trainee speaks properly. Much easier than trying to
get it right for everybody.

Here is a circuit that works for me:
(courier, please. Otherwise, it looks like the gibberish it may well be)

                                                     1MEG 10k
                                                     ___ ___
                                                 .--|___|-o--|___|--.
                                                 | | |
      VCC | | |
       | LED 1.5k | /| | Vcc |
      --- 9V ___ | /+|-' | |
       - GND ----|<--|___|---o---< | .-. |
       | \-|--->| | |
      GND \| | | |
                                 10k 1MEG U1D '-' |
                                 ___ ___ | |
VCC .---------o--|___|-o-|___|---. GND |
  | | | | | |
.-. .-. | VCC | | |
| |10k | |330k | + | | |
| | | | | | | | .-------o
'-' '-' | | | | | |
  | | | | | | | U1C |
  | | U1A | | | U1B | | |\ |
  | Cf | |\ | .-. | |\ | '--|-\ |
  | o--|-\ | | |<-)---|-\ | | >-'
  | || | | >---' | | | | >--o--->|-o----o--|+/
  o----||-----o----)--|+/ '-' '---|+/ | | |/
  | || | | |/ | |/ | |
  | | | RSens | | |
  | | | | | |
  | | ' | | |
  | Rf | | | | .-.
  | _ .-. .-. | 1uF --- | | 1MEG
  '-/ \ | | | | |1k | --- | |
   (Mic)| | | | | | | '-'
  .-\_/ | '-' '-' | | |
  | | | | | |
-o-----------o----o--------------o--------------------o----o---- GND
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

U1A is a gain stage. U1B is a comparator, which feeds into a trivial
peak detector (the diode) which decays with a tau of 1s. U1C is a
buffer, so the decay of the peak detector isn't affected by U1D, which
is a comparator that controls how much time the light is on.

The opamps are A-D on a single LM324 chip.

The pot on the V- input to U1B controls level sensitivity.
The pot on the V- input to U1D controls how long the LED stays on after
it's triggered.

The MIC is a cheapo electret microphone

Cf and Rf adjust the sensitivity of the input. A 1k resistor and 1uF
capacitor will give a reasonably OK filter for voice, I think. However,
playing around with different values will give you a different profile.
the function of attenuation with frequency is

a = Rf/sqrt(Rf^2+(1/(2*PI*f*Cf))^2) 

-- 
Regards,
   Robert Monsen
"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

Relevant Pages

  • Re: Scots send Lockerbie Bomber home
    ... long time..."My Big, Fat Greek Wedding" was a spoof, ... and their kids' kids are virtually identical. ... She didn't speak a word of English, ... different ethnicities. ...
    (soc.culture.scottish)
  • Re: Anti-pot PSAs
    ... It's the one where the black kids are ... they don't know how to speak in other situations. ... They are the lowest common denominator of the ... community and often the criminal element as well, ...
    (rec.arts.tv)
  • Re: Anti-pot PSAs
    ... It's the one where the black kids are all ... to speak in other situations. ... They are the lowest common denominator of the ... community and often the criminal element as well, ...
    (rec.arts.tv)
  • Re: Protocols of the Elders of Zion, Introduction
    ... demonstrated repeatedly with your constant snarling attacks, ... lashing out at someone's kids, it's time to admit defeat and try to ... And yes, I speak my own language, which makes me clever indeed. ... care how many of your cheesy, throwaway, cut-and-paste books you've ...
    (misc.writing)
  • English like wot she is spoke.
    ... A lot of the problem seems to stem from not being able to speak English ... "English" kids who just have such a poor grasp of the language. ... read them "cold" it won't matter so much. ...
    (uk.rec.sheds)