Sound Level Indicator.

Guest
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.
Thanks, Raul
 
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
Click to expand...
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.
 
HI Raul:

Try using just an amplifier and a microphone. Instead of using a
speaker, just use a 12v tail light from the auto store. These are
typically 4 to 12 ohms equivalent to an 8ohm speaker. As the student
talks, the light will glow. Pretty simple.
Harold
 
I'm sorry I can't read the ANSI schematic. I am a novice. If I have a
schematic I can use my bread board to get it to work, then build it. I
can't do it from the ANSI drawing. I'm not that good. Is there some way
I can convert it to a regular schematic?

Thanks, Raul
 
<raul@2minclip.biz> wrote in message
news:1106480360.902786.311710@z14g2000cwz.googlegroups.com...
I'm sorry I can't read the ANSI schematic. I am a novice. If I have a
schematic I can use my bread board to get it to work, then build it. I
can't do it from the ANSI drawing. I'm not that good. Is there some way
I can convert it to a regular schematic?

Thanks, Raul
Click to expand...
Use the full screen and select a fixed width font such as courier.
 
Thanks a lot. I'll will try and build it. I'd rather do that than just
buy something. You don't learn much that way. I'll put up pics when
I've got it working.
Thanks, again
Raul
 
raul@2minclip.biz wrote:

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.
Thanks, Raul

use a quodd Op-amp chip, something like a LM324.
Click to expand...
using 3 OP-amps as the level LED's. use feed back
diodes to kill null the Op-AMp before that if you
wish only to have 1 LED on at a time.
use the last Op-Amp as the Mic preamp, the output of which
will be driving comparators.
P.S.
they do make LED bar graph segment display chips that give
you a solid or dot option display.
LM3916
http://www.national.com/ds/LM/LM3916.pdf
http://wiredworld.tripod.com/tronics/audio_level.html
 
<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.
Click to expand...
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
--
Click to expand...
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
 
On 22 Jan 2005 07:27:02 -0800, raul@2minclip.biz wrote:

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.
Thanks, Raul
Click to expand...
You might want to look into the inexpensive sound level
meters that Radio Shack sells. They are calibrated to
read in dB SPL and they have weighting scales so you
can use an A-weighted response that is roughly the way
your ear weights different frequencies. They also have some sort of
a peak-hold function, which I believe is what you want here,
but I'm not sure of the details. They also have analog
and digital models. Might be worth a look.


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
 
raul@2minclip.biz wrote:
I'm sorry I can't read the ANSI schematic. I am a novice. If I have a
schematic I can use my bread board to get it to work, then build it. I
can't do it from the ANSI drawing. I'm not that good. Is there some way
I can convert it to a regular schematic?

Thanks, Raul
Click to expand...
Here you go:

schematic: http://home.comcast.net/~rcmonsen/schematic.gif
PCB layout: http://home.comcast.net/~rcmonsen/layout.jpg

I haven't built the layout, I just drew it. It is for a single sided PC
board. Flip it left<->right, shrink it to 50%, and it should be OK. The
thick lines are traces, the thin lines are components, and the circles
are drilled holes. (Note there is a mistake in the resistor values below
the layout, R2 should be 10k, it seems to work better for me. The
schematic gets it right.)

Also, I added the 'red' led, DL2, on the fly without testing it. I think
it'll be ok.

I don't know how well it will work for you. However, the parts will be
less than $10 at RadioShack, I think, including an enclosure. You may
want to build it first on a solderless breadboard just to get a feel for
it. The pots adjust the sensitivity and the time the green LED is on
after being activated.

If you don't want to make a PC board, you can use stripboard, and type
the schematic into "StripBoard Magic" (which is available on the web
somplace). That may be easier, but you'll have to get some stripboard.
RadioShack usually doesn't carry it.

Bob Masta's suggestion, to buy something premade, will clearly be a
safer/easier option, in that it's guaranteed to work.

If you build it, let me know how it works out.

--
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.
 
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