Hello all,

Im currently working on a project to design my own circuit but i am struggling.... alot!!

The circuit i wish to design is the following.
A noise (sound) indication box. There will be two lights on the box one green and one red.
The green light will illuminate if the sound is under 79dB.
If the noise goes to 80dB or over the red LED will illuminate.

I understand i will need a transducer to monitor the sound then the sound needs to be conditioned then converted to a digital format.

Any designs/ideas are welcome.

Thanks for taking the time to look.

 

Microphone or hi Z speaker, AC amplifier to give about 3 V PP signal, rectifier, filter, 2 comparators, 2 LED's.

 

...Any designs/ideas are welcome.

How complex is the sound? You likely need some "weighting" network that responds to the ratio of peaks to average levels. It is not simple.

What is the application?

 

LM3915 VU meter chip.
and/or
Microphone, amplifier, precision rectifier, comparator, LED
where the LM3915 chip might or might not be used for the comparator function.

 

Buy a sound level meter, set it for the correct range, attach to its output connector, comparator, LED.

 

IF you want to build something from scratch
AND IF the lights can be simple low power LEDs
AND IF you don't care about precision measurement, weighting factors, etc.

THEN:
Microphone > 1/2 LM358 opamp as preamp > diode, cap, resistor > 1/2 LM358 opamp as level detector > current limit resistor > Green LED to Vcc, Red LED to GND.

OR:
Microphone > 1/2 LM393 comparator as preamp > cap, resistor > 1/2 LM393 comparator as level detector > Red LED > Green LED to GND, current limit resistor to Vcc.

Power = 9 V battery.

ak