Condenser Microphone Max Voltage Output problem need help

[gurunz]

coupling capacitor condenser audio output mic pre

hi all
now im creating a project for my final year named gunshot range detector.
I have a problem to capture output voltage from microphone when gunshot detected. My system use Bandpass Filter that filter of Fc= 3kHz and voltage peak detector to change AC signal to DC signal. After that i use PIC 16F877a to calculate the range of gunshot. My equation is when input voltage is 5V(loudest gunshot),lcd will display 20m distance, and the distance increase as voltage decrease until 1V equal to 100m.
I succeed in simulate the circuit in proteus with AC input but after i done my prototype, when i test it with real gunshot sound, the result is dissapointed. Hope someone can help me

Thanks alot

 

[Audioguru]

condenser microphone voltage peak

The input pin 3 of your 741 opamp is 0V so it will not work. Since you have a single supply voltage then the opamp input must be at half the supply voltage.

The lousy old 741 opamp was designed to use a 30V supply and will not work from a supply as low as 5V.

The bandpass filter must be fed from a very low impedance like the output of an opamp. But its input impedance is too low to be fed from an opamp.


You probably have an electret microphone, not a condenser microphone. The microphone must be powered and it will probably be overloaded with the high sound level from a gun.

Your LM358 dual opamp is doing nothing. It has no gain and the value of R4 is so high that it will barely work. R5 and R6 are doing nothing.
You should use an active rectifier circuit to avoid the 0.6V loss of the rectifier diode.

Why do you have a bandpass filter? A gunshot sound is wideband and is mostly very low frequencies. 3kHz is attenuated by the ground at a distance.

 

[gurunz]

elektret mic circuit opamp 741

thanks audioguru for help,i am very appreciate it

so,my whole circuit is totally useless,hmmm...i wonder why its nothing wrong when i simulate the circuit in proteus..that why i believe my circuit will work properly. If u dont mind audioguru, i really hope to know ur own recommendation to make my circuit work well. I am really really thankful for your help.

Added after 10 minutes:

n for your information, i use LM741CN opamp as bandpass filter and use multiple feedback Bandpass Filter method.I use LM358N for voltage peak detector.

 

[Audioguru]

how much voltage is generated by a mic

The input common-mode voltage range of an opamp is the voltages where the inputs work.
For the 741 opamp it is 3V above the negative supply and 3V less than the positive supply. So with a 6V supply the inputs barely work if they are biased at half the supply voltage. It will not work with a supply that is only 5V.

When the supply is only 6V the output of a 741 opamp can swing only 2V peak-to-peak when the load current is very low (10k ohms load).

The datasheet for a 741 opamp shows that the open-loop gain is 200,000 with a 30V supply and drops to only 40,000 with a 6V supply.

An active rectifier circuit needs to have an input that swings below 0V. So a coupling capacitor is needed between the output of the bandpass filter and the input of the active rectifier circuit.
The rectifier diode is included inside the negative feedback loop for the opamp to cancel the forward voltage drop of the diode. The active rectifier circuit uses an inverting opamp.

Are you using an electret microphone?
Why are you using a bandpass filter?
Why is the frequency of the bandpass filter set so high?

 

[gurunz]

condenser mic bandpass filter

I thought to use it but in my place the electronic shop just sold condenser microphone but i will try to buy online.
I use bandpass filter because i want to capture voltage on certain frequency and i choose 3 kHz bandpass because from my research on gunshot detection, gunshot sound is identified by its muzzle blast and the frequency range of that muzzle blast is between 2KHz - 3 kHz. At muzzle blast itself has maximum amplitude of gunshot sound that can be implement to detect the range of gunshot.

If i use lowpass filter, i fear that my circuit can't differentiate between gunshot sound and other sounds.

 

[Audioguru]

microphone max

I think your electronics shop doesn't know the difference between a condenser mic and an electret mic.

A condenser mic needs a very high input impedance preamp and a 48V supply.

An electret mic has a FET transistor as an impedance converter built-in and it has the 48V built-in. The FET needs a few volts at 0.5mA.

Thunder from lightning is similar to a gunshot sound. The high frequencies (above 200Hz) are absorbed by the ground at a distance so the sound is just low frequency rumbling. The same for a gunshot sound.

 

[gurunz]

simple condenser mic circuit

Hahaha..that rite..i have already search at all top electronic shop in my country but they keep saying we didnt have electrect mic la,just use condenser mic
ooo..so my assumption of 3khz for gunshot sound max amplitude isnt correct.Do u have suggestion what filter should i use so my project can identified gunshot sound and same time detect highest amplitude?

 

[Audioguru]

low pass 741 3khz

The guns that I have heard are much louder than background noise. Don't use a filter.

I use TL071 single, TL072 dual and TL074 quad opamps for audio. They are low noise, very low distortion and have a bandwidth to 100kHz.
They don't need a regulated supply and work well from a new 9V alkaline battery when the input is biased at half the supply voltage. their minimum supply is 7V. There are newer and better audio opamps available today.

The lousy old 741 opamp was designed 41 years ago and was used for DC and low frequencies. It is noisy and has a bandwidth to only 9khz.

 

[gurunz]

condenser mic peeking

wauu id didnt know there are another better op amp of lm741 because i just learn using lm741 only.hopefully they sell ti071 here.
Another question audioguru,actually my main question, how we want to know what the output voltage generated when certain level of sound is capture. As example what voltage produce when 86dB sound captured?Is there any table for that decible to voltage conversion?

 

[Audioguru]

microphone voltage

how we want to know what the output voltage generated when certain level of sound is capture. As example what voltage produce when 86dB sound captured?Is there any table for that decible to voltage conversion?

1) Look at the datasheet for your electret microphone. Its sensitivity will be listed.
2) Make the gain of the preamp as high as is necessary for the peak output to be as high as you want.
3) Use a supply voltage that is high enough for the output to go as high as you want.