beginners. some help with sound sensor (lm386+microcontollers)

[audioguru]

Yes, the 2.2k resistor reduces the sensitivity of the mic.
The peak detector will not work if you use R7 and C6.

 

[berumin]

Yes, the 2.2k resistor reduces the sensitivity of the mic.
The peak detector will not work if you use R7 and C6.

2.2k and resistance of mic (~1k) - voltage divisor
for 2.2k/1k - on mic will be about 1.5v
if i use 10k - on mic will be 0.5v
what i don't understand ? ;-)

...
so,
i need only change r1 ?

why i can't use lowpass filter (r7/c6) together peak detector (diode/c7) ?
if i can't use after lm386 lowpass and peak together, can I place lowpass before lm386 ?
or i must use another type of filter - for sample, band-pass ?

 

[audioguru]

The 2.2k resistor that powers the electret mic is the drain load resistor for the FET transistor inside the mic. The gain of the FET is much higher when the drain load resistor is 10k.

If you want to cut high frequencies then add a capacitor parallel with the mic.

 

[berumin]

The 2.2k resistor that powers the electret mic is the drain load resistor for the FET transistor inside the mic. The gain of the FET is much higher when the drain load resistor is 10k.

If you want to cut high frequencies then add a capacitor parallel with the mic.

simple parallel ?
and in calculate frequency in formula f=1/(2*Pi*RC) what resistance i must use (calc) ? R1 ?
if r1 = 10kom - C for freq=16khz = 0.001uF ?

 

[audioguru]

With a 9V supply, I measured the impedance of my electret mic to be 4.7k when it was powered from a series 10k resistor.
Then the mic and 10k resistor are a total impedance of 3.2k ohms.

For a 16kHz cutoff frequency use a capacitor parallel to the mic with a value of 3.1nF. Use a standard value of 3.0nF or 3.3nF.

 

[berumin]

With a 9V supply, I measured the impedance of my electret mic to be 4.7k when it was powered from a series 10k resistor.
Then the mic and 10k resistor are a total impedance of 3.2k ohms.

sorry.. i dont understand

mic and power resistor in series, but "new" capacitor will be parallely with only mic ?

my mic without power - 1.3kom, and my power in board will be 5V

For a 16kHz cutoff frequency use a capacitor parallel to the mic with a value of 3.1nF. Use a standard value of 3.0nF or 3.3nF.

 

[audioguru]

R1 in your circuit should be 10k ohms and R2 should be 1k.
Then a 3.0nF or 3.3nF capacitor should be in parallel with the mic.

The mic and R1 are in parallel for the signal.

 

[berumin]

R1 in your circuit should be 10k ohms and R2 should be 1k.
Then a 3.0nF or 3.3nF capacitor should be in parallel with the mic.

The mic and R1 are in parallel for the signal.

ok, thks!
i will try to design and assemble proto-board

i find mic
https://www.image.micros.com.pl/_dane_techniczne_auto/mipkpcm29b.jpg
but on sample - used 2.2k resistor - not 10kOm

if I change 10kOm (suggested by You) to 2.2 kOm - i need change capacitor parallel with the mic to 0.01uF ?

 

[audioguru]

The mic datasheet you posted does not show its typical impedance, only its max impedance. Then you will not be able to use a capacitor in parallel as a lowpass filter because the cutoff frequency will be unknown.

They show a 2k resistor powering the mic from a 4.5V supply. If the current in the mic is 400uA then it will have a voltage of 3.7V across it. With a 9V supply if the current in the mic is 450uA and the resistors feeding it total 11k ohms then the mic has 4.05V across it.

 

[berumin]

The mic datasheet you posted does not show its typical impedance, only its max impedance. Then you will not be able to use a capacitor in parallel as a lowpass filter because the cutoff frequency will be unknown.

They show a 2k resistor powering the mic from a 4.5V supply. If the current in the mic is 400uA then it will have a voltage of 3.7V across it. With a 9V supply if the current in the mic is 450uA and the resistors feeding it total 11k ohms then the mic has 4.05V across it.

without power - mic show 1kOm impendance
my power is 5v, not 9v

 

[audioguru]

I was guessing that the powered impedance of your mic is 1k ohms. It is parallel to the 2.2k resistor that powers it from 5V so a capacitor with a value of 14.5nF parallel to the mic will result in a lowpass filter with a cutoff frequency of 16khz.