LM386 Mic Amp to LED Output

[audioguru]

well after i change the 22k to 47k this circuit sounds better...

My resistor values were calculated for a 9V supply. If your supply is only 5V then they need to be changed.
"Sounds better??" The circuit turns on an LED when there is sound at the mic. It is not designed to produce an audio output since its output is DC not AC.

but now im facing the receiver error part as it does not receive any signal to "on" my PIC...

There is no receiver. The circuit is just an amplifier to light an LED.
The output is a max voltage of about +7.3VDC when the supply is 9V.
The max output is about +3.3V when the supply is 5V.

 

[disney_snoopy]

hmmm... i use the 47k for my 5V... can i know how does u design or calculate out the resistor value?

Actually my output is not an audio but is to trigger a high voltage for my PIC as input of my PIC. So this circuit does trigger more than 2.4V from the LED and flow to my PIC input. Hence, my PIC output does trigger as i put an LED on the output PIC port.

The only problem is my receiver part cant get the signal... i was not sure whether it is my transmitter problem or the receiver PIC programming problem...

 

[audioguru]

With a supply of only 5V then you do not need the two resistors at pin 2 of the LM386. Remove the two resistors and the amplifier will be more sensitive.

 

[disney_snoopy]

With a supply of only 5V then you do not need the two resistors at pin 2 of the LM386. Remove the two resistors and the amplifier will be more sensitive.

hi sir,

the two resistor that u call me to remove, i remove and i found that it was too sensitive and cause my RX side output always on.

 

[flat5]

Deleted...twice.

 

[audioguru]

hi sir,

the two resistor that u call me to remove, i remove and i found that it was too sensitive and cause my RX side output always on.

This is what i said before, "The part at pin 3 is not a resistor, it is a variable resistor which is called a volume control. It adjusts and reduces the input level so that the LED is not turned on all the time".

 

[disney_snoopy]

oh... i get what u mean alr...

However, the 1k and 10k that is above the microphone is for sensitivity also?
or any reason for putting this resistor?

 

[audioguru]

the 1k and 10k that is above the microphone is for sensitivity also?
or any reason for putting this resistor?

The 10k resistor powers the FET transistor inside the electret mic.
The 1k resistor and 100uF capacitor decouple the supply to the mic so that there is no low frequency positive feedback.

If the 10k resistor value is less than about 4.7k then the sensitivity of the mic will be reduced. If it is more than about 22k then loud sounds might be distorted by the mic.

With the 10uF capacitor at pin 1 and pin 8 of the LM386 IC then its gain is 200.

 

[disney_snoopy]

If the 10k resistor value is less than about 4.7k then the sensitivity of the mic will be reduced. If it is more than about 22k then loud sounds might be distorted by the mic.

sorry. i still doesnt get what does u mean as in this circuit there is no 4.7kOhm.
It only have 47k but i have replaced it by 22kOhm. Can explain further???

Anyhow how to calculate the gain in theoretical?
As i find book it does have a formula

Gain = 30k/ (150 + ((1350 x R)/(1350 + R)))

However, can tell me where is the 30k, 150, 1350 come from? Im very blur of this...

 

[audioguru]

sorry. i still doesnt get what does u mean as in this circuit there is no 4.7kOhm.

You don't understand technical talk.

It only have 47k but i have replaced it by 22kOhm. Can explain further???

Use 47k.

Anyhow how to calculate the gain in theoretical?
As i find book it does have a formula

Gain = 30k/ (150 + ((1350 x R)/(1350 + R)))

However, can tell me where is the 30k, 150, 1350 come from? Im very blur of this...

The datasheet for the LM386 shows its schematic and the 15k, 1350 and 150 ohm resistors that determine its gain. I was wrong before, its DC gain is 20, not 10. The datasheet for the LM380 explains why its gain is twice as high as calculated.

Since it does not drive an LED in your application I reduced the values of its capacitors and used a 100k load resistor.