Sensitive audio Transistor driven circuit.

Thread Starter

computerlen

Joined Nov 26, 2011
11
There are three resistors in this circuit but that doesn't matter. I had tried many times to wire up an LED driver circuit using only one or two transistors but never had luck. This circuit that I found on the web does work but I feel strongly that a transistor should be able to do the same thing- make a LED flash along with a low level audio signal. A dynamic microphone, for example. I really wish that I could figure out why I am having so much trouble in getting a simple transistor driven LED circuit to work. Thanks for any help you can give to me.
 

BobTPH

Joined Jun 5, 2013
9,189
There are three resistors in this circuit but that doesn't matter. I had tried many times to wire up an LED driver circuit using only one or two transistors but never had luck. This circuit that I found on the web does work but I feel strongly that a transistor should be able to do the same thing- make a LED flash along with a low level audio signal. A dynamic microphone, for example. I really wish that I could figure out why I am having so much trouble in getting a simple transistor driven LED circuit to work. Thanks for any help you can give to me.
Post a schematic.
 

KeithWalker

Joined Jul 10, 2017
3,147
There are three resistors in this circuit but that doesn't matter. I had tried many times to wire up an LED driver circuit using only one or two transistors but never had luck. This circuit that I found on the web does work but I feel strongly that a transistor should be able to do the same thing- make a LED flash along with a low level audio signal. A dynamic microphone, for example. I really wish that I could figure out why I am having so much trouble in getting a simple transistor driven LED circuit to work. Thanks for any help you can give to me.
For normal sound levels, the output of a dynamic microphone is only 2 or 3 mV. You would need a gain of several thousand to turn that into a LED signal. The output of an electret microphone is anywhere from 10 to 100 mV depending on the type.
 

Papabravo

Joined Feb 24, 2006
21,264
There are three resistors in this circuit but that doesn't matter. I had tried many times to wire up an LED driver circuit using only one or two transistors but never had luck. This circuit that I found on the web does work but I feel strongly that a transistor should be able to do the same thing- make a LED flash along with a low level audio signal. A dynamic microphone, for example. I really wish that I could figure out why I am having so much trouble in getting a simple transistor driven LED circuit to work. Thanks for any help you can give to me.
Forget the other two resistors, just reduce the 100Ω resistor that connects the LED to the battery. That will reduce the current in the LED. It may or may not produce the effect you are looking for. BTW I have NEVER seen anybody try to drive an LED through a capacitor. That might be a contributing factor to your difficulties. I guess there must be a first time for everything.

It just might help if you tell us what you are trying to do instead of telling us how you want to implement a solution. You seem to have some notions that are not feasible.
 

AnalogKid

Joined Aug 1, 2013
11,160
Please update your question. It is not clear what you want to achieve. Do you want the LED to flash when audio is above a certain loudness? Do you want the LED to stay lit continuously while audio is present? Other?

The LM386 is not a transistor. Do you want a different circuit that uses only transistors?

ak
 

Thread Starter

computerlen

Joined Nov 26, 2011
11
First off-this circuit above is what I found on the web. It DOES work. Forget about that circuit. I am in search of a circuit that uses transistors only that will drive an LED anytime there is audio spoken into a dynamic microphone.
 

sghioto

Joined Dec 31, 2017
5,421
First off-this circuit above is what I found on the web. It DOES work. Forget about that circuit. I am in search of a circuit that uses transistors only that will drive an LED anytime there is audio spoken into a dynamic microphone.
Try this circuit, only 0.5 ma on standby.
1706501909862.png
 
Last edited:

MisterBill2

Joined Jan 23, 2018
19,091
The LM386 circuit originally posted also needs a resistor from the input to common, in addition to the other parts required. At least 10K oms.
 
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