LED Audio Signal Display

I am trying to accomplish the following and honestly have very little clue as to how to accomplish it.

Project goal:
Use the speaker (audio/AC) signal from a bluetooth headset to illuminate a single LED when a signal is preset. Preferably pulsing with the signal and possibly with adjustable sensitivity.

Considerations:
Size and power. Physical dimensions need to be as small as possible. Power source needs to be 3V or less, hopefully using button-type cells. Another consideration is that there is now only one good electronics supply house left in town. The easiest way for me to obtain parts in a timely manner is good 'ol Radio Shack.

Intended use:
I have a radar detector audio output connected to a bluetooth transmitter. I use a bluetooth receiver/speaker/mic headset especially designed for motorcycle helmet applications. The speaker volume is considerably louder then most cell phone or audio bluetooth headsets. I would like a visual indicator in the helmet as well. I do not want to attempt to modify any of the internals of the bluetooth transceiver, including tapping it for power. I would like the visual indicator circuit to be self contained for mounting inside the helmet or on the headset connector.

I hope this explains my needs clearly. I can solder, read schematics, and have a solid 12V electrical background. Unfortunately as professional 12V tech I always left the electronics repair and troubleshooting to the bench techs and never gained (or forgot) most basic electronics knowledge.

Any help would be greatly appreciated!

My idea: Just take the signal and use it to turn on an LED using an NPN Transistor. Led's don't even need 3V I don't think so it "should" work. Then you could have a variable pot to control the input (illumination point) and another for the brightness of the led.

I'm unclear as to how this would work. If I could be pointed to simple schematic that would be great. The LED requires 2V minimum and the best I can tell is the maximum voltage of the signal to the driver is about 5.5mV.

TrevorP said:

My idea: Just take the signal and use it to turn on an LED using an NPN Transistor. Led's don't even need 3V I don't think so it "should" work. Then you could have a variable pot to control the input (illumination point) and another for the brightness of the led.

Click to expand...

Ok here is the basis of my idea...although I forgot the potentiometer for after the signal.

The second one is a Darlington in case there wasn't enough amplification...but I doubt it would be needed.

Thanks. I did manage to figure it out on my own and it works fine with one exception. I used a BC547 and it works great with my test source (an old tape player) but the voltage from the headset must be lower as it needs to be at almost max. out to provide enough base voltage to illuminate the LED.

Is there a more suitable transistor?

TrevorP said:

Ok here is the basis of my idea...although I forgot the potentiometer for after the signal.

The second one is a Darlington in case there wasn't enough amplification...but I doubt it would be needed.

Click to expand...