Sound activated LED's Help

[MartinTheGreat]

I am trying to figure out how to have a small mic in a circuit so when it picks up sound from around it, it lights up some LED's. I am thinking it has to be a switching circuit with 2 transistors.

If anyone can help me design a circuit, it would be appreciated.

 

[jimlovell777]

**broken link removed**

found here The Electronic Peasant's LED Flashlights and Multi-Color Displays Page

There are literally hundreds of designs out there, Google should pull them up.

 

[Hero999]

It depends on how many LEDs and whether you just need a simple flasher or something more complicated.

If it's a simple flasher, take a look at the thread linked below.

https://www.electro-tech-online.com/threads/plz-help-me-playing-with-these-leds.104377/

EDIT: Here's some schematics from the thread.
**broken link removed** **broken link removed**

 

[MartinTheGreat]

Hero999 that is pretty much exactly what I am looking for, but I am unsure how much power the tiny mic can put out. And what diode would I use between B-E

 

[ericgibbs]

Hero999 that is pretty much exactly what I am looking for, but I am unsure how much power the tiny mic can put out. And what diode would I use between B-E

hi,
That circuit input would require an audio signal of at least +0.65Vpk [or 1.3Vppk] before it would light the LED's.
You require a pre-amplifier to drive the LED driver transistor.

 

[MartinTheGreat]

You require a pre-amplifier to drive the LED driver transistor.

So that would require a 2nd transistor. I am just learning about them in school right now, so getting as much help on here as possible would be greatly appreciated.

 

[Hero999]

hi,
That circuit input would require an audio signal of at least +0.65Vpk [or 1.3Vppk] before it would light the LED's.
You require a pre-amplifier to drive the LED driver transistor.

Yes, you're right, that circuit's for a walkman or CD player headphone output. I'd forgotten the idea was to use a microphone.

Using a Schottky diode will make it slightly more sensitive about 450mV peak but it still isn't good enough you need another transistor to amplify the signal enough to drive it.

 

[MartinTheGreat]

Hero999, the 220 ohm resistor, that would be for 2 LED's but with what forward voltage were you using? I have a few LED's that have a forward voltage of 3 - 3.5V.

Please forgive my ignorance.

 

[ericgibbs]

Hero999, the 220 ohm resistor, that would be for 2 LED's but with what forward voltage were you using? I have a few LED's that have a forward voltage of 3 - 3.5V.

Please forgive my ignorance.

hi,
Using a 9V source, connect only two of your LED's in the collector circuit.
If your LED's are rated at say 20mA, the series resistor will have to drop approx 3 volts at 20mA.
So taking the LED's at 3Vdrop, thats [9V-6V]/0.02 = 150R for 20mA and 300R for 10mA thru the LEDs.

If you wanted to drive say 4 LED's use a 150R or 300R for each pair.

Do you follow.?

Is your microphone an electret type.?

 

[Hero999]

I wouldn't recommend using two 3.5V LEDs in series because when the voltage drops below about 8V, they'll barely light.

The circuit above is designed for red LEDs which will have a voltage drop of about 1.8V or 3.6V which wired in series. The peak current will be 24mA but the LEDs will only be on half the time to the average current is half that.

For 3.5V LEDs, you can just connect them between the collector and +v, each with their own 220R resistor.

 

[Reloadron]

If you want to venture into making things interesting several circuits can be found here. The circuits can be modified to drive LEDs and also have different colors respond to different frequencies of the audio.

Many years ago I built one such circuit to drive my Christmas tree when I was single. I had the Reds respond to bass, the Greens to mid range and the Blue to treble. Pretty cool back then but using incandescent bulbs.

Anyway, the link may provide some thoughts. Additionally a Google of "Color Organ Circuits" will bring up some good hits.

Ron