Sound Frequency-based power redirect

Thread Starter


Joined Nov 12, 2014
I am working on a project and really don't know where to begin. Wondered if you might point me in the right direction.

What if I had a microphone of some sort, a power supply, a switch and 2 LED banks (red & blue) and I wanted the power to flow to one LED bank (red) or the other (blue) based on sound frequency? So any sound below 146.8Hz directs my power source to the red LEDs and anything above 146.8Hz powers the blue LEDs. No sound = no power to either.

Any thoughts where I might start looking to develop a solution? Would even be willing to pay someone to help me or to simply design it and give me schematic and parts list.

Thanks in advance.


Joined Nov 29, 2005
Is the audio signal a single frequency or is it music ?
For a single frequency, I would suggest a VOX circuit. When there is audio, enables or supplies power to a frequency-to-voltage converter, like a LM2907 in speed switch mode. Perhaps its data sheet allows fine-tuning the tight crossover frequency to your needs.
A sharper circuit would take a portion of a precision PLL oscillator tapping its over/under correction signal to drive the leds.
A well tailored NE567 can come very close to the exact crossover signal detection monitoring pin 2, but won't be easy beyond a large frequency span.

blocco a spirale

Joined Jun 18, 2008
If this is going in a guitar it will have to deal with frequencies above and below 146.8Hz (D) simultaneously even if you play a note with a fundamental frequency of less than 146.8Hz. e.g. If you were to play a C at 130.8Hz the fundamental will cause the Red LEDs to light and the harmonics will cause the blue LEDs to light.

What exactly is the purpose of this circuit?