Help detecting if sine wave is present.

Basically, I want to drive a load when there is an input of <150hz, and be off when the frequency is higher, or no input at all.

My idea was to pass the input signal through a lowpass filter, then have something turn on when the peak-to-peak voltage is over x-volts.

Thanks

How do you plan to generate the 150hz ?

Do you have an high quality DMM with frequency counter ?

I have a frequency counter. The 150hz doesn't need to be exact. I'm going to be driving LED's to the bass of music. The problem with just using the sine wave from the audio signal is that I will only be using half of the wave to power the LED's.

Look up "missing pulse detector" It's just a one-shot that is held in reset by incoming pulses. If set up for T~=1/150, then it could detect when the frequency changes. That should give better results than a filter, IMO.

EDIT: I didn't see your last post. Since you're doing audio, there are much better methods. Try a key-word search on ETO. There have been some pretty good circuits posted over the last several months/years.

A LPF along with an LM3915 would do what you want. Eric Gibbs even wrote a 3M3915 calculator program.
https://www.electro-tech-online.com/blogs/ericgibbs/135-basic-lm3915-calculator-v3-0.html