/diy/ - Do It Yourself

>>1746351

If you wanted to bolt an active node onto the output of something that was out of phase, a differentiator is one way you could do it, it looked 90º out-of-phase to me. You could also change the phase of the unfiltered input waveform. What matters is that they match when you feed those into a difference node which will subtract one from the other. The last op-amp in your LM324 can be used as a comparator to detect the presence/absence of whatever you are looking for. You could place a capacitor (or RC) in the input to the comparator to "hold" (as in sample-and-hold) the detect threshold. At that point, you might not need the µC.

This kind of reminds me of those 2D VU meter applications where it will give you the relative power across the spectrum, except you're looking at the lowest frequency band, and only one led high. Anyone remember chaining lm311s together to make a VU meter?

All this is to avoid a lot of complicated stuff on the µ controller side (obviously you could store a running window of values in memory, figure out how far back you need to look to compare, etc.

Not trying to make this complicated, it's all been done before.