KasperNyhus said:I found this thread and had PRR reupload the schematic, but I dont fully understand it.
Is this correct?
Should the "?" pins from the LM339 be connected to ground?
Is it possible to supply it from +-5V?
And they are trying to sell more opamps... ;DPRR said:> The many parts part seems to be a rectifier which is nice but .... .... probably overkill.
That's stolen directly from old National Semi sheets.
Years ago I invested some time trying to make a cheap bi-color display that didn't suck. IMO signal present (green) does not need much help, with a low enough threshold it doesn't take much audio signal present to deliver a readable display, even half wave. The peak (red), OTOH does require significant hold time to not ignore brief transients or marginal signals.You need -some- form of filtering/averaging or (on speech/music) it is all flicker.
In my experience precision is not worth the effort/cost for simple A) is signal present in that path? and B) is the signal too hot?You want -some- form of semi-precision rectifier with reference levels likely around a half-volt.
I had to go back to look at what I did. My input Z is as low as 33k ohm and not perfectly linear. The input node labelled SMPLA is a common sample node where multiple diode cathodes combine together (diode or) with the individual diode anodes sampling levels at multiple circuit points. Only half wave but in my experience sampling at multiple circuit nodes "may" provide both polarities so full wave after a fashion.Many one-opamp half-wave plans exist. Some are just incredibly clever, even cute. Most have "some" drawback; low input Z, or different input Z for one side or the other. As you say, "don't interfere".
This stolen plan is just 2 opamps and has consistent 33K input any which way. In an unbalanced world, this is "just another load".
As you say, signal conversion may be part of the total problem, but extracting signals from different sources can become a whole other book-shelf than the blinky-light books.
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