moamps said:
That's the idea, but I think in your circuit the window is always +/- .6V, independent of the pot. That's a pretty wide window for offset. I think that if you want to make the window variable (although I see no need for it), you need two pots, each across the diode and feed the fractional diode voltage to the comparator inputs.
You may also want to add a small positive feedback across the comparator to introduce some hysteresis, to avoid oscillations around the switching point.
You may also want to put R7, R9 in series with the comparator outputs to limit the LED current.
Lastly, place diodes across the LEDs in opposite polarity to avoid destroying them with too much reverse voltage.
Jan Didden
I'm sorry, but this won't work (I might be wrong).
1 LP-filter, preferable up to 3th or even 4th order, cut frequency 0.01-1 Hz. Those filters most also have low offset voltages. This is dependent how low DC voltage you want to detect, how advanced the filter should be.
2 Fullwave rectifier or two halfway rectifiers, one for positive and one for negative signals
3 Comparator with HYSTERESES!
4 Indicators
Filtering out a couple of millivolts from several volts or tenths of volts is a tricky business. Don't forget that DC is low frequency AC!
1 LP-filter, preferable up to 3th or even 4th order, cut frequency 0.01-1 Hz. Those filters most also have low offset voltages. This is dependent how low DC voltage you want to detect, how advanced the filter should be.
2 Fullwave rectifier or two halfway rectifiers, one for positive and one for negative signals
3 Comparator with HYSTERESES!
4 Indicators
Filtering out a couple of millivolts from several volts or tenths of volts is a tricky business. Don't forget that DC is low frequency AC!
peranders said:
Not different from 'normal' servo loops. The fact that they are used in many 10.000's of amps is some indication that most probably it works. I concede that often the implementation isn't very good, but we have beaten that particular horse to death in this thread I would think.
Jan Didden
peranders said:
You obviously have not taken my advice to read the former posts. The servo loop is not closed, because he wants to regulate the offset by hand. I said "an integrator LIKE the servo loop NORMALLY used to....". There is no closed servo loop and the integrator output is the offset voltage, at least above the low pass freq. And indeed that should be low enough so that there is no lf audio to slowly vary the apparent offset.
Can I go now?
Jan Didden
Here's some initial doodlings of my linear idea
This is meant to be implemented with a quad op amp. The first section is a differential integrator which will probably change - I drew it this way because I wanted to be able to select this circuit as a bias monitor as well as a offset monitor circuit. The second and third op amp sections and associated components comprise a high speed 'ideal' full wave rectifier. The final op amp stage acts as a bipolar current source to linearly control the LEDs intensity. 'Off' would correspond to 0 volts offset, in this case. I threw in D5 and R16 to limit sensitivity more than several tenths of to a couple volts away from the null range. All component values hypothetical
This is meant to be implemented with a quad op amp. The first section is a differential integrator which will probably change - I drew it this way because I wanted to be able to select this circuit as a bias monitor as well as a offset monitor circuit. The second and third op amp sections and associated components comprise a high speed 'ideal' full wave rectifier. The final op amp stage acts as a bipolar current source to linearly control the LEDs intensity. 'Off' would correspond to 0 volts offset, in this case. I threw in D5 and R16 to limit sensitivity more than several tenths of to a couple volts away from the null range. All component values hypothetical
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