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Old 23rd July 2010, 06:56 PM   #1
AuroraB is offline AuroraB  Norway
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Question Vector meter - or steering indicator

A friend of mine asked me to help him with ideas for a LED based intensity steering indicator , -- something like a simple LED based vector meter...
But I'm just too stressed out with my own work these days - I just cannot wrap my head around this one....

What he needs is a sort of steering indicator, where equal loudness in both channels gives a center reading - and levels shifting left or right moves a LED dot left or right on a 10-15 dB LED scale.
A zero center analog meter would also do the trick.....
I just cannot find anything on the net either.......

Ideas anyone - or some links ??????

TIA!
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Last edited by AuroraB; 23rd July 2010 at 06:58 PM.
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Old 24th July 2010, 01:19 AM   #2
star882 is offline star882  United States
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PIC with two A/D channels driving an array of LEDs.
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Old 24th July 2010, 02:59 AM   #3
gootee is offline gootee  United States
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Or, if you wanted to go all analog: Start with an opamp configured as a difference amplifier, subtracting one channel from the other (say right minus left). That would give a positive output for right > left and a negative output for left > right. Then split into two paths, one for the left-side LEDs and one for the right: Have a schottky or other diode in each path, in series, pointing the right direction to only let current through for the correct polarity, and then a resistor to ground after each diode. Take your levels from there (from across each resistor) and use a standard "diode string level-meter" IC for each side (see national.com). I guess you might have to use an inverting unity-gain opamp amplifier on the negative side, first. And you might have to twiddle with some resistive dividers or opamp amplfiers to get the voltages to come out right for full-scale levels, etc. For the center LED, you might have to take the two levels, i.e. from after the two diodes (or from after the "positive" side diode and the "negative" side inverting amplifier), and put them through a two-input inverted OR gate, so it would light when neither level was high-enough to get past its diode. You might have to condition the two inputs for that gate, maybe with comparators (or opamps wired as comparators), to at least keep them below the max allowable voltage for the OR gate's inputs, but probably also to always put them into the "1" range if they got anything at all past the diodes (or, actually, if they got enough past their diode to light the first LED). [You could also use two "ideal diode" one-opamp circuits, instead of two simple diodes, if the 0.3 volts or so that would be lost with the schottkys became inconvenient, somehow.] Later, you might also want to do some smoothing or averaging. So you might want to allow for having a simple series R and C to ground, before the two "level" outputs. And, instead of an IC made for lighting a diode string to indicate a level, you could just use a set of windowing comparator circuits for each side. (Using the zero-center analog meter instead of LEDs might eliminate most of that circuitry. You might then need only the difference amp.)

That's all just off the top of my head. So some or all of it might be wrong. And there might be a lot of better ways to do it. You could download LTspice from linear.com and just try it, or, do a paper design and then build, test, tweak.

Application Notes AN-20 and AN-31, from national.com, should have everything you need, for the opamp parts of the circuit.

Last edited by gootee; 24th July 2010 at 03:17 AM.
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