[sdiy] Bar Graph Driver as Quantanizer

[harrybissell at wowway.com]

You cannot just add these chips in series... the resistor strings internal
are well matched (ratio) but the absolute values can be way off. MAke a
precision resistive divider, buffered with opamps, and drive the nodes where
one string stops and the next begins

H^) harry




On Sun, 01 Feb 2009 10:35:18 -0500, rdrake wrote
> check out Grant Richter's Analog Tracking Generator...
http://www.musicsynthesizer.com/DIY/Grant/CVtwister.html
> 
> bbob
> www.fluxmonkey.com
> 
> >----- ------- Original Message ------- -----
> >From: :lightburnx at yahoo.com
> >To: synth-diy at dropmix.xs4all.nl
> >Sent: Sat, 31 Jan 2009 -0800 (PST) 20:00:45
> >
> >Some musings...
> >
> >While looking at the LM3914, a bar/dot graph
> >driver, I realized that it's basically a
> >quantinizer. With a few tweaks and a stable voltage
> >reference, it'd serve as such. I think... Help me
> >here if otherwise.
> >
> >Datasheet's here for reference:
> >http://www.national.com/ds/LM/LM3914.pdf
> >
> >One big question, is how could I use just 2
> >chips(*) for several octaves (vs. 1 chip per 10
> >notes...?). Some kind of dynamic reference voltage
> >offset...? Not unless that's not a completely
> >unreasonable solution. The datasheet says you can
> >chain together up to 100 outputs. With 12 discrete
> >keys per octave, that's 100/12 = effectively 8
> >octaves.
> >
> >(*) At least 2 chips would have to be employed
> >anyway, as they only have 10 outputs each. So, call
> >it 2 chained ICs for 20 total outputs, 12 of which
> >would be used for 12 "bits" of resolution/levels of
> >quantification. That's assuming the "just 2 chips"
> >configuration is possible, otherwise it's just a
> >step-after-another progression.
> >
> >There's also the LP3943, which has 16 outputs to
> >start with. It's a low power IC though - has that
> >any share of potential issues?
> >
> >Datasheet: http://www.national.com/ds/LP/LP3943.pdf
> >
> >
> >
> >The 3194 has a 'bar' and 'dot' mode; bar is 'from
> >ground up,' with each output giving a fixed
> >voltage, which when summed would give you the
> >quantinized CV.
> >
> >Switch to dot mode, which triggers the output
> >designated closest to the input voltage, and you
> >got a voltage controlled event generator; between
> >your preset step range (dunno the exact hysteresis
> >thereof...), gate 'a' fires, next step gate 'b',
> >etc.
> >
> >On the note of hysteresis, I looked it up in the
> >datasheet just now and it said there isn't any
> >built in, and there's a fadeover of 1mV or more
> >between outputs (apparently less if the next "step"
> >isn't on the same IC, for chained circuits). I'm
> >not sure how to address that... A comparator, or a
> >specific output-voltage referenced Schmitt trigger,
> >per output??
> >(x12 is kinda steep). How many cents off would ~1mV
> >bend a VCO anyway?
> >
> >Any other thoughts on this? And again, is it even
> >an effective, let alone feasible idea? Just wana
> >scope things out before I hit the breadboard.
> >
> >
> >Also: a grateful if belated thank you to everyone
> >who responded about my MS-20 filter clone
> >questions!
> >
> >
> >_Kyle
> >
> >
> >      
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Harry Bissell & Nora Abdullah 4eva