Sequencer Update

[List, Christopher]

> -----Original Message-----
> From:	jhaible [SMTP:jhaible at metronet.de]
> Sent:	Wednesday, August 19, 1998 8:04 PM
> To:	DIY
> Subject:	AW: Re: Sequencer Update
> 
> > I didn't know about this circuit when I built my sequencer, and
> > used the "brute force" 16 comparator + 2 encoders method for my 4bit
> > flash ADC. 
> 
> Chris, do you have the circuit for this one at hand? Have spent a few
> thoughts about economic encoding, but haven't come up with anything
> convincing yet. Are
> there speacial chips for that? (Four LM324s, or LM339s, for the
> comparators is no
> problem.)
> 
	I went through my files last night to see if I had a protobaord
layout for it, but - like most heavy CMOS logic chip circuits, it didn't
lend itself to protoboard very well, so I just did it all on the fly. I
used a FWR in front of the circuit, then four 339's for the comparators.
A chain of (16) 1K resistors + a 20K trimmer set the reference voltages.
The outputs of the 339s go to a pair of CD4532B 8bit encoders, and these
have to get hooked together in a funky way with a quad AND gate in the
middle (I used a MC14071B). The data sheet for the 4532 shows the hook
up.

	This setup clocks the sequencer pretty well way up into the
10kHz range or so - with the big problems for high speeds coming from
the comparator switching time and the shape of the input waveforms.

	As you said, though, I think just a two bit ADC should do it for
you, or maybe three bit to select from your horizontal - either way your
chip count goes way down!

	Have you planned out the Octave + Semitone quantizer yet?
Unfortunately, there doesn't seem to be anyplace online with the full
catalog of 4000 series datasheets (someone please correct me if I'm
wrong) . Harris requires faxing for those chips, and Fairchild doesn't
have everything listed. I'm curious to hear about your part selection
for this, as it's a cool idea. It'd be great if there were something
like 4017 but with 12 stages - that'd make things very easy! Another
thing that would be cool for this would be if you could latch the
12-step counter value with the latch triggers by any of your quantizer
comparators (I assume you'd have one for each row) and run the result to
another mux driving LED's. You could set up the 12 switches along the
bottom of the module in the shape of a little keyboard with LEDs under
each key and see which notes you're playing with your sequence! Talk
about high parts count for the sake of pretty lights! 

C.List
chris.list at sc.siemens.com