[sdiy] Sequencer Idea

[John L Marshall]

Originally I was looking at a 74x154 then I noticed that getting the signals
back together again was a real chore. The 74x159 is open collector so only
one output will be low at a time. All other outputs will be floating so I
think that makes the outputs of the thumbwheel switches a giant wired or. At
least I hope so.

John


----- Original Message -----
From: René Schmitz <uzs159 at uni-bonn.de>
To: John L Marshall <john.l.marshall at gte.net>; <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, October 03, 2001 12:07 PM
Subject: Re: [sdiy] Sequencer Idea


At 23:16 02.10.01 -0700, John L Marshall wrote:
>I just bought 288 BCD thumbwheel switches for $20. I figure that I can
build
>a really big, easy to program, sequencer using the thumbwheel switches.
Here
>is the plan:
>
>Build a 48 step sequencer using 48 thumbwheel switches. The thumbwheel
>switches point to a 4x10 bank of pots. Four control voltages are available
>but there will only be ten unique sets. My experience is that longer
>sequences often repeat sounds. Ten unique sounds for a 48 step sequence
>probably works.
>
>1. Clock drives usual divider chain.
>2.  Divider chain drives 3 each 74x159 (open collector) four line to 16
line
>demultiplexer.
>3. Each demux output connects to  it's own BCD thumbwheel switch.
>4. The BCD lines are all tied together and routed to an open collector BCD
>decoder.
>5. The BCD decoder is connected to a 4x10 bank of pots.
>6. The rest is the usual analog stuff.
>
> Comments?
>

Thats an idea that I have had on my mind for some time now.
I want to do 2x16 and just use 8 different levels (My switches are octal).
But both rows will operate independantly of each other.
I want to use CMOS multiplexers for the analog part instead of a binary
decoder, so I could use the same set of voltages for both rows, or two
independant sets just by enabling the respective multiplexers.
But what you describe would work too.

Whats nice about this is that the levels are ganged, as you change a level
all other notes of that value are automagically changing as well.

I think to make the BCD switches work independantly one needs to
make a wide OR gate, or else the bit lines would be shorted together,
depending on the settings of the inactive switch.
That would be quite a bunch of diodes, thats what always held me back.

Cheers,
 René


--
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159