[sdiy] Question about tri-state buffers and encoders

David G Dixon dixon at mail.ubc.ca
Mon Sep 11 00:16:39 CEST 2023

Thanks for the responses.
Brian, I actually left the three highest-priority inputs unconnected.  I
only needed 0 through 12 for my circuit, so I left 13, 14 and 15
unconnected.  As I said, grounding them fixed the circuit, and it works
perfectly now, even though many of the buffer output busses are hi-Z during
Also, I needed tri-state buffers because many of the encoder inputs are
connected to multiple buffers.
There is no schematic, but basically it is Scale Logic for a quantizer.  The
quantizer circuit sends a binary number to a decoder (CD4514) which
generates an integer.  This integer gets sent to buffers.  The buffers are
hard wired to convert chromatic notes to diatonic notes.  For example, for
the Major scale, there are buffers connecting 1 to 2, 2 to 4, 3 to 5, 4 to
7, 5 to 9, and 6 to 11.  (Note: 0 is hardwired to 0, as the tonic note is
always 0, so no logic is required there).  Hence, when the Major scale is
selected, only the 2, 4, 5, 7, 9 and 11 busses will be active (as well as
the 0 input, which comes directly from the 4514).  The 1, 3, 6, 8, 10 and 12
busses will all be hi-Z.  These busses are hardwired to the encoder circuit,
which converts them back to binary and sends them to a DAC.
As I mentioned, the circuit now works perfectly with only the 13, 14 and 15
inputs grounded, but I have redesigned one of the PCBs to add 10k pulldown
resistors to all 12 busses.  Hence, when (if) I build this module again, I
will do it right.
I'm going to make a brief YouTube video demonstrating this module, probably
later today, so look out for that if you are interested.  It will be called
Sketchy Labs New Folding Quantizer Part 2 (Part 1 was about the prototype I
built for the other guy, that miraculously worked even with those three 4532
inputs disconnected).
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