[sdiy] CD4067 MUX, supplier differences?

Tom Arnold xyzzy at sysabend.org
Wed Oct 17 06:15:55 CEST 2012


On Wed, Oct 17, 2012 at 05:58:25AM +0200, Ove Ridé wrote:
> Do you have/can you make a schematic for the circuit you're building?
> How is the circuit built? Etched PCB or prototype board of some kind?

Two people have replied asking the same thing. :-)

I'm building a PolyDAC.  

All the details are here: 
http://www.vacoloco.net/synths/polydac/downloads.shtml

I had the boards made several years ago. 

I've made a little 4 bit DAC so I could throw the select lines on my scope
while debugging things.

http://www.sdiy.org/xyzzy/temp/polyd/Select%20Lines%20and%20Input.jpg

Lower trace are the select lines.
Upper trace is pin 1 ( the input ) to the 4067.  The first 4 steps you see
are 4 notes I've banged in using a midi keyboard.   The flat line after is
velocity.  I've confirmed I can feed data to those at will.  

They line up nicely with the select lines with data available slightly
before select changes.

http://www.sdiy.org/xyzzy/temp/polyd/Inhibit%20Line%20and%20Input.jpg

Thats the same lower trace, upper trace is the inhibit pin ( 15 ).

If I look at pins 6..9 which are the note lines, pin 9 ( note0 ) has a very
noisy waveform which varies with different notes.  pin 8 and 7 are dead.
pin 6 has a single pulse on it which doesn't seem to vary with anything.

Things I've tried :
Lifted pin 6..9 and looked at output.  More mutilated but otherwise
unchanged.
Lifted pin 15 and looked at outputs.  With 15 free air or to +V, all outputs
dead as expected.  With 15 grounded, same as normal.

Sorry for the fuzzy photos, cameraphone one handed while keeping a scope
probe on pin isn't as easy as one would think...

Any insight greatly appreciated.  I'm fairly certain at this point the cpu
is properly programmed.  It seems to behave as I'd expect.

-- 
 -----------------------------------------------------------------
 - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
 - SynthGeek        -  "...is it a virus, a drug, or a religion?"
 - K6AET            -  Juanita Shrugs. "What's the difference? 
 --------------------         -- Neal Stephenson,  Snow Crash



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