Micro-Theremin IC

media at mail1.nai.net media at mail1.nai.net
Thu Mar 12 04:07:01 CET 1998

>A project called the Micro-theremin calls for a CD4049CMOS hex inverter
>My localparts place -Radio Shack, has a 4049UB hex inverter buffer. Can anyone
>tell me if these are similar, and or can be interchanged?

They are very similar if not the same exact chip -- just check the
tolerances of the Rat Shack part and make sure it can handle the
Micro-Theremin circuit (I want to avoid that whole CMOS power supply
argument :)

It is funny that you are seeing CMOS parts in a theremin.  Funny, because I
am working on a replacement circuit for a Paia Theremax (basically I want
to swap in a new PCB) and thanks to Paul Perry I found this circuit for a
"Digital Theremin" that builds oscillators out of CMOS chips!!

This one uses a 4093 quad NAND gate with Schmitt inputs.  One of the input
pins of each gate is tied HIGH to +15 thereby using it as a NOT gate (as
far as I know a NOT gate is another name for an inverter).  There is a 15K
resistor going from output to input -- my guess is that is employing the
hysteresis to create an oscillator.  Perhaps the upper and/or lower trigger
points move around when you wave your hands.

More peculiar is that only half of the NAND's on each chip are used.  The
notes say "4093 pins 2,6,14 = +15v,  7,8,9,12,13 = ground."  It makes no
mention of the outputs of the two unused NAND's (pins 10, 11).  I can only
assume they are also tied to ground -- from everything I heard CMOS
circuits shouldn't have unused pins.

I'll post more on my theremin research as it develops.  I know I'm in over
my head when I'm using the word "hysteresis" in a sentence :)  First, I
just wanted to build filters.  Then I get distracted by waveshapers, fixing
a theremax, and now power supplies!!

Where did you find this Micro-theremin circuit??  I'd like to take a look
at it.


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