Micro-Theremin IC

[Rene Schmitz]

At 22:07 11.03.1998 -0500, you wrote:
>>A project called the Micro-theremin calls for a CD4049CMOS hex inverter
>>package.
>>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 :)

I agree, they are the (almost) same thing. And can surely be interchanged.

>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.

4093 are schmitt trigger nands so they have built in hysteresis, the
resistor forms 
just the feedback for the oscillation. This is the cheapest method for a
square wave
oscillator that I know.
A theremin using a CMOS 556 dual timer and ex(n)or gates for the mixer
appeared in the 
german elektor about last year or so. If anyone is interessted I could scan it.

Hope you find this interessting.

Rene

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