Began building a theremin, need help completing

Posted: 2/5/2014 10:23:18 PM

Joined: 2/5/2014

Hello all,

I've been constucting my theremin for about 6 months now. It's not for musical purposes but for a science fair. I've gone through various problems. I began with the cmos 4093s and 4077 simple circuit. My CMOSs burned out and i switched to ttl. Then i struggled with decoupling and various other problems. Now i have two oscillators (NAND). One is variable and the other is fixed. They are oscillating at about 430 kHZ. Here is my schematic


I'm using 74ls132n and 74ls266n. I'm using the 266n as a mixer (XNOR). 

I detected two signals on my AM radio. My problem is that this thing isn't varying to hand capacitance. If i put a wet finger on the capacitor, i can detect a change. But bringing my finger closer and farther yields no change.

I need it extremely sensitive because i'm trying to detect heart beats with this. Please help me, i will really appreciate any help to making this detect chest movements. 

Posted: 2/8/2014 1:41:31 AM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

Hello eswara,

I cannot see your schematic, you need to edit your posting and correct the link.

4000 series or other CMOS is far better suited to theremins than the 74ls family - the threshold voltages and impedences of TTL just aint ideal - But for a science fair all you need is a TS556C dual timer and a simple diode mixer.. or one of the many simple schematics.

You say you "blew up" your CMOS - did you ever determine how? Simetimes its best to at least learn from your mistakes and correct these rather than heading off in a new direction.

Anyway, make the schematic viewable and ill see if I can help (or someone else might) but right now there is nothing constructive anyone can do or say.


your link

does not point to a image file (.jpg or .gif or whatever) - and using the above link takes one to a log-on page for AAC.. Go to the image, get (from its properties) its full URL, and insert an image using this URL.

OK - as an AAC member I logged in and saw your "schematic" .. Its utterly meaningless! Theres no logic, but a few unspecified crudely drawn opams in some meaningless configuration

Cannot help, sorry. can only help those willing to help themselves a bit.. If you cannot take the time to learn simple logic symbols and put more detail down, I certainly cant be bothered to try to debug it!

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