Can anyone help me improve my design?

Posted: 7/11/2012 2:54:07 PM

Joined: 7/11/2012


Just breadboarded a VERY simple Theremin using a 4093. Pretty happy with it but jus wondering the best way to increase the effective operating pitch distance beyond a couple of inches.........thanks in advance!


Posted: 7/11/2012 3:52:28 PM

From: Northern NJ, USA

Joined: 2/17/2012


Stick one or more linearizing inductors in series with the antenna (check their self resonance point to make sure they will function in this mode).  Use 3/8" tubing to make real antennas. 

I'd suggest you avoid Schmitt trigger devices.  Use buffered 4000B series inverters (NOR or NAND with the other input tied hi/lo as necessary, for some reason a decent buffered hex inverter does not exist).  Make the oscillators LC.  Do something for static protection like a neon bulb and/or littelfuse SP721.  Regulate the supply voltage(s) with inexpensive three terminal regulator(s). 

That may sound like a lot, but it really doesn't take much to move a design out of the squeaker toy category.

Posted: 7/11/2012 6:41:57 PM

From: Colmar, France

Joined: 12/31/2007

As long as there are (most probably) RC-oscillators around the 4093, additional coils will not help at all. Only a longer and/or thicker antenna.

Posted: 7/11/2012 6:46:58 PM

Joined: 7/11/2012

Thanks for the replys guys! I'll plough through all of your tips!!!

Posted: 7/11/2012 6:47:54 PM

Joined: 7/11/2012

It is a RC-oscillator by the way

Posted: 7/11/2012 7:33:38 PM

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

Several things to note: ( I am presuming you are using the 4093 hysteresis - resistor [R1] from output to input, input to antenna / capacitor to ground)

1.) The hysteresis 'window' on the 4093 is quite small, which gives a low level triangle waveform on the antenna.. put a resistive divider on the input to increase the antenna voltage.

2.) Put a resistor and capacitor in series and connect this across the resistor R1

Make the resistive divider have 47k to antenna and 100k to ground - if circuit fails to operate make the 100k larger until it does oscillate. Make the TC of the series R + C about 1/4 of the period of the oscillator, and make R = 1/2 the value of R1.

The above mods will improve performance (range and linearity) a bit - but not much. Increasing the length of the antenna (as Thierry suggested) is, IMO, better than increasing its thickness - A long antenna will "see" your arm (at an angle) and the geometry helps to improve linearity.. (This is one of my quirky ideas - I believe that antenna geometry greatly affects performance of non-compensated "antennas") and think I have proved this in practice.. RC oscillators usually make unplayable theremins, but with a really long thin antenna (1.2m - or twice the arm length) one can actually play a couple of octaves quite easily) - Even better - (but more difficult, and it looks silly) is to angle the antenna towards the player.. 45 degrees gives great linearity!



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