Analog Theremin Sensor Construction Problem/Question

hi there, I want to to build a proximity antenna sensor circuit that outputs voltage.

I will conect this sensor to the arduino board ( www.arduino.cc ) that can read this information and send to the computer, where I can then do wahtever I want with the information (just like a MIDI).

I found such a schemata at: http://asmir.theremin.ru/tsensors_design.htm

you can find it at Analog Theremin Sensor#3!

It says it works by the same heterodyning principle, and the diagram should be self explanatory to anyone involved with electronics and theremins (hopefully everyone who gets to read this.

But the thing is that I dont know anything about electronics or theremin principles... and it seems that the components labled as L1 are not clear, because I couldn't et a clear answer on what they are from everybody I know who has deep knowledge on electronics.

People, please, what are they?

it says they are stable coils around 200uh

but the symbol is for a transformer...

thanks a lot, alex

He uses the primary or secondary coil of a transformer as a self, it's a convenient method if you don't find the right self..

About how this ciruit works, it's quite simple: the theremin part outputs a wave which frequency depends on the player's hand position (nothing new there).
It passes through a band-pass filter, and the most difficult part there is to set up the right center frequency, the right Q (bandwidth) to get a approximatively linear and proportionnal relation beetween the frequency and the output level. To get this linearity, you gotta set the filter curve to be close to a straight line in the frequency range of the theremin.

When you got an output that linearily depends on frequency (and then player's hand position), the wave is rectified as in a power section, to get a continuous voltage. Because the value of this voltage is a function of the input amplitude, you got a link beetween the output continuous voltage and player's hand position.

This is a bit of theory, you can make it with several modules: Theremin -> BP Filter (with variable center frequency and Q) -> Rectifier section.

Good luck =)


PS: If this system is correctly set up, you can use the theremin sensor as a CV device...

thank you franky.., now tell me something, what do you mean by a "self"?

cheers
alex

hum sorry i picked up the french word.. A self is a coil, a basic inductor.. You can use the primary of a transformer (or the secondary) as an inductor.