Simple Mint Tin Theremin

Posted: 8/18/2005 9:53:39 AM
aestuo

Joined: 8/18/2005

I recently saw someone selling an optical theremin housed in a mint tin on ebay. Here's a picture:
http://www.authorsguild.net/images/cache/jlennon-340-Inside_close.jpg

This gave me the idea of building a simple digital RF theremin inside a mint tin, then using the tin itself as the antenna. I've heard here that these simple theremins work well with flat-plate style antennas, but will putting the circuit inside the "antenna" create any interference or grounding problems I should know about? I'm new to electronics and I'm thinking of using one of these schematics:
http://www.theremin.info/info-129-1987_Very_simple_digital_theremin.html

http://www.theremin.info/info-128-199_Simple_Theremin.html


Thanks for any help.

Posted: 8/18/2005 2:25:31 PM
Jason

From: Sammamish, Washington

Joined: 2/13/2005

The Apogee kit theremin might be decent for this. I question though how successful you'll be when the entire circuit is surrounded by the pitch antenna. At $30 though, it's probably affordable enough for experiments :)

Link: Apogee Kit Theremin (http://www.thereminworld.com/theremins.asp?m=22&t=27)
Posted: 8/18/2005 4:53:15 PM
Tallwes

From: Portland, OR, USA, Terra, Sol, Milkyway

Joined: 3/1/2005

From what I understand about theremins, I'll be concerned about the circuit having access to ground or the other plate of the variable capacitor that theremins use to control their pitch. From what I know, please feel free to correct me if I'm wrong, theremins use a very large variable capacitor to control their pitch. This variable capacitor consists of the pitch antenna(one plate of the capacitor), earth ground or another piece of metal(for the other plate of the capacitor) and you(the movable part that makes the capacitor variable).

In the case of the mint tin theremin. You would either have to provide a connection to earth ground by plugging it into a grounded outlet or if you want to run it off of a battery, as in the example of the photo theremin you are referring to, you would either have to some how electrically isolate the lid and the bottom of the case and use one half the case as a ground or simply attach an antenna(mount it so its electrically isolated from the case) and use the whole case as a ground.
Posted: 8/18/2005 5:28:31 PM
aestuo

Joined: 8/18/2005

Thanks, if I get a circuit built I'll try isolating the top from the bottom of the tin and using the bottom as the ground. It looks doubtful, though.

I know the "simple theremin" design has been discussed before:
http://www.theremin.info/info-128-199_Simple_Theremin.html

But I have an additional question: how is the battery connected in that schematic? It says pin 14 should be connected to +9v on all the ICs, does that mean I split a wire from the positive side of a 9 volt battery three ways? Why then is pin 1 connected to a + symbol on two of the ICs? Is the negative side of the battery just connected to the ground?
Posted: 8/19/2005 2:16:45 AM
Tallwes

From: Portland, OR, USA, Terra, Sol, Milkyway

Joined: 3/1/2005

For hooking pin 14 of all the ICs to +9v this is usualy done with a trace on the circuit board. Yes, you do hook ground up to the negative terminal of your battery in a portable device including the lower half of your mint tin which you are wanting to ground.
Posted: 8/19/2005 1:20:08 PM
Jason

From: Sammamish, Washington

Joined: 2/13/2005

Wouldn't the battery itself serve as enough of a ground? Try hooking up all the dark black lines on that circuit to the negative terminal, and pin 14 and the two + pins (#1) on the 2 ICs to the positive terminal. If you insulate the circuit from the inside of the tin, then you might just be able to use the tin as the pitch antenna.

This has all the makings of a clever practical joke device :)

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