Theremin

This is the Theremin that I made. It's version one and only cost under 10 to make.

This is the side view. As you can see that there is a volume control which is not really true to the theremin way. As the volume should also be controlled by an aerial. I built an amplifier in it and the shinny thing in the picture is the 3.5mm out put jack

Top view so you can see the output speaker

The nice brass plate is the aerial

There are several problems with the Theremin I have made. The fist being that the speaker and the on/off switch seem to react with the aerial. This is making the device make a constant noise. When I placed the item spread out flat on the my work bench then the device only makes a noise when a hand is near the aerial. I also forgot to fix the battery down, so it rattles a bit.

I'm about to embark on making version 2 using sinewave generators rather than squarewave ones. This will then give it a purer sound I hope. I'm still learning.

However you can make your own.


How to build a Theremin


This instruction set is from my own experiences and may be of some help when making your first Theremin. I have used a circuit by Arthur Harrison who I give credit for as he owns the copy write. I’m going to take you through the basic bits of this project and then tell you how to make it better. Keep this in mind as you may want to read this through first and then do all in one go. I’m not going to tell you how to solder or to shape components or even tell you where to place the components.

First pick you circuit diagram.


For the one that I built I used the following diagram from www.Maxiespages.com called the Minimum Theremin. I don't think that site is there any more .

Another great diagram circuit is the Popular Electronics Aug. 96 One Chip Theremin. The only reason for not using this design was toilet-tank floats are now in plastic and to find a metal one is difficult. If you do know where to find one then this circuit is the one that I really wanted to make. I have found a source of metal toilet-tank floats in the UK but just a little too late. They are also good for making Van de Graff generators with.

Finding components

Now you have decided which diagram to use you will require components. All the components are available from your local electrical wholesaler. You may find that your local TV repair guy or repair shop can order these in at cost. You can also order these parts over the next with companies such as www.farnell.com (click on your countries banner) or www.rswww.com as they will accept credit card for internet orders. You should also shop around as some places have cheaper parts than others. Don’t worry if you cannot find a part as an alternative is always available.

To start with you will need some standard parts for all fun things you’re going to make after you have made this theremin. They would be:-

Stripboard or a development board (I can fit about three circuits to one piece of board)

Tinned Copper Wire 22AWG (to make links)

Insulated wire for connecting up antenna and jack socket

PP3 battery connector

For the circuit I used the following

C1, C2, C7 and C8 = 10uf 16V Electrolytic

All the rest of the capacitors use ceramic capacitors as they are nice and cheep but remember minimum voltage is about 6 volts.

For the resistors use 0.25W general purpose metal film or carbon film resistor.

The size of your jack socket depends on the size of your jack plug. A 0.25in one is standard on most PA systems.

For the antenna you can use copper plate to the dimensions in the diagram about 2mm thick. So that you don’t effect the antenna us plastic nuts and bolts to fix to the out side of the case.

Your case should be the thing that is very important. This will effect the way that you theremin looks. Plastic is a good recommendation as it takes little work to fit electronics in.

Making the Thing

This is up to you how you make the electronics as every one has different way of designing on stripboard. There are several things to take into consideration since this circuit can be prone to noise. Listed are a few guides to help this.

a) Split the circuit into 4 parts

N.B When placing the parts on the strip board it is best to keep the circuit in the green area away from that in the red area as they can have cross talk.

b) Put decoupling capacitors on the power pins of the IC components. (use a 0.1uF ceramic will do the job)

c) Remove all unused copper tracks from the board.

d) Use small length of wires when connecting jack socket and antenna

 

 

Other things to make you theremin a bit better

1) Amplifier
You can add an audio amplifier on the output of the theremin to so that you can connect a speaker and all so have some volume control. There are two places where this can be inserted. One is before the jack socket and the other is after. It does depend on if you want to vary the output of the jack socket.

I used a LM701 made by National Semiconductors. But a standard 741 could be used. Any basic audio amplifier circuit of the net could be used.

2) Switch
I know it goes with out saying but you should put a switch on the outside of the case. If you use a metal on try and place it out of the way from the antenna. (I didn’t and it means that my theremin will never go quiet unless I turn down the volume)

3) Speaker
You can connect a speaker so that when a jack plug is not inserted a speaker inside the case will be connected. This is simple to do and you can use a speaker from an old PC case.

Other things like testing
When testing, do not fit it into the box first. It is easier to test and tune the board when it is flat out on the bench. Keep the antenna away from the circuit. Once working, place in case and test again doing any fine tuning that is needed.

Thing that I forgot to tell you
Have fun and if it isn’t as good as you hoped then try again and play with components and placing etc on the board.


A great place to get all thing theremin is