Building a Theremin: Choosing the Right Chips and Understanding Circuit Diagrams

[k_squared]

I would like to construct this thing:
http://www.thereminworld.com/pics/schematics/simple.jpg

However, I am unsure of the chips to use:
*Can I assume the 4093 is going to be a nand quad gate?
(say: http://www.thereminworld.com/pics/schematics/simple.jpg)
For the 4077, what about this?
http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=568-1701-5-ND

Also, I don't quite follow how I'm supposed to hook that up, is the diagram a reference to a 'logic' that I should be following? I uh, don't understand that at all, although I suppose I MIGHT be able to figure out what exactly the chips do.

Oh, and uh, thanks again for all that help I've been getting.

 

[vk6kro]

That circuit has two Schmidt trigger oscillators.
These are the two 4093 gates. Normal NAND gates won't work in this circuit.

They oscillate above human hearing frequencies.

They are mixed in the 4077 chip to give a difference frequency in the human hearing range.
This is an exclusive OR gate.

To construct it, you just need to buy the chips and wire it up. The pin numbers are given on the diagram. Not shown, but necessary, is that the chips must have pin 7 grounded and a positive supply voltage on pin 14.
Ask for the CD4093 and the CD4077.

The "antenna" connection shown would probably go to some flat plates that you move your hands near to change the capacitance across the 100 pF capacitors.

They have made some attempt at making it sound better by using some filtering on the output. That is why the 10 K and 1 nF are there. The output of the 4077 is basically a square wave, so some filtering is necessary.

You might find the tuning of the pot a bit delicate. You would tune the pot until you hear something in the output.

 

[k_squared]

Now that I FINALLY have managed to get on this I was wondering...

Do you say normal NAND gates won't work to becuase the 4093's oscillate at a high frequency, or do I need 'non-standard' 4093's? I noticed I had some faulty links, will this work?

http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=CD4093BCN-ND&x=0&y=0

and i accidently bought a 14077 chip... that won't work, will it?

Well, digi-key will ship at post-only - and thanks.

 

[vk6kro]

The important part is "Schmidt trigger"

The 4093 will work in that circuit but normal NAND gates that are not Schmidt trigger ones will not work.

They work differently and this oscillator depends on that difference to work.

Motorola 4077s have a 1 in front of the number so MC14077 is the same as a 4077 from anyone else. If yours is a Motorola one, you are probably in luck.

 

[k_squared]

I knew I should've posted that chip that I did have:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-14077-5-ND

uh, that one wouldn't make do, would it?

 

[vk6kro]

No, sorry, wrong chip. :(

The one in your circuit was an exclusive-or gate, so you would have to use one of those.

 

[k_squared]

ha ha FINALLLY! Would this
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-9406-5-ND
one do it?

(And if I'm still wrong, could you be generous enough to link to one, somewhere, that would?)

 

[vk6kro]

You need one CD4093 and one CD4077.

The 4093 has FOUR Schmitt Trigger NAND gates in it and you only need TWO, so one chip is enough.

The circuit shows the same pin numbers for the 4093 gates so maybe he used two chips and just one gate out of each. The chips are pretty cheap and this may be worth doing. Read the article and see if he mentions why he did this.

These chips are very commonly available so you should be able to just buy them over the counter at any good electronics store.