Having trouble with a simple build

[fldrvr]

I'm having trouble with this simple optotheremin:

http://www.geocities.com/SoHo/Lofts/8713/optotheremin.html


I'm fairly certain I've got all the connections right- as far as my understanding goes. I used a cap with the # 224 on it, so I'm assuming its .22 uf. Is this too high a capacitance value?

Also, I think that my opto resistor may be too high a value. It came from Radio Shack and there were no values printed on the package, but it is of a fairly large physical size (3 or 4 mm across). Think that's the problem?

I'm finishing up an APC right now. Hopefully I can post some shots of the finished build

Thanks

[andrewF]

The original cct suggests a .01uF (#103) and the article mentions .1 uF cap (#104). maybe 224 is too high.

Your optoresistor is quite small! I would guess the smaller it is the less sensitivity you can obtain.

test it in very bright light for best chance of success

[fldrvr]

Thanks.

I was comparing the optoresistor to the others that came in the package; some were only about 1-2mm across. Am I right to assume that smaller=less resistance?

224 happened to be the closest value to .1uf I had at hand. Oh well, mabe I shoudl lower the capacitance by soldering another in series.

Any other thoughts, electro-musicians?

[Coriolis]

Hi,

I've actually built this circuit once, and it works with the given values.

Seems that the combination of your photocell and the wrong cap is doing this.
Or maybe you have the pinout wrong on the transistors you are using? Sure they work? Bad solder joints? Even with something as simple as this, a lot of things can go wrong (he said from bitter experience ).
Photocells of 3-4mm diameter are fairly small - I have some that are 10mm.
However, it's difficult to know if size affects on and off resistance - these things hardly ever have the mark of a specific maker, and so a datasheet is almost impossible to come by. Trial and error is the key here...

C

[fldrvr]

Yeah, my first attempt I used different transistors than those specified... that didn't seem to work so I did use those from the schem- so now the only difference is that my cap is a bit bigger-

Well, I'll have to go over it again. Maybe I have a cold joint or something.
At least someone else has built it here so I know it should work as shown.

[fldrvr]

I got it to work finally... I had to undo all the connections and redo solder everything. I had made a really dumb mistake (which I won't say; but it was real noobish). Luckily the rebuild went smoothly.

Nice little oscillator that works on a single 1.5v battery- 4 components, battery, and a switch- can't beat it for simplicity. Newbies take note- a quick and easy first build. Just remeber to orient your parts in the right direction

thanks

[Coriolis]

Congrats!

Oh man, it's so important to have some succes with those simple builds.
I remember the first thing I tried to solder together years ago, was the simplest possible distortion for guitar - about 1 transistor, a couple diodes, and not much more. of course it didn't work. Tinkered with it a bit, and finally got so discouraged, I didn't touch a soldering iron for a couple of years! If had only kept at it, I would have been 2 years ahead of where I am now...

C

[fldrvr]

Thanks for your support C. As i'm sure you know, it's always the simplest things which confound us the most. It was doubly frustrating in that I had already put together a Lumivox and an APC, both of which are not complicated builds, but certainly more complex than that circuit. Oh well, this will teach me to to double-check everything before I commit a component to the board.

Now I'm wondering about using that same circuit and applying it as the oscillator for something like a WSG.... I have the appropriate ICs, but yet, there is something about going the transistor route that I find appealing.

I don't have a good grasp of the architecture of the schmitt triggers in the 40106, and don't know how to apply the circuit to the WSG- my noobish comprehension does not extend that far. Maybe someday.

I coud probably apply it to soemthing like this:
http://www.getlofi.com/?p=327

Perhaps some on this forum could chime in with thoughts- Yes I Know It Would Be Easier With The IC- but I've got a crapload of transistors sitting aroud.

Thanks again C! Your comment were much appreciated.

[Coriolis]

You're very welcome.

C