5219Views12Replies

Author Options:

Simple transistor oscillator required - suggestions? Answered

I'm after a simple transistor-based oscillator for the basis of a 1-octave organ. I want to use recycled bits, which I have a lot of, and I reckon someone knows what's good as opposed to going looking for something. Crude, basic, simple, nothing sophisticated.

L

Discussions

How about this one?  Two transistors (NPN and PNP) but fewer passives.  Come to think of it, I used this exact circuit for an alarm circuit many, many years ago.

Yea, I'm happy enough with that, I may change later but it works and it's easy to fiddle with.

L

That looks about right, I'll make one some day soon and test it - let you know.

L

Another traditional approach: websearch "top octave chip".

Some circuits from:
Graf, Rudolf F.  Encyclopedia of Electronic Circuits Volume 1. Tab Books. 1985

The attached pics are  from the chapter titled, "Audio Oscillators"

I'm guessing that the specs for the transistors aren't critical, i.e. the diagram says SK3124, but probably any NPN transistor will work. 

eec-p67.jpgeec-p69.jpg

Astable multivibrator with 8 (12 with semitones) switched resistors to replace R2?  You'd need a 'scope / frequency counter to set it up and it would drift with temperature but crude, basic and simple it is. (Trying to resist the urge to up the crudity level by mentioning err. .  equine entertainment devices . . . and failing #;¬)

Yes I thought about those, but I was hoping something with fewer component would be suggested. If no one does, you get best answer by default.

L

OK, relaxation oscillator then.  Rt would be the one to change, although it uses a unijunction rather than a standard bipolar transistor and I think the ratio of R and C is more critical for it to oscillate.
If you've got a CMOS logic inverter lying around you can make an oscillator (or 6) with just a C in the input and R as feedback.
I thought of a modified joule thief circuit, but their frequency is almost entirely dependent on the inductor.

 

Yes I thought of the last, but I didn't know about the frequency ranges for these things.

L