[sdiy] LM358 datasheet VCO on spilt rails

[Matthew Smith]

Quoth James Patchell at 07/02/12 13:55...
> As I recall (this was 40 years ago...well, 39), I just used a voltage
> divider and a bypass cap.

Good enough for breadboarding :-)

> The control range was 0 volts to about +18 (just a hair less as I
> recall).  If you look at the frequency control part of the circuit, one
> leg is basically a voltage divider that goes to the + input of the
> op-amp.  The common mode input range of the LM358 is 0 to VCC-1.5
> volts.  So, you can run the control voltage up to the point where the +
> input is at that voltage.

Got it. I have a 24V supply here, so will have a go with 12V/24V.

> And yes, it is a very cheap VCO.  At the time I used this circuit
> myself, I had no way to check to see how accurate it was.
>
> http://www.noniandjim.com/Jim/FirstSynth/FirstSynth.html
>
> On this web page, I have a picture of this thing as I built it.

Love the sequencer!

Lots of potential for this VCO, especially when pitch accuracy isn't 
important. Although, with digital (via MIDI) control, counting the 
timing of the square output could make for very simple automatic tuning.

Thanks for your input, Jim.

-- 
Matthew Smith

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