[sdiy] Suggestions for oscillator coarse control methods?

[Quincas Moreira]

personally i like linear pots over the entire range for playability. I don’t mind being careful not to bump into it, and I find octave switches constrictive.

Sent from my iPhone

> On Jan 22, 2020, at 08:03, Spiros Makris <spirosmakris92 at gmail.com> wrote:
> 
> Hello,
> I am looking for ideas on how to implement a coarse tune control on an oscillator. I am trying to get the most stable performance, based on my understanding of the topology (let's see how well I do), so the control method has to be drift resistant or, at least, not be susceptible to it. PCB surface is important, monetary cost less so (let's keep it under 5 euros for single quantities?). SMD when possible is preferred.
> 
> Here is what I have thought of so far, and the pros/cons I can come up with.
> 1. Linear potentiometer. It can sweep continuously, which is good, but because of that is less precise. Cannot do octave switching, for ease of use or playability. Easy to nudge and detune. Cheap. Temperature coefficient of potentiometers is not always quoted. Can replace with a small potentiometer for nudge-proofing but at the cost of playability.
> 2. Rotary switch. Octave switching at specific steps. Up to 5-6 steps commonly available, tactile feel, hard to nudge, expensive, moderate to large surface cost, can be made very precise with suitable resistors.
> 3. Toggle switch. Up to 3 steps, easier to find and cheaper than rotary, the rest is the same.
> 4. A digital hardware switch system, where pressing two pushbuttons in conjunction with a timer and suitably chosen resistors and opamp, LED indication. Looks impressive, can be very precise, high usability, jellybean components, high part count, moderate cost, large surface area, large panel area.
> 5. A bare metal uC with a rotary encoder or buttons, LED feedback, same DAC as (4). Same advantages as (4) apply. moderate cost, low-moderate surface cost, noise considerations, might require additional 5V regulator, has to be programmed in-circuit.
> 
> My intent is to use one of the above in conjunction with a fine pot, with +/- 6 semitones (or 12, it's debatable).
> 
> So what do you like as far as coarse/octave controls go?  What else could I use?
> 
> Spiros
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