[sdiy] Really Low, LFO

[cheater cheater]

Leakage current of your capacitor and off-resistance of the transistor
used for resetting the core are going to be the issues, I think.

If you want an infrasonic LFO I suggest doing it in DSP, there's no
advantage to using analog at those frequencies that I can think of.


On Fri, Apr 2, 2010 at 22:51, Kyle Stephens <lightburnx at yahoo.com> wrote:
> Can anyone point me to some reading material on infrasonic oscillator design? I want to build a really low, low LFO, with a period of around half an hour (yes, _that_ slow!).
>
> As HF designs have their share of issues that get worse in that spectrum, infrasonic has its problems too I would imagine - I just don't know what exactly they might be.
>
> For my app, accuracy isn't as important as precision/repeatability, though if both are possible then both are welcome.
>
> Closest I've found so far is this:
>
> http://tinyurl.com/yf9wzp3
>
> I reckon I can tailor it if I make the integrator cap several decades larger, to shift that 0.1Hz to 100KHz range several decimal places downward.

Eh, not really about the size of the cap, it's more about being able
to control the current accurately enough.

> I've a copy of AD's Nonlinear Circuits Handbook, which has some material on the topic, though nothing too specific on freqs beneath 1 Hz (half an hour is ~ 0.0001 Hz).
>
> I spoke to Prof. Lanterman about this a while back, and he recommended a microcontroller based solution,

Yep, I second that. DSP options (and for an lfo you don't even need a
dedicated dsp uC such as a 56k) give you accuracy AND repeatability;
but they're easy  to badly implement on their own (aliasing, ...)
although, comparing the typical sampling frequency you'd run this at
to the frequency you expect, the error in pitch coming from aliasing
on the discontinuity (which gives you only an error of +-1 sample,
maybe 2) will be minuscule. Your biggest problem will be implementing
an accumulator register big enough, I think.

D.

> and while that's something I want to break into, it's a whole 'nother can of worms too. If this can be done in analog, it'd be a cool achievement and an enrichment exercise if nothing else... :]
>
>
>
> _Kyle (so slow it Herz?)
>
>
>
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