[sdiy] Really Low, LFO

[Oren Leavitt]

Kyle Stephens 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.
> 
> 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, 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?)
> 
> 

Some years ago, I have gotten half-hour cycle times with the CA3080 OTA 
w/CA3140 integrator triangle core. Triangle symmetry looked good, too.
I think I was using 2 or more 10nF (0.01uF) polystyrene caps wired in 
parallel.

It's based on the function generator in the CA3140 datasheet:
http://www.intersil.com/data/fn/fn957.pdf

- Oren