The Pulsinator

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Found Objects - A Manifesto

This blog contains alaetoric music.
Most of it is produced by electronic devices with no effective control over large elements of what results.
The timbre of all instruments is very unpredictable.
Polyrhythms emerge from modulations I don't understand.

The Library

Apcdrone
 
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Seq001
 

Low Frequency Oscillation

A report from Locust Abortion Technical Laboratory.

As we all know an RC circuit oscillates.
But it's not much good for making noises and controlling stuff.
Using the RC circuit and a 555 chip gets you a credible audio /sub-audio oscillator.

Web search results get loads of suggestions some which I don't understand.
The classic timer circuit seems to look like this.
But I liked things about this design too.

So I built one with the values in the tutorial Exercise 1 aiming at around 30Hz for a start.

Not what I'd call a square wave but close (ish).
Peak to Peak is 0.040 s according to Audacity which is 25Hz

There's a discussion here with some suggestions about unused pins being dealt with.
Pin 5 is the Control Voltage (Cv or Vc confusingly - CV from now on).
As it's not used I've grounded it through a 10nF ceramic capacitor "may eliminate false triggering"
I haven't seen any yet but why the hell not.
The waveform and period is unchanged,
All the other pins are connected.

Time for some empiricism
What effect does the capacitor have?
The time constant expression for an RC circuit has t proportional to C
Big C big t
10muF increased to 47muF
Produced a stupid waveform!

P2P .190s or 5Hz, these physicists aren't wrong
47muF 10V changed to 47muF 300V
And made no significant difference to waveform - still stupid.
47muF to 1muF

P2P .003s or 333Hz but look at the shape!
back to RC theory
If you big t use big R.
Trials suggested these values.
C=0.1muF R2=220k

Still a bit stupid but it's my stupid.
P2P 0.028s or 37Hz - I'm happy with this as top of range.
Big R Big t
Big t Little f
(from f=1/t)
So a potentiometer in series with R2 sounds a good idea
Leaving R2 in there stops me short circuiting the 555 when the pot goes to 0ohm.
Tried a 470kohm pot I get 11-37Hz - not big enough and no bigger pots
Waveform at 470+220kohm

Stupider (but it could be the axes or the operator variance
Mess with C
.22muF

Forgive the lack of scale (+ units - I've no idea what they are BTW)
P2P 0.190 or 5 Hz Getting very stupid
I need cycles per minute (or 60 times better) and a decent waveform.
Back to 0.1muF and an enormous R2 (? )
Dicked about
Ended up w/ 1.2Mohm and 100nF ceramic cap as C (sounds like 0.1muF to me)
Stupidest yet

Stupid rendering by Blogger too.
Time for a review.

The Review

The 555 is not re-nowned for its low frequency accuracy.

But the Institute is resource starved - especially time.

So that's all folks good enough LFO.

Wait!

More dicking about; sorry empirical research gaves me these values and I'm happy.

R2=1.2Kohm

C=2.2muF

R1=1Kohm

Hi 'n' Lo ranges
Hi = 4Hz
Lo= 1.2Hz - I think the wave form is so stupid I can't measure it (What is going on?)
It's repeating every other peak.
I got near 1Hz by ear.

Notes on stupidity of waveforms

This is meant to be alaetoric - music by accident/chance.

So this is the LFO I've made with the resources available.

It's the LFO of choice because of that.

Stupid = sublime.

What happens when Output from this Oscillator becomes CV for next one?

Modulation

A VCO suggested itself above.

Same design different values.
Was the plan.
Reality - Nowt worked!
Frustration
Composition as relief.
It Worked!

Back to the beginning
Exercise 1 values for LFO
10muF
R1=1k
R2=2k (2.2 in my case but whatever)
+470K pot for range in series w/ R2
Result passable square wave about 25Hz (0.040s)
But at lower f much stupider
Bottom end I cant measure it but 0.3Hz is a guess

Top end, 25Hz

2nd oscillator = VCO
2.2muF
R1=1K
R2=2.4K

(oops getting them Ks muddled)
Much better square wave and predictable f
0.008s=125Hz
Output from pin 3 LFO to CV pin 5 VCO
Modulation!

It's wobbling the VCO 'tween pitches and I can vary the rate.