NLC Spasm

The SPASM is a LDR controlled jerk chaos module in Eurorack format.

This is a DIY build.

This module takes the classic Sprott jerk circuit and replaces all the resistors with LDRs.....a 7 way vactrol. 

 

This means the brightness of the LED in the giant vactrol controls the frequency of the circuit.

What exactly is a JERK circuit..??

"Jerk equations were developed by JC Sprott, .... (they) are very simple equations that are easily implemented as circuits, the diode is the nonlinear element, which is cheap and easy to get. Many chaos circuits use multipliers like the AD633 ($15 each), so I like to avoid those". (Andrew F).

The intro of this paper is a good explanation - http://sprott.physics.wisc.edu/pubs/paper229.pdf

Op amps first.

RL LED resistor ... using a 0805 resistor for panel LED... I'm using a 10K.
RLBox .. using a 2.2k 

I'm using GL5549 LDRs...I have a bag of 100's of these suckers.
These LDRs can go up to 10M+ (In fact they range anywhere from 10MΩ to 20MΩ), so they will be a lot slower but should give a much wider frequency range and some very unpredictable outputs.

I'm going to use 1uF caps with this so as not to go too slow. The great thing about SMD caps is that they are so easy to change. Andrew F says that 10uF will make this extremely slow, and 100nF very fast

 Building the vactrol box

 Line everything up & then solder
Only using double headers as i didn't have any singles on hand.

Feedback pot. "If building a very slow version, a 1M pot is better but not essential". (AF)
I'm using a A500k pot

There is a single LED in the Vactrol surrounded by 7 LDRs

Get the LED orientation right.

The LED section of the vactrol schemo.
 The anode goes to ground

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More links to NLC (nonlinearcircuits) projects.
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Links:
+NLC Blog 
wiki

bom

+ Sprott's Gateway 
+Wolfram - Demos