[sdiy] Re: [AH] totally insane!! system 700 sequencer

[ASSI]

On Freitag 11 Juli 2008, harrybissell at wowway.com wrote:
> I'd suggest that you use a suitable color LED, with a capacitor
> across the LED. The current limiting resistor and the cap will
> form a LPF that will make the turn-on slow, the turn-off slow,
> and the LEDS to get dimmer as the sequencer runs faster...

This does not even begin to mimic what a Vactrol does.  For 
starters, total brightness of the filament is related to the 
fourth power of the filament temperature (Stefan-Boltzmann law).  
Then the LDR has a spectral response that needs to be folded with 
the with the temperature dependent spectral density of the 
emission, so you need to go into Planck's radiation law.  The 
resistance and hence energy dissipation of the filament is also 
highly dependent on temperature, which adds another nonlinearity 
that also depends on the characteristics of the drive circuit to 
boot.

The emission from an LED is proportional to drive current to first 
order and it is in a very narrow spectral band so that most of it 
will be captured by the LDR, even with the slight shift of the 
spectral emission peak with current.  No amount of linear 
filtering can change that.


Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk]>+

SD adaptation for Waldorf microQ V2.22R2:
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