[sdiy] FSR-controlled CV/LED

[derek]

Hi folks,

I'm experimenting with Force Sensing Resistors for two specific 
purposes right now. One is to control the brightness of a LED. The light 
from this LED will be interrupted by a spinning pattern printed on a 
transparent disk, which creates a tone when it falls on a photodiode. An 
optical organ so to speak:

http://macumbista.net/?page_id=539

The brightness of the LED would affect the loudness of the output 
signal. Obviously, a PWM solution would not work: you would hear the PWM 
frequency in the audio output. So I'm looking for direct, analog 
control.

I am using Ken Stone's LED driver circuit:

http://www.cgs.synth.net/modules/cgsld.html

and playing around with resistor values. I place the FSR in series 
before the 100K input resistor, with +9V being sent through it:

+9V------FSR----100K----base of transistor

The FSR is an FSR-406. I can get the circuit to respond, however the 
slightest pressure lights the LED to full brightness. So my question: 
how can I change the response curve here?

Circuit will be single supply, 9V battery powered, if that makes any 
difference.

I am also looking at using FSRs in place of the capacitive sensors in a 
Serge TKB-like arrangement. And my question would be the same: how do I 
affect the response curve to get more variation from the pressure? 
Again, digital PWM options won't work here... the slew needed to get rid 
of the PWM frequency in the output CV would start to affect the response 
time of the FSR.

I apologize for the fairly basic level of this question, as I'm 
primarily an artist and not an EE.

Thanks for any and all suggestions!
Derek
-- 
derek holzer
noise.art.technology
http://macumbista.net

-- 
derek holzer
noise.art.technology
http://macumbista.net