[sdiy] Re: Vactrols and contact mics

[Antti Huovilainen]

On Fri, 16 Oct 2009, cheater cheater wrote:

> One way you might control a led's brightness from an analogue source
> is if you copied the general idea of how DSD sampling works - just get
> a very fast triangle oscillator, and compare it to the (normalized)
> signal from the piezo. The piezo signal must have the same p-p
> voltage. Then output a 1 if it's above the triangle wave, and 0 if
> it's below. Pretty much done.

Simple voltage controlled current source is probably easier. "Pro" version 
uses opamp and a transistor but for something in the ballpark you can get 
by with just two transistors.

Harder problem is making the brightness perceptually linear. IIRC, the 
light source intensity should be squared to give perceptually linear 
scale.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova