[sdiy] Re: Vactrols and contact mics

[cheater cheater]

I think he just wants to put it in a vactrol, in which case it would
make more sense to me to make a chopper and filter it.

D.

On Fri, Oct 16, 2009 at 2:28 PM, Antti Huovilainen <ajhuovil at cc.hut.fi> wrote:
> 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
>