LED brightness based on vibration sensor

[InTheCrag]

Hi,

I know the basic way the circuit should work, but I'm not very familiar with all the components out there. (So many!)

Basically, I'm trying to have an LED turn on whenever a vibration sensor (piezoelectric film) produces a voltage, however I don't just want it to be a simple on/off function. I want the LED's brightness to depend on how hard the sensor is struck, or rather, depending on the voltage output of the sensor. Obviously the sensor can't drive the LED itself, so I was thinking I need an OP amp of some sort, but I can't seem to find the right one for the job. Does a transconductance amplifier sound right? The only ones of those I could find didn't seem to support enough current that I need... I'm planning on using a high brightness LED that could draw anywhere from 200-500mA. Besides that, I'm not sure what I could possibly use.

 

[things]

piezo speakers produce a tiny output voltage when they are squeezed, enough to power a 3mm diffused green led dimly, so you could probably just hook it up to a transistor and when the piezo is struck, it will set off the transistor allowing more current for the led. the piezo will output different voltages depending on how hard it is hit or where it is hit, thus changing the amount of current the transistor will allow to flow? (i think)

 

[InTheCrag]

That's actually what I was thinking at first, but for some reason I was convinced it wouldn't work properly.

edit: Yeah, I'm leaning towards an FET now. If I understand this correctly, I can use one in "linear mode" to act as a variable resistor, right?

 

[things]

are you just using one led? if i remember right, the more amount of current you put into a transistor, the more current the transistor would let through.

 

[InTheCrag]

Technically it's the more voltage you put in a transistor, but yeah.

I'm pretty confident on using an FET now, but now I can't seem to find one with a gate that has a maximum voltage high enough, as the sensor can produce over 70V in certain situations... Grr...

 

[things]

i didn't know that it would output that much power?? what is this going to be for???