Commentaires sur : Piezo transducer signal conditioning

Par : Artem

Artem — Wed, 23 Jun 2010 20:19:11 +0000

This is a very nice article, but i have done some playing with piezos and i have to say it is not that simple. I want to put a piezo in a box and hitting the box will trigger some event. The box is 16mm woods. SO, the voltage spiked from a hit is about 100-200mV only. But you hit it really hard then you’ll get around 10V. I need to detect both types of hits (not distinguish, just detect, they are all the same to me). The problem here is the diode. With only 200mV spike the diode will not let it through. So, i need to amplify it first! A simple NPN transistor might help, do you think? So, when the signal from the piezo will go to the base the output voltage with like 100x more (i’ll take a trans with gain of around 100) but not more than the Vcc. Fo example, 50mV from piezo will result in 5V output (Vcc). However, I, again, don’t know what to do with +10-20V on the base from the piezo? Allowed max Base-emitter voltage is usually around 6V. Put a zenner to the base? Then what will happen to it on negative voltage it? It will conduct and we’ll have a short cicuit. Any ideas?

Par : Philipp

Philipp — Wed, 10 Mar 2010 09:51:03 +0000

Hi Leucos,

thanks for sharing your work!

I have a more general question regarding piezos, as I am currently starting work here and am mch more aware of soft- than of hardware.
So: Is it possible to distingish between pressing an d depressing the piezo? Will that give any different output using your circuit?
In the situation I am using the piezo in, it will be pressed and after a longer time, it will be depressed.

Sadly I do not have an oscilloscaope available so it woud be nice if you could help

Par : leucos

leucos — Sat, 12 Dec 2009 01:21:11 +0000

@gal : the point here is to remove voltage swinging. When you smash a piezo, you have a lot of spikes going up and down.

Having R & C in // will dampend « down voltage spikes ».

Imagine you have a high voltage spike. The cap will charge instantly and Vo will be as high as Vi (Vo and Vi used here are according to the wikipedia schematic).
Now when Vi drops to 0, the cap is still charged and will « slowly » discharge thru R.

All in all, Vo will rise exactly like Vi, but will fall slowly (according to the RC constant).

You can test this at http://www.falstad.com/circuit/

Create a circuit with a R, C, voltage source and a switch and test it out.

Par : Gal

Gal — Fri, 11 Dec 2009 13:36:29 +0000

Hi,

I did scroll down to the wikipedia page …
There they mention the *Parallel* RC circuit that
you are using.

It says : \"The parallel RC circuit is generally of less interest than the series circuit. This is largely because the output voltage Vout is equal to the input voltage Vin — as a result, this circuit does not act as a filter on the input signal unless fed by a current source.\"

Here, in all your scope captures, you talk of voltage, and not current, so I don\’t understand..

Par : tuk

tuk — Sun, 29 Nov 2009 18:21:58 +0000

thank you very much. It has usefully for me.

Par : leucos

leucos — Mon, 02 Nov 2009 08:49:28 +0000

Hey Gal,

Please scroll down on the wikipedia page

Par : Gal

Gal — Sun, 01 Nov 2009 21:24:54 +0000

Hello,

You say this circuit acts as an RC filter, but looking at http://en.wikipedia.org/wiki/Rc_circuit
isn’t the R and C suppose to be connected in Series ?
whereas in your schematic they are connected in parallel ?

Par : leucos

leucos — Sat, 24 Oct 2009 12:27:42 +0000

@Fernando : check out http://drummaster.digitalcave.ca/index.jsp
There are loads of informations there to build an electronic drum.

Par : fernando

fernando — Sat, 24 Oct 2009 01:51:05 +0000

Thanks for the fast answer Leucos.
And by the way, my world is the software and in the last time i have working hard on vst’s and midi software, sequencers, etc., and i’ve hacked a gamepad (wheel) to build a midi floorboard and the sustain pedal for my keyboard, and now i’m programming the arduino to get the piezo signals to finally build the drum and perform a vst like addictive drums. My next project will be to build a breath controller (maybe hacking a broken clarinet). In the music world i play guitar and keyboard, but we (almost a band) need the drum, so with your work we are closer to get it.
I know that i’m still a newbie in the hardware world but maybe i can help in some way to thank you, so any doubt just let me know.
Thanks again.

Par : leucos

leucos — Fri, 23 Oct 2009 20:16:04 +0000

Hey Fernando,

For the BAT85 : Schottky *is* the spec. Schottky diodes are special diode with a low forward voltage drop. So you could ask « a diode with a low Vf », but you’d better ask for a « schottky diode ».
For the Zener : the spec here is the voltage, 5.1 V. The other parameters aren’t that important.
For the capacitor : 4n7 means « 4.7 nano Farads ». So just ask for a « cuatro nano siete » and it should do the trick

glhf,