Getting useful peak data from a piezo sensor

Forum 2005-2010 (read only) Hardware Interfacing
#1

Hi all, this has been driving me nuts for a while!

Im trying to use a piezo sensor to allow me to get velocity sensitive data coming out my arduino.. I have the piezo connected to analog in, pin 0 and a megaohm resistor across the legs of the piezo between the input and ground.

My first sketch initialised a variable (threshold) and i stated: val = analogRead(piezoOne); if (val >= THRESHOLD) { Serial.print(val, DEC);

and then delayed some time inside that 'if' loop to stop repeated readings. I noticed the numbers i was getting out were seemingly pretty random, though the thresholding worked relatively well. A very hard hit would often register a low val, and consequently a soft hit might have a very high val.

I realise maybe that this is because it is simply throwing out the first value that it samples that is above my threshold. I wanted to find the peak value though, or an indication of relative hit velocity.. Is there a way I could incorporate this well in software on the Arduino?

I looked at a link to todbot: spooky-arduino-projects-4-and-musical-arduino/ which claims to have a hack attempt at measuring velocity of a piezo's hit... but it really didnt work... the t variable did not seem relative to my strike velocity at all!!

Thanks for any advice or comments, all.

#2

complete guess

You should try streaming the entire output, see if you actually are getting those high values. Or, add a few if statements with small delays, like

if(val >= threshold) { delay(1); val = analogRead(piezoOne); delay(1); if(val >= threshold) { Serial.print(val, DEC); } }

That way that first 'bump' won't get printed, but the next reading value will.

#3

Have a look at:-

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1238824988/2#2

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1221041538/3#3

Also consider putting a small capacitor across the transducer to hold the peak, or using a peak detector circuit in front of the A/D.

#4

Thanks for the replies so far. What do you deem to be a 'small' capacitor rating? The piezo's are attached to the underside of a drum skin right now, detecting hits.

#5

It doesn't have to be physically on across the sensor just electrically at the Arduino end. say start with a 0.1uF and see where that gets you.

#6