5 replies to this topic

[JBeck]

Hi, I'm looking to use a piezo element as a trigger. As an electronics newbie, I found me a tutorial for Arduino (http://www.sparkfun.com/tutorials/330), but I don't dare connect the element I have, as I understand piezos can generate very high voltages (although at low current). A regular multimeter isn't able to measure the output since it's such a short burst, correct?

 

Should I be able to deduce the range of output from this datasheet? http://www.electroki...e/download/3209  (Impedance: 200 ohm @ 2.8 kHz   Electrostatic Capacity @ 1kHz: 26 nF)

 

And how do I protect my Netduino from frying?

 

Thanks /Jonas

[Mario Vernari]

Hello Jonas.

True that a piezo can generate high voltages (relatively to the limits of the Netduino logic). But...to break you car glass you need enough energy: a child could not get it. The same thing is for frying a Netduino: the piezo may generate a voltage too high, but its energy is very small to destroy the board.

However, you should bear in mind:

• the Sparkfun article shows correctly to place a resistor in parallel: this is needed to suck part of the energy generated by the piezo. Any resistor is made to transform electric energy to thermal energy.
• the voltage generated by the piezo is proportional to the derivative of the pressure, and not to the pressure itself. It means that if you press tightly the piezo with fingers, then probably you won't read anything. Instead, by hitting it, the pressure variation is considerable, as well as the voltage generated.
• That said, hitting the piezo is a very short task in term of pressure/voltage, and the Netduino is relatively slow on it. You should amplifiy/experiment some circuit so that every hit on the piezo yields a logic high, suitable for any boolean input.

I should have a piezo somewhere, and the very best thing to do for inspecting the actual voltage is connecting it to a scope. Let me the weekend for doing that.

 

Now a question to you: what is the purpose of the piezo in your project?

Cheers

[JBeck]

Hi Mario, thanks a lot for the information! As a newbie, I find educating myself in electronics using the web is a lot harder than I thought, I rarely find the explanations on a level suitable for me, so this kind of help is very valuable. (I think I might have to find a hands-on class in basic electronics.)

 

My long-term project for the Netduino is pretty broad - "enchanting" my son's room with sensors, LEDs, audio analysis, perhaps a Kinect sensor later on.The piezos will be used for creating "buttons", velocity sensitive (as in MIDI terminologi) if possible, out of parts of the room.

 

In fact, I've also just bought a MegaDrum kit, which I will use for most piezo sensors. For some things I think it'll be better to read the sensor directly rather than through MIDI - and I hope to gain a better understanding of the mechanisms that way.

 

If reading the Netduino analog port is too slow, would one solution to use a separate ADC with a cache memory that I could poll?

 

Thanks! /Jonas

[Mario Vernari]

I asked you about your goal, just because I imagined something related to "drums".

Please, bear in mind that, about 30 years ago, some friends (always money-less) needed drums for their music passion, and they create a amazing drum from scratch using loudspeakers as sensors, mounted on a rubber-wood frame. They only things they purchased were the holding steel-frame (don't know the name), and the sticks. Loudspeakers were perfect as well as inexpensive as hitting sensors. The circuit was refined over years, but the sound (obviously "electric-like" as in the early '80s) was soooo nice!

 

Okay, for your project I'd suggest an Arduino as sensors front-end: the piezoes can be read with ease using a simple-yet-fast C/C++ routine, then the collected values may be read via serial UART or SPI from the Netduino. Also, depending on what's your final desire, it could be the Arduino doing all the stuffs (I mean just the drum).

 

Hope it helps.

Cheers

[JBeck]

Thanks, that sounds like a simple solution - a lot easier than finding specialized ADC components and trying to get them to work together.

 

Would it also be possible to modify the Netduino firmware for high-frequency reading/buffering of analog input? Far beyond my current skill set, but maybe a future option. (Seems this is discussed in this thread: http://forums.netdui...d-expectations/)

 

I like the use-what's-available approach of your friends. After the global economy collapses and we're in Mad Max world, I hope to be one of those little old men, the Qs of steam punk, in a dark workshop with electro junk, assembling new devices for the hero. Unfortunately I think a rat is required as a pet for that role.

There's still a few years for me to learn electronics, I think

 

Thanks /Jonas

[zee]

Hi..

 

I need help here! I am doing a project for drum with led lights up upon hit the piezo. Can arduino codes be used for netduino plus 2? Researching since just now and the results are all for arduino uno.