Connect Piezo transducer to IC from USB Computer keyboard for sample trigger

Thread Starter

SteveSmith001

Joined Oct 5, 2015
5
Hi. I hope someone can help me with a suggestion for this.

I need to connect a Piezo transducer to the IC from a USB computer keyboard, so that I can use it as an external trigger which can be hit with a drumstick.

I have built a similar system using momentary switches, operated by hand, which works well

However, when I connect the Piezo to the IC and connect this via USB to the computer, then the Piezo is triggered as a buzzer.

I am guessing that this is because the USB buss has a voltage to drive external disk drives and similar appliances

Can anyone therefore suggest what I can do to make the peizo function only as a trigger?

All help gratefully received...
 

Alec_t

Joined Sep 17, 2013
12,248
Welcome to AAC!
My crystal ball has gone cloudy ;). Can you post a schematic of your piezo input arrangement, and a link to the mystery IC?
 

Thread Starter

SteveSmith001

Joined Oct 5, 2015
5
Thank you very much for your response - Crystal Ball polish attached ;)

I have attached two photos - one showing the USB IC (extracted from a computer keyboard) and one showing the piezo and the IC , not connected

I have done this before by simply connecting the two poles of a switch to two connections on the IC

When connected by USB to a laptop, this will generate the equivalent of a keypress on a keyboard. For example - if I connect pins 1 and 6 on the IC, the computer registers the letter 'a'

As background - in case there are other thoughts on how to do this - I would like to be able to place the Piezo underneath a mouse mat, and when the mousemat is hit, it generates a letter...

Please do let me know if any further information would helpIMGP3523.JPG IMGP3522.JPG
 

Thread Starter

SteveSmith001

Joined Oct 5, 2015
5
Piezo's generate very low power , and too low to act as a switch for your purposes , what you would need to do is add a single amplifier stage to increase the power from the piezo device.
Here's a thread which should help solve your problem http://forum.allaboutcircuits.com/threads/piezo-trigger-switch.98418/

Thanks very much for that link, and for taking the time to answer. I have done something similar when using piezos as trigger pads attached to an acoustic drum.

My query here is whether it is possible to prevent the Piezo being triggered as a buzzer by the voltage from the USB buss, so that it just functions as a switch.

Alternately - is anyone familiar with a better switching system for this application? What I need to do is make a set of pads, which can be hit with a stick, which each contain a switch which will connect the two poles of the Keyboard IC

Something along these lines:-

http://www.plugandwear.com/default.asp?mod=cpages&page_id=22

??

Or this kind of thing:-

 

Yangui

Joined Oct 3, 2015
8
To stop it buzzing you could put diode in series , but may not solve your problem of switching by itself , you will need an amplifier stage .
An alternative to Velostat is conductive foam used in packing IC's as an EMI shield , I have used this foam in a project as a variable resistance pressure mat.
 
Top