PIEZO VIBRATION SWITCH - HELP CONVERT VOLTAGE TO CLOSE A CON

[Timothy]

I need a VIBRATION SWITCH. I'm trying to make one from a piezo disc
which I got from the inside of a buzzer. When the piezo is vibrated or
bent it creates a voltage. I need to convert this voltage to close a
contact. I tried using an N-type FET transistor with it but the
contacts REMAIN CLOSED for every pulse of the piezo. Maybe it's the
transistor??? I couldn't find the one used from this schematic so I
experemented with a few oter N type FET's.
http://slot-tech-ftp.serveftp.com:8080/pinball/gottlieb/smart%20switch/gottlieb_smart_switch.htms

Please post or email me with any helpful ideas. Thanks in advance.

 

[John Fields]

On 18 Sep 2003 11:53:57 -0700, tim247@ptd.net (Timothy) wrote:

I need a VIBRATION SWITCH. I'm trying to make one from a piezo disc
which I got from the inside of a buzzer. When the piezo is vibrated or
bent it creates a voltage. I need to convert this voltage to close a
contact. I tried using an N-type FET transistor with it but the
contacts REMAIN CLOSED for every pulse of the piezo. Maybe it's the
transistor??? I couldn't find the one used from this schematic so I
experemented with a few oter N type FET's.

---
Chances are the piezo film they're using is poled PVDF, which puts out a
remarkably high voltage when it's flexed properly. If you're flexing
your piezo disc with your finger, what's probably happening is that
you're not flexing it fast enough to generate the voltage needed to turn
the FET on.

Notice that the pinball switch operates when the ball _leaves_ the
switch, so the high voltage is generated when the switch snaps back to
its unflexed position. What you may want to try is to tap your piezo
disc with something hard (like a swizzle stick) and see what happens
then.

Also, you could use a voltage comparator to sense the voltage generated
by the disc, and if you set it right it ought to detect it even if you
pressed it slowly.

--
John Fields

 

[Timothy]

John Fields <jfields@austininstruments.com> wrote in message news:<4qbkmvo0m8qaolsnt003vv1t5dm4r1d36t@4ax.com>...

On 18 Sep 2003 11:53:57 -0700, tim247@ptd.net (Timothy) wrote:

I need a VIBRATION SWITCH. I'm trying to make one from a piezo disc
which I got from the inside of a buzzer. When the piezo is vibrated or
bent it creates a voltage. I need to convert this voltage to close a
contact. I tried using an N-type FET transistor with it but the
contacts REMAIN CLOSED for every pulse of the piezo. Maybe it's the
transistor??? I couldn't find the one used from this schematic so I
experemented with a few oter N type FET's.

---
Chances are the piezo film they're using is poled PVDF, which puts out a
remarkably high voltage when it's flexed properly. If you're flexing
your piezo disc with your finger, what's probably happening is that
you're not flexing it fast enough to generate the voltage needed to turn
the FET on.

Notice that the pinball switch operates when the ball _leaves_ the
switch, so the high voltage is generated when the switch snaps back to
its unflexed position. What you may want to try is to tap your piezo
disc with something hard (like a swizzle stick) and see what happens
then.

Also, you could use a voltage comparator to sense the voltage generated
by the disc, and if you set it right it ought to detect it even if you
pressed it slowly.

The piezo is generating enough voltage to turn the FET on. The problem
is that the FET stays on. Also reversing the polarity on the piezo
turns the FET on as it vibrates in opposite direction.

 

[John Fields]

On 18 Sep 2003 19:16:36 -0700, tim247@ptd.net (Timothy) wrote:

The piezo is generating enough voltage to turn the FET on. The problem
is that the FET stays on. Also reversing the polarity on the piezo
turns the FET on as it vibrates in opposite direction.

---
Sounds like you're charging the gate capacitance of the FET and then not
allowing it to discharge. What does your circuit look like?

--
John Fields

 

[JeffM]

Don't post in ALL-CAPS, retard.