Piezo Switch in full wave rectifier circuit?

[michael557]

Hello

I am doing a project for schoola nd I wanted to use piezo disc as a switch for a full wave rectifier circuit...

I want to make a small device powered by a few coin batteries with an LED light... I want to create switch using piezo so when you tap it it would work like a microswitch... so you press it it allows the energy to flow from the batteries into capacitor and form there into LED...

However I am not sure how to utilize the piezo disk to temporarly switch on the circuit...

I hope its simpel and require s alittle components... The device Ia m makign has to be very simple to make and small....

Thank you

Milo

 

[audioguru]

A piezo disc has a current that is too low to light an LED so it must be amplified by a transistor.
A tap on a piezo disc produces a pulse with such a short duration that you probably will not see the LED light up.
Maybe you want the LED to light and stay lighted until the piezo is tapped again which turns off the LED.

So you need a single transistor amplifier that feeds a flip-flop circuit.

 

[michael557]

thanks for the reply...

I think i didnt explain properly.... The piezo disc will be used as a SWITCH.... For example... Say u wanted to switch the lights in your room you use that switch on the wall.... I wants to replace that switch with piezo disc...

As i said i will have a set of batteries but i need the piezo to act as a switch.

But i dont k ow how to use piezo as a switch...

 

[crutschow]

I think i didnt explain properly.... The piezo disc will be used as a SWITCH.... For example... Say u wanted to switch the lights in your room you use that switch on the wall.... I wants to replace that switch with piezo disc...

As i said i will have a set of batteries but i need the piezo to act as a switch.

But i dont k ow how to use piezo as a switch...

You explained it properly. But just because you want something doesn't mean it can be done.

As Uncle $crooge said, a piezo is not a switch. It generates a small amount of current when pressed which can be used to control a switch using the method he noted.

 

[peufeu]

> A piezo disc has a current that is too low to light an LED

FYI, a 1" diamater piezo directly connected to a high brightness red LED will definitely produce a visible (quite strong actually) flash if you tap it with your finger (or hit it against the table) ; the more violent you get, the more light !

Anyway, to use it as a switch you'd need a rather strong debouncing (since the thing resonates a lot) and something like a flip-flop to switch states (on/off).

 

[audioguru]

I don't know why the title of this thread talks about a full-wave rectifier.
A piezo produces a short duration pulse that is not a switch. The person posting the thread needs the debounced piezo to flip a flip-flop circuit each time the piezo is pressed. Then the flip-flop circuit needs to activate a relay or triac that turns on and off the light in his room.

I have no idea why he chose a piezo instead of an ordinary light switch.

 

[peufeu]

> I don't know why the title of this thread talks about a full-wave rectifier.

Yeah.

> I have no idea why he chose a piezo instead of an ordinary light switch.

Hm, anyone's guess it would make a nice watertight switch for the bathroom light, though.