Piezo's need ac just like speakers. So no i dont currently think i have.

Sorry James, but you have. Piezo sounders work on DC.

I dont mean the whole sounder, i mean the piezo parts (ie the speaker like parts)

You apply apply dc to them then they wont occilate and as such wont make any noise.

can't say I've ever bothered to check but assume a piezo need AC to vibrate,

old sab made from bits (or regalsafe ones) have speakers with a platic cones, same as a driven internal ones

A little snippet

A piezo sounder is a piece of crystal which changes shape (moves) when you apply a voltage across it

No AC is required.

Sorry to use this link but,

http://www.securitywarehouse.co.uk/catalog/index.php?main_page=product_info&products_id=1183

Edited October 15, 201015 yr by Oxo

Yes but there is a driver board in that unit so its a 12v input. But the actually piezos like all piezos run ac. Its like saying car speakers run on dc cos the head unit runs 12v dc

I`ll rephrase, some do work on DC only.

Yes but there is a driver board in that unit so its a 12v input. But the actually piezos like all piezos run ac. Its like saying car speakers run on dc cos the head unit runs 12v dc

you are right James,

the pietzo that makes a noise needs via a driver (for refference you can buy with or without a driver pcb versions from maplins and RS), so some have a pcb built in like a sound bomb other designs have the driver circuit on a pcb externally (thik old flash guards guys)

the pietzo elements usually works on high frequecly signals generated by the driver boards, designed to handle the power

i'm guessing this siren has 2 pietzo's eleiment outputs where each pietzo is on a different ramping square wave cycle (which might be chopped dc), both wired to a common for convenience.

Arfur

Yes i noticed the component specs talking about peak to peak voltage. Id assume 20v + would move it to one position, 0v back to rest and 20v - the other way. Obviosly the element would have to move as quickly as possible between its 2 maxed positions.

I have no idea what voltage the elements themselves run at mind and assume its pretty high to achieve the pressure they do.

5v square iirc,as I said not all need AC.

I`ll go abck to banging head on wall, far easier. Correct and hurts less.

Cannot be bothered to correct spelling.

Edited October 15, 201015 yr by Oxo

two thin crystal discs with diapham in middle (diaphram makes the noise).

introduce electric charge to 1st crystal & it expands, bending diaphram. introduce charge to 2nd & that expands but will only bend diaphram other way if charge on 1st is removed.

effecively applying & removing dc to both discs in an alternating way.

LOL, hope thats clear.

(thats what the driver does - as arf mentioned)