Weird piezo driver

[DaveC]

http://imgur.com/Trvs5mk

This is a beeper piezo in a Fluke 117 DMM which quite beeping. Scoped the
piezo’s pads and... nothing.

An inverter (from the CD4069) is connected across the piezo. Guess I don’t
understand anything about driving piezos.

Is this a standard practice?
Cheers.

 

[N_Cook]

On 16/05/2016 07:36, DaveC wrote:

http://imgur.com/Trvs5mk

This is a beeper piezo in a Fluke 117 DMM which quite beeping. Scoped the
piezo’s pads and... nothing.

An inverter (from the CD4069) is connected across the piezo. Guess I don’t
understand anything about driving piezos.

Is this a standard practice?
Cheers.

My Fluke 77, will beep when the battery is low but not low enough to
trigger the LCD legend, presumably drift over time

 

[Clifford Heath]

On 16/05/16 16:36, DaveC wrote:

This is a beeper piezo in a Fluke 117 DMM which quite beeping. Scoped the
piezo’s pads and... nothing.

Did you mean that "it quit beeping"? If so, you aren't going to hear
anything.

An inverter (from the CD4069) is connected across the piezo. Guess I don’t
understand anything about driving piezos.

The Fluke should be producing a square wave, say 1KHz,
across the piezo. The piezo itself looks like a mid-sized
capacitor; you won't get any DC resistance reading through
it. They are extremely high resistance devices.

If you touch 9v to either side of the piezo, you should
hear it click, and click again when you disconnect.
The Fluke does that too, but fast.

 

[Tauno Voipio]

On 16.5.16 09:36, DaveC wrote:

http://imgur.com/Trvs5mk

This is a beeper piezo in a Fluke 117 DMM which quite beeping. Scoped the
piezo’s pads and... nothing.

An inverter (from the CD4069) is connected across the piezo. Guess I don’t
understand anything about driving piezos.

Is this a standard practice?
Cheers.

You'll get AC drive when you drive one side with a logic signal
and the other side with the same signal inverted.

--

-TV

 

[Spehro Pefhany]

On Sun, 15 May 2016 23:36:38 -0700, the renowned DaveC <not@home.cow>
wrote:

http://imgur.com/Trvs5mk

This is a beeper piezo in a Fluke 117 DMM which quite beeping. Scoped the
piezo’s pads and... nothing.

An inverter (from the CD4069) is connected across the piezo. Guess I don’t
understand anything about driving piezos.

Is this a standard practice?
Cheers.

If you put an inverter across the piezo you get double the supply
voltage drive - push-pull. Not uncommon. Typically you'd drive each
side with two paralleled inverters and use another inverter to invert
the input to one pair.

The piezo element looks something like a ceramic capacitor
electrically. A series capacitor is often used.



--sp


--
Best regards,
Spehro Pefhany
Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8

 

[DaveC]

On 16 May 2016, Clifford Heath wrote

> Did you mean that "it quit beeping"?

Yes, “quit” beeping.

Thanks.

 

[Kevin McMurtrie]

In article
<0001HW.1CE9A1F6001F2AB511837A3CF@news.eternal-september.org>,
DaveC <not@home.cow> wrote:

http://imgur.com/Trvs5mk

This is a beeper piezo in a Fluke 117 DMM which quite beeping. Scoped the
piezo’s pads and... nothing.

An inverter (from the CD4069) is connected across the piezo. Guess I don’t
understand anything about driving piezos.

Is this a standard practice?
Cheers.

Piezo drivers have a high impedance so they need high voltages. One
side of that piezo element is driven with the signal source and the
other side is driven with the inverted signal. That doubles the drive
voltage so it's loud enough to hear.

--
I will not see posts from astraweb, theremailer, dizum, or google
because they host Usenet flooders.