Next Newby Question - Piezos

Posted by MadGomer on July 3, 2010 at 3:38pm

Stopped at Radio Shack on my way home today to grab a Piezo buzzer.   I think I may have grabbed the wrong one.  Part number is 273-0060, and when I cracked open the lid, in addition to the piezo disc, there is a small circuit board (same size as the piezo disc) connected to the disc with 3 fine copper leads.  The circuit board has 3 little resistors on it and another little component.  The buzzer only has two wires coming out of the case.

 

So, question is, will this one work in my CBG, and if so, do I keep the circuit board on it or cut it off & run my leads from the jack directly to the piezo disc?  If the latter, would also appreciate some advice on which of the three contact points I should solder the leads to on the piezo disk.  THANKS!

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Replies

  • Fitzhugh July 9, 2010 at 3:44pm
    Just a thought: I pulled the buzzer out of a smoke detector that was not in use - the landlord came and put in new ones and I rescued the old ones last year. A smoke detector buzzer might be more convenient to get to than radio shack, but only until you burn down the place. I thought to add this when I realized I'd left the soldering iron plugged in for over a day, in a house filled with four legged disasters.
  • Scott L July 8, 2010 at 6:58pm
    Radio Shack does carry one without the driver circuit, it's a dollar cheaper I think so no major deal, you can just remove the driver circuit or bypass it like others have mentioned. I picked one up the other day from there and it said "needs driver circuit" on it and was a buck cheaper. $1.99 I think, the one you bought was likely $2.99.
  • Fitzhugh July 7, 2010 at 5:49pm
    I eliminated the board. The contacts were soldered to the board but just press-fit in a plastic housing that contained the disk. Inside the housing the acted like springs and pressed against the disk.

    Soldering was not bad using some rosin flux, rather hard without. It looked like there might be a super thin surface layer of some material on the two contact points, material I possibly didn't want to remove. Either that or it was oxidation, and I DID want to remove it. I split the difference and very very very lightly scruffed the disk where I planned to solder using 800 grit sandpaper I use for chisel sharpening (800, not 80!). It might have helped, the rosin probably was all that did. I had a joint fail when I stepped on the cord while walking, otherwise they held fine.
  • MadGomer July 7, 2010 at 7:32am
    Fitzhugh - did you end up leaving the circuit board with the piezo disk & just using red & black on the jack or did you eliminate the board? Thanks!
  • Fitzhugh July 7, 2010 at 6:02am
    The photo almost matches what I have, differing only in inconsequential details, while the diagram certainly does. Seems like you (and I) have a self-driving piezo, and the feedback mechanism sure makes sense.

    This was my first time amping my first cbg so when I tripped over the wire and pulled loose one soldered connection I had to just ignore it and play and play and never got around to re-soldering the wire. It was the small section. I do think combining the two might be worth it since the tones were different. I'll try tomorrow.


    thanks for posting the explanation.
  • Mark July 7, 2010 at 5:49am
    I think I might have figured out what you've got. The piezos with two sections (and three leads) seem to be designed for use in buzzers which work on the basis of what is known as "self drive oscillation mode". See the following diagram from the Velleman website:

    transducers.jpg


    I think what happens is that one part of the disc (presumably the bigger section) works as a speaker while the other section works as a pickup. All you then need is a simple bit of electronics to create a feedback loop with some amplification in it and the unit will generate a tone.

    The alternative way to make a piezo buzzer is with the plain two-lead piezos we are more familiar with, where you just use the unit in a similar way to a speaker.
  • petey twofinger July 7, 2010 at 4:43am
    sure , that lil section would seem to have a lesser or at least different freq response .

    mess around with it and let us know what gives .

    maybe i will run into one of those someday .
  • MadGomer July 6, 2010 at 7:32pm
    Here's a fuzzy photo to take a look at. The lead coming off the metal goes to black, the lead on the large white area is going to the M terminal on the board, and the lead from the smaller white area goes to the "F" terminal.

    petey twofinger said:
    i googled dual tone piezo , saw one that said "constant and beeping tones" , i guess i would do a test , maybe you could use a switch or even get lucky with your pot idea .


    you may get best results doing it in parallel .

    youd have to monkey around .

    never saw one with 3 wires though .
  • petey twofinger July 6, 2010 at 4:30pm
    i googled dual tone piezo , saw one that said "constant and beeping tones" , i guess i would do a test , maybe you could use a switch or even get lucky with your pot idea .

    you may get best results doing it in parallel .

    youd have to monkey around .

    never saw one with 3 wires though .
  • Fitzhugh July 6, 2010 at 4:20pm
    I just pried the buzzer out of a smoke alarm and found three contacts on the piezo. When tap testing it with each combination I get two distinct sounds, one fuller and lower and one much more on the treble end. I think it was made to make two different noises, so is really two peizos combined. Tell me if this sounds wrong to anyone. The alarm made both chirp noises when the battery was low and, of course, the horrid ear splitting alarm noise. I wonder if I can (easily) ad a knob to mix between the two as a pseudo tone knob?

    Perhaps your piezo is like this. I'll post photos in a little while.
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