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Electronics => Projects, Designs, and Technical Stuff => Topic started by: djacobow on April 27, 2017, 07:12:00 pm

Title: Very flat, SMD sound making thing?
Post by: djacobow on April 27, 2017, 07:12:00 pm
I'm doing an electronic business card. I know, like everyone else.

Would like to have some beeps and bloops as well as LEDs flashing. I see these cool very flat piezoelectric transducers, but they require a wire to contact the upper plate.

Is there an SMD equivalent? Maybe I'm tying in the wrong terms? I have seen some little SMD buzzer box shaped things, but they're taller than the cr2032 holder that I have decided is the limit for this project.
Title: Re: Very flat, SMD sound making thing?
Post by: evb149 on April 27, 2017, 08:25:38 pm
https://www.digikey.com/en/product-highlight/c/cui/micro-buzzers (https://www.digikey.com/en/product-highlight/c/cui/micro-buzzers)
https://www.digikey.com/catalog/en/partgroup/smt-series/74 (https://www.digikey.com/catalog/en/partgroup/smt-series/74)
https://www.digikey.com/en/product-highlight/m/murata-electronics-north-america/smd-piezoelectric-sounders (https://www.digikey.com/en/product-highlight/m/murata-electronics-north-america/smd-piezoelectric-sounders)
https://www.digikey.com/en/product-highlight/c/cui/buzzers-and-audio-alerts (https://www.digikey.com/en/product-highlight/c/cui/buzzers-and-audio-alerts)
http://www.cui.com/micro-buzzers (http://www.cui.com/micro-buzzers)


I'm doing an electronic business card. I know, like everyone else.

Would like to have some beeps and bloops as well as LEDs flashing. I see these cool very flat piezoelectric transducers, but they require a wait to contact the upper plate.

Is there an SMD equivalent? Maybe I'm tying in the wrong terms? I have seen some little SMD buzzer box shaped things, but they're taller than the cr2032 holder that I have decided is the limit for this project.
Title: Re: Very flat, SMD sound making thing?
Post by: djacobow on April 27, 2017, 11:35:08 pm
Yes, if those are the total of what's out there than none of them are suitable for this purpose.
Title: Re: Very flat, SMD sound making thing?
Post by: RJFreeman on April 28, 2017, 12:07:25 am
two thoughts:
A bare Piezo element soldered to the top surface of the PCB, with a narrow piece of copper tape to the element (you will either need to trim the backing plate where the tape is, or insulate between the copper tape and the backing plate) this will add maybe a couple of mm thickness.

or if this is a problem, get a hole milled (or drilled) in the PCB, sit the element in the hole, carefully run a bead of epoxy around the edge, gluing the back-plate to the PCB.
Or, maybe a better idea, make the hole slightly smaller than the Piezo element, so you can sit the element on the underside of the PCB, then solder around the edge of the back plate, and bridge between the element and a track on the front of the PCB, which again could be done using a small piece of copper tape, in order to keep the design flat.
Title: Re: Very flat, SMD sound making thing?
Post by: evb149 on April 28, 2017, 12:20:24 am
How so?  Some of those I noticed are only 1.9 or 2.0mm high over the PCB.
As far as I know that is not thicker than ANY CR2032 holder that I've seen.
In fact I think they're probably lower profile than a CR2032 itself based on a guesstimate.

You can probably also buy some piezo film (metallized poled kynar) and make something with that maybe operating with a resonator that is formed by a hole in the PCB itself so it'd have "negative thickness" in a sense.  But that would require some effort to make practicable.

You can also make your own transducers.  Look at some of the people that have made tiny motors or things like that.
Possible.  Not generally considered economical / practical but might be fun for a hobby effort.

I guess you could try tearing apart some old hearing aid or smart phone and see what you can salvage and repurpose.
I'm not sure there would be anything that would be practical though.

Yes, if those are the total of what's out there than none of them are suitable for this purpose.
Title: Re: Very flat, SMD sound making thing?
Post by: amitchell on April 28, 2017, 12:23:35 am
Well you could use the Piezo effect of MLCC's to your advantage and use PWM to get them to '"sing". Most fight to get rid of it, I bet you would have no problem amplifying it.

https://product.tdk.com/en/contact/faq/31_singing_capacitors_piezoelectric_effect.pdf?disppage=1&faq_category=02
Title: Re: Very flat, SMD sound making thing?
Post by: Marco on April 28, 2017, 12:28:36 am
You can get bare piezo electric film, use conductive glue to glue copper strips to it.
Title: Re: Very flat, SMD sound making thing?
Post by: DaJMasta on April 28, 2017, 01:33:22 am
Looks like on ebay you can get those circular piezo speaker elements without the plastic housing or the contact leads.  Something like that, or some of the thinner ones above, could be set in a cutout on your PCB for a little extra height.  It looked to me like several of the already-mentioned options would be suitable, so what about your application would demand something they can't provide?  Maybe there's a different direction to be looking if these won't do.
Title: Re: Very flat, SMD sound making thing?
Post by: djacobow on April 28, 2017, 01:58:35 am
This would be fun to play around with. I may noodle.

Well you could use the Piezo effect of MLCC's to your advantage and use PWM to get them to '"sing". Most fight to get rid of it, I bet you would have no problem amplifying it.

https://product.tdk.com/en/contact/faq/31_singing_capacitors_piezoelectric_effect.pdf?disppage=1&faq_category=02
Title: Re: Very flat, SMD sound making thing?
Post by: djacobow on April 28, 2017, 02:00:22 am
How so?  Some of those I noticed are only 1.9 or 2.0mm high over the PCB.

You are right. I should have looked closer. There are some rather low profile ones.

Title: Re: Very flat, SMD sound making thing?
Post by: evb149 on April 28, 2017, 02:12:21 am
The other (non standard) thing you could do is drill a hole (or slot / aperture)  in the PCB and middle-mount a standard low profile transducer though you'd need to have some probably unintended way to attach the contacts to the PCB pads on the "bottom" of the PCB.

That said I know there are "mid board" jacks / connectors as well as LEDs.  It wouldn't surprise me a bit if some low profile transducers (or even battery holders?) are DESIGNED to mount inside a hole in a PCB so that their profile is effectively lower by the thickness of the PCB.
Of course if your PCB is only 0.6mm thick or something it is hardly worth considering.  But for a 1.6mm thick PCB it could be a substantial reduction.

Seems like I have heard of some such thing.. I don't recall where at the moment. 

How so?  Some of those I noticed are only 1.9 or 2.0mm high over the PCB.

You are right. I should have looked closer. There are some rather low profile ones.
Title: Re: Very flat, SMD sound making thing?
Post by: amitchell on April 28, 2017, 02:17:19 am
Something like this would work. As said above mount it in an opening "upside down".


(http://media.futureelectronics.com/passives/buzzers/CMT-1603-CUI-FNT-MED.JPG?m=CqpHAm)
http://www.futureelectronics.com/en/technologies/passives/buzzers/Pages/6028263-CMT-1603-SMT-TR.aspx?IM=0 (http://www.futureelectronics.com/en/technologies/passives/buzzers/Pages/6028263-CMT-1603-SMT-TR.aspx?IM=0)
Title: Re: Very flat, SMD sound making thing?
Post by: djacobow on April 28, 2017, 03:16:49 am
The other (non standard) thing you could do is drill a hole (or slot / aperture)  in the PCB and middle-mount a standard low profile transducer though you'd need to have some probably unintended way to attach the contacts to the PCB pads on the "bottom" of the PCB.

That is an interesting idea. I've done the same with certain tall LEDs before. I do want to minimize the amount of weird assembly, though, as I'll be doing a bunch of these.

I think I have settled on the CUI CSS-0575A-SMT for the time being. It's 1.9mm high over the board.
Title: Re: Very flat, SMD sound making thing?
Post by: djacobow on April 28, 2017, 03:18:02 am
Something like this would work. As said above mount it in an opening "upside down".


(http://media.futureelectronics.com/passives/buzzers/CMT-1603-CUI-FNT-MED.JPG?m=CqpHAm)
http://www.futureelectronics.com/en/technologies/passives/buzzers/Pages/6028263-CMT-1603-SMT-TR.aspx?IM=0 (http://www.futureelectronics.com/en/technologies/passives/buzzers/Pages/6028263-CMT-1603-SMT-TR.aspx?IM=0)

Yes, this would work, and it's a little less tall than the one I'm looking at, though it is bigger. A lot cheaper, too, I notice. Hmm.
Title: Re: Very flat, SMD sound making thing?
Post by: KL27x on April 28, 2017, 09:02:48 pm
Quote
Yes, this would work, and it's a little less tall than the one I'm looking at, though it is bigger. A lot cheaper, too, I notice. Hmm.
16mm x 16mm x 2.6mm? That is huge.

I have a couple I keep on hand. This is the thinnest and it has external solder tabs. I haven't sourced a piezo in 4 or 5 years, now. But knowing how I operate, this was the best combination of small and thin that I could find at that time. So far in this thread, it is still holding up to the competition.

11 x 9 x 1.7mm, 70dBA @5V 4.1kHz
http://www.mouser.com/Search/ProductDetail.aspx?R=254-PB119-ROXvirtualkey12800000virtualkey254-PB119-ROX (http://www.mouser.com/Search/ProductDetail.aspx?R=254-PB119-ROXvirtualkey12800000virtualkey254-PB119-ROX)
One con, if handled roughly without an enclosure, they can break. The adhesive/bond fails and the top plate of the enclosure falls off. They still work, though.

I use a Murata part for a smaller footprint. Can't find the part number or specs right now, but it is slightly taller. I wanna say 9 x 9 x 2mm, but without the external pads. These have yet to fall apart on me.

*edit: here it is PKMCS0909E4000-R1


Title: Re: Very flat, SMD sound making thing?
Post by: blueskull on April 28, 2017, 09:22:34 pm
And if you are really desperate, you can cut a rectangular hole in PCB and make castellated vias for electrical connection, then solder the piezo buried in the PCB hole.
A typical PCB is 1.6mm thick, and if you can get a <=1.6mm thick piezo actuator, then you are looking at zero additional height.
Title: Re: Very flat, SMD sound making thing?
Post by: djacobow on July 26, 2017, 03:41:35 am
In the end I made a version of a business card with a little piezo element, but it was annoying, and I could not really work out what song a business card should play, or if it should have me saying hi or something when you press the button.

I decided instead to make a card without sound, but I wanted a new gimmick, so I added a magnetometer chip and the card works as an electronic compass. I used a 1.6mm pcb and a CR2016 tabbed battery in a hole, so it adds no depth. The tallest things on the board are the buttons and the QFP controller. (This one also has headers I used for debug.) In the second revision I also changed some of the silk to solder mask, so my name over the fill is all shiny. I like it.

Since I'm making these myself, the worst thing about this design is the magnetometer, a QFN that stretches my hand soldering skills.

(https://www.eevblog.com/forum/projects/very-flat-smd-sound-making-thing/?action=dlattach;attach=335279;image)
Title: Re: Very flat, SMD sound making thing?
Post by: DaJMasta on July 26, 2017, 05:09:24 am
Neat that you've got a design that actually does something, not just blinks!

For the QFN, my preference is a little bit of solder paste mashed onto the pads, then a drop of tacky flux in the middle and go at it with the hot air gun.  When the solder is molten it should adjust itself to be centered (thanks, surface tension!) and then a little pressure from the top makes sure any extra solder goes out the sides, where it's easy to wick up.

If you're making a bunch, it may be worthwhile to get a solder paste stencil made to apply it properly for all the SMD stuff.  Then you just tweezer on the bits and heat it in a hot plate or under the hot air gun - a smaller board should be no problem to do in small quantities without a proper oven.
Title: Re: Very flat, SMD sound making thing?
Post by: djacobow on July 26, 2017, 06:18:09 pm
Yeah, I have never used stencils before, but it's time to go to the next level. I have experimented with solder paste, but have found (without using stencils) that I prefer to just work with fine solder when I can. That rules out BGAs as well as QFNs whose leads don't go up and over the edge a bit.

In this case, I tried the just putting solder on the pads and then putting flux on top and the part on top of that and heating, and that pretty much worked, but I had to do some touch up with solder wick to get it right.

I have 9 more to make and I'll try a few different techniques. One thing I learned is do this part first and check it out for shorts and connection before adding anything else to the board.
Title: Re: Very flat, SMD sound making thing?
Post by: DaJMasta on July 26, 2017, 07:15:40 pm
The nice thing about QFNs (well, consolation prize nice thing) is that they still have some pad showing on the side, so especially if you leave the pads long, you can basically tin the pad and get a little to fill that corner like working with castellations on a board.  Sort of the same deal with the fine pitch QFPs, I find it way easier to hand solder them with long pads too because it's easier to drag out from the pin to get rid of bridges.

With LGA or BGA or other parts with pads entirely on the underside, you basically have to do it with paste to get a guaranteed connection.  Tinning the pads heating and pushing can work, but it seems like even with flux it's harder to get this one to make every connection than just with paste.

Also could be worth making a pogo programming jig (or similar) instead of having to use headers - they don't fit well in the form factor  ;)

Something like a card edge connector built into the pcb or just a ZIF socket for programming the micro would do the same job.
Title: Re: Very flat, SMD sound making thing?
Post by: djacobow on July 26, 2017, 10:21:02 pm
I thought about doing a pogo array for programming, but I have discovered that I can get by with the regular headers for a small batch by splaying out a 2x3 header a little bit so that when put into the holes (unsoldered) the bent out pins make a friction contact. This works surprisingly well for the 5-10 seconds I need to program the card. I only soldered the header onto this board because I was programming it over and over as I wrote the software and was getting tired of reseating the header after I've handled the board.

I am thinking of doing a PCBA run for 50-100 cards, and if I do, I'll probably redesign for more streamlined programming: pogo and a programming cable that can power the board while doing so!

Thanks for the soldering advice!