Audio Work - Piezo Driver Updates

Post by **Rob Thomson** » Tue Jan 10, 2012 7:36 am

Hi all,

I am looking into some updates to the Piezo sound system I built.

The current system has a few minor niggles - that are easy to resolve.

---
1. Dual Queues
The queue system really needs to run two queues. One for background sound. One for play now sounds!
At the moment you can get odd pops and interrupts to the sound when the calls collide.

2. Min & Max frequency ranges
I have found the the Piezo speakers have very distinct frequency ranges at which they operate. You may already have 'heard' the funnies that can occur when you drive them out of range. A typical symptom of this is that the pitch gradually increases.. then suddly goes low again - even though you are telling it to go higher!

I am thinking that the solution will be to replace the 'speaker pitch' option with a minimum and maximum pitch option. Then I drive the sound only in the range between those values.
---

Does anyone have any insight or thoughts on this before I get started?

I actually think I will be able to reduce the whole audio system size during this rework. The system grew organically - and a rework will clean it up. (same interface to class so no real change to core code)

Rob

Flaps 30 · Post by **Flaps 30** » Tue Jan 10, 2012 1:34 pm

Piezo sounders are fussy as to how you feed them. We are feeding them with square waves that is rich in odd harmonics. All sounders have a relatively narrow band of frequencies, where they work efficiently. The particular sounder that I have, has a resonant spot at 5Khz where it works very well. Moving 1Khz either side is fine, anymore and it starts to get messy with low output. This is what I have ----> http://cpc.farnell.com/_/41-pt51l120hlf ... tt=ls00642

The earphone doesn't suffer from any of this ----> http://cpc.farnell.com/_/hk-1s/single-s ... dp/AV12698

Post by **Rob Thomson** » Tue Jan 10, 2012 1:37 pm

I guess the 'best' solution will be a proper speaker driver - rather than a piezo!

Post by **jhsa** » Tue Jan 10, 2012 3:25 pm

should I say it???

only joking

Post by **cre8tiveleo** » Tue Jan 10, 2012 4:03 pm

A nice melodic sound from our radios? Seriously!

So we could use...

And benefit.. from.. maybe.. voice... musical alerts... coooool...

Post by **Rob Thomson** » Tue Jan 10, 2012 4:38 pm

What speaker is that in the picture?

Post by **cre8tiveleo** » Tue Jan 10, 2012 4:57 pm

A small one?

Very low voltage one, I'll have to get the numbers off the speaker and let you know. I had two from an Win Ce PMP / gps unit that i use for Fpv screen, didn't need the speakers , so they got installed into the radio, and they sound loud.

I'll get you the info after work.

Post by **Rob Thomson** » Tue Jan 10, 2012 5:01 pm

Thank you! Been looking for a suitable mini speaker

Flaps 30 · Post by **Flaps 30** » Tue Jan 10, 2012 7:38 pm

CPC Farnell have a few small eight Ohm speakers Rob. Reasonable prices and it easy to deal with them, as they are the public arm of Farnell.

-----> http://cpc.farnell.com/jsp/search/brows ... 12699+2005

One that really took my fancy was this one ----> http://cpc.farnell.com/visaton/k-16-50- ... is%20Range It has a fairly high impedance (easy to drive in our case) and it is small. The height is (as stated in the data file) 3.5 mm and the diameter is 16 mm

Post by **cre8tiveleo** » Tue Jan 10, 2012 8:28 pm

Ls0312 and 13 are what i have, i just have to check the size, but those would be them from the link.

Post by **Rob Thomson** » Tue Jan 10, 2012 9:57 pm

Are you using these direct? No extra drive circuit in play?

Sent from my iPhone using Tapatalk

Post by **cre8tiveleo** » Tue Jan 10, 2012 10:35 pm

Mine are 8ohm 1w...

(just zoomed into the picture on the one)

Just the piezo circut thingy that was posted.(just the cap inline) They work fine, no issues... no bad current draw , batteries haven't been charged in over a month too. (using lipo)

The ones on the link are only 200mW.

Clivew · Post by **Clivew** » Wed Jan 11, 2012 1:24 am

These sound good with a fet to drive them http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... OC:GB:1123

wheelspinner20 · Post by **wheelspinner20** » Wed Jan 11, 2012 1:35 am

Just the piezo circut thingy that was posted.(just the cap inline

Can you drag the instructions for that over here please?

Thanks

Pat

wheelspinner20 · Post by **wheelspinner20** » Wed Jan 11, 2012 1:38 am

Also, would it be possible to post a video or maybe a mp3 of what it sounds like???

Post by **cre8tiveleo** » Wed Jan 11, 2012 1:46 am

Sounds just like the stock piezo, since that's the wave form that's being pumped out, just louder and richer.

Hardware guides, drag your mouse over and click, all will be revealed.

I had one of these too, sounded great as well...

Post by **Rob Thomson** » Wed Jan 11, 2012 6:42 am

Some examples using just a regular piezo tweeter

http://www.youtube.com/watch?v=n3gDDmL5Fnc

http://www.youtube.com/watch?v=2yA09EzQa7c

wheelspinner20 · Post by **wheelspinner20** » Fri Jan 13, 2012 2:58 am

blank

Was there supposed to be something there rob??

Post by **Rob Thomson** » Fri Jan 13, 2012 6:45 am

wheelspinner20 wrote:blank

Was there supposed to be something there rob??

See this thread: viewtopic.php?f=3&t=193

SamoaFlyer · Post by **SamoaFlyer** » Sat Jan 14, 2012 4:42 am

Rob,

What is the purpose of the 4.7uF cap in series with your piezo speaker mod? According to the schematic of the main board there is already a 10uF series cap from the MPU pin to the "buzzer" line.

Regarding speaker size, I suggest using the largest size that will fit in the interest of best audio quality, particularly if voice audio is in the eventual plan.

The one I've ordered is : http://www.ebay.com/itm/350520826887?ss ... 1423.l2648

: My Speaker Choice

Post by **cre8tiveleo** » Sat Jan 14, 2012 5:12 am

I'd watch out for that magnet though... 32ohm?

The speakers i use came out of a pmp gps system, running windows ce. Played video, music, and tts gps perfectly.

The ones from the link provided above will be more than capable.

JayPi01 · Post by **JayPi01** » Sat Jan 14, 2012 9:14 am

Found this two speakers in childrens toys. The green one is from a McDonalds toy, the other one from a plush toy. Just seek in your childrens toys for some annoying loud toys that you always wanted to destroy

JayPi01 · Post by **JayPi01** » Sat Jan 14, 2012 9:19 am

Found this two speakers in childrens toys. The green one is from a McDonalds toy, the other one from a plush toy. So just seek your childrens toy for annoying loud toys that you always wanted to destroy

SamoaFlyer · Post by **SamoaFlyer** » Sat Jan 14, 2012 9:41 am

What is your concern about the magnet? All dynamic speakers have them.

The higher impedance will reduce current requirements and drive easier from low power sources.

Generally, the larger the diameter the better the low frequency response with more natural voice rendition.

Bill

HC1969 · Post by **HC1969** » Sat Jan 14, 2012 3:40 pm

MCU load 32 Ohm???
I=5/32=0.156A (156mA)!!!

SamoaFlyer · Post by **SamoaFlyer** » Sat Jan 14, 2012 5:02 pm

With square wave drive average current would be half but compare to an 8 Ohm load. It still needs a buffer/amp but the point is battery current will be a lot less than an 8 Ohm unit.

Bill

Post by **Rob Thomson** » Sat Jan 14, 2012 5:28 pm

Remember too.. Power wise. It only uses power when we have sound events.

Thos are not all time

Rob

Sent from my iPhone using Tapatalk

SamoaFlyer · Post by **SamoaFlyer** » Sun Jan 15, 2012 3:26 am

While awaiting the arrival of the above mentioned speakers, I noticed that the sound exit grill on the front of the 9x actually had quite small holes instead of the slots that first appeared to be open. This would cause an undesired amount of acoustic loading on the speaker cone thereby reducing its frequency response and volume.

A little careful work with a dremel and knife, working on the inside, gave open slots with about five times the area of the original holes. The ouside appearance is unchanged. This gave the immediate benefit of significantly increasing the sound output of the stock buzzer/beeper, which I felt was sorely needed. My old ears don't hear those high frequencies well any more.

I would expect similar results no matter what transducer is used.

Post by **cre8tiveleo** » Sun Jan 15, 2012 3:33 pm

I guess it's a Q/C issue again, on all the 4 radios I have, the grills are all the way through, fully, no blockage. (they all came from one sours, HK) I have mine mounted there, nicely hot glued and sounding magnificant, or as good as a square wave can.

Post by **ShowMaster** » Sun Jan 15, 2012 3:45 pm

I have a BDay card that plays a loud terrible song, but it is loud. I'm thinking of finding the cheapest card that plays music and using the speaker from it. Driver issues? I think I'm going to put my scope on it before tearing it out just to get a level being used to drive it. Then when I install it my 9X and drive it I'll have a reference level to work with if it's too soft or loud. If I need more level is there a fet or transistor driver circuit prefered I should use?
Thanks
SM

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