@fotofieber DC+ one output is really poor and voltage has no impact on noise. I have tested with up to 6S LiPo and there's absolutely no gain as compared to 5V DC

AC+ two outputs is a game changer! Much louder right from +/-5V and really a killer @ +/-12V.

So that's it: the first iteration of this project will go for a step-up converter from 5V up to 12V for the piezo speaker.

Thanks folks!

EDIT: could someone suggest a MOSFET (or transistor) that could be used in lieu of the huge (and probably over-sized) TIP120 (that where there, waiting in the drawer ). Through-hole is my league. SMD is a bit of a struggle (welding, machining pcb, ...)

Thanks again

@fotofieber gosh that a good analysis that makes a lot of sense
Then i can picture things better:

• one output with 0 et +5V is considered as DC
• two output pulling differentially -5V to +5V... looks like a sin curbe... so it's AC !

Breadboard is out and still cabled, i'll have a go asap and confirm

Thanks again for your knowledge

Guys,

Thanks all a lot for your input.

Seems sorted :

• differential drive (ToneAC)
• transistor (TIP120 in my case, not sure it's my best move)
• 3S louder than 2S, itself louder than 1S

Schematic TIP120 and 1k resistors

I did also put a 1k resistor in between the piezo speaker pins... but it lowered the tone by quite a lot...

To be tested

I'll have a go with an inductance to see what " then you double the swing" means... double the loudness or double the speed ?

Thanks again, people involved

@fotofieber oh yes i got that one correct

It was more about how to size the inductor and stuff. Guys on these forums know their sh*t, they dont go into much details: "just stick a thing there and you'll be good"

@mfalkvidd oh yeah I forgot about that one!!! Thanks a lot! I have used this with a Mega for who-knows-what-reason in the past but completely forgot about it! ToneAC still in the race then, thanks again

@fotofieber thanks a lot, but that thread is for high-level hobbyists!!! Schematics, yummy!!!
"replace the resistor with an inductor then you double the swing" but no figures... i'll google that and see where it gets me...
I dont even know the specs of my piezo

@fotofieber hi thank you for your message

I was coming back here to share my findings.... been playing with... ToneAC

Yes you're right, differential drive makes a hell of a difference! each pin of the piezo speaker are connected to its own arduino output (serial resistor on one pin though) that send the same signal in opposition as to get a differential movment.

But i don't quite get it :

• driving the piezo speaker with up to 25V doesn't improve noise level at all
• switching to differential drive @5V (so it's a 10V potential peak-to-peak) opens hell's doors wide open

That's the part i dont understand. I'll carry on investigating.

Still: noise level is a bit below as compared to same pizeo speaker connected to original alarm enclosure...
I might have a go with transistors and try a differential of 2S or 3S LiPo.
Also waiting for my oscilloscope to find out!

And lastly: ToneAC uses pins 9 and 10... so it's a NO-NO with nRF24
Enters... ToneAC2. It's inferior (CPU cycle, accuracy, lower freq) in many points except that pins are configurable.

More soon...

@bjacobse thanks for clarification

No smoke came out of mine under 25V DC so i guess it's ok

And yes, i shall cut open an old smoke alarm, you're right.

Thanks a lot

@mfalkvidd Something puzzling me here, can i please borrow your brain for a sec ?

@bjacobse mentionned that his small piezzo buzzer could take up to 30V...

So i had a go with my own buzzer and the previous schematic with 1S LiPo up to 6S LiPo (close to 25V) and 440Hz up to 32kHz (max Tone() )

No change there. Still the same noise i got with a smaller transistor and a 5V power supply.

Tone() changes the width of the modulation (X scale), so i get different tones.
Voltage of the power suppy changes the power going through the piezzo disc... but it doesn't get any louder.

So what is the magic to get a loud buzzer? I shall get my oscilloscope within a month, so until then i keep scratching my head !!

@fotofieber woooooooooooooooow

I searched last night for something similar (iOS and BT) but couldn't find one

So i bought a cheap portable one on aliExpress

https://fr.aliexpress.com/item/JYE-Tech-DSO138-13805K-Mini-Digital-Oscilloscope-DIY-Kit-SMD-Parts-Pre-soldered-Electronic-Learning-Set/32919633946.html?spm=a2g0w.10010108.1000016.1.6349de7cOC8Hnf&isOrigTitle=true

We're not talking about the same amount of money there...

But i'm now deeeeeeeeeply in love and will consider PokitMeter for my next workshop toy

Thank you for the link

@mfalkvidd oh thanks for quick reply and links.

A bit off-topic here: would you rather go for a computer version or a portable one ?