Piezzo siren/alarm

[ben999]

@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!!! :scream: 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 :zipper_mouth_face:

[FotoFieber]

@ben999 said in Piezzo siren/alarm:

@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

I try to simplify: Take a 1 kOhm resistor and attach each side of it to another pin of the piezo. Don't change anything else.

[ben999]

@fotofieber :grin: oh yes i got that one correct :stuck_out_tongue_winking_eye:

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" :joy:

[ben999]

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... :thinking_face:

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 :wink:

[FotoFieber]

@ben999 said in Piezzo siren/alarm:

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

Cool, you sorted it out! The resistor may only help in an DC setup (one output from the arduino). In your AC setup it is useless.

[ben999]

@fotofieber gosh that a good analysis :+1: 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

[FotoFieber]

@ben999
You could try DC (one output) with 12V to the piezo. If you want to use only 5V, the AC solution should be louder, as it gets 10V difference to the piezo.

I usually stop optimizing, when it is good enough. If AC is enough, go with it. :)

[ben999]

@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 :smiley:

[ben999]

back at it !

I got my LCD microscope out and tried to reverse-engineer the original board. I should have done that to start with.

I drew that circuit on www.falstad.com (this link takes you to my actual circuit) and got several kV out of the simulation lol.

I used the original transformer: i could only measure resistance, so 5,5ohms on primary side, and 195ohms on secondary.

First transistor hooked to wave generator is J3Y. I replaced it with a BC547 (the "copy-paste" engineer hidden inside my head told me it's fairly close lol).

Second transistor is labeled J41CG and seems pretty strong to me so i replaced it with TIP120 .

Next I put all these components onto the breadboard, and load my favourite Nano with this sketch :

const int buzzerPin = 9;
int i = 0;
unsigned long duration = 1000;

void setup() {
  pinMode(buzzerPin, OUTPUT);
}

void   loop() {
  for (i = 1000; i < 5000; i++) {
    tone(buzzerPin, i, duration);
  }
  for (i = 5000; i > 1000; i--) {
    tone(buzzerPin, i, duration);
  }
}

That is ever so LOUD !!

So this is plenty good enough for my little project !

[TheoL]

There are also a lot of circuits using 555 timers and some old CMOS or TTL chips that easily create the oscilation you need. It draws a bit more power when the piezo is active. But for me that's worth it, because it gets rid of the complication in the code.
And is you have a bad MySensors radio connection, MySensors will keep executing code that might interrupt code. Which is annoying for applications like this, because it will interfere with your piezo sound. That's why I prefer a hardware solution or an active piezo buzzer. The ones that have a range from 3.3V to 24V are usually very load at 24V. They can be driven with a simple fet.

At least that's how I look at electronics now, don't jump to a software solution when some old skool electronics make your life easier.

But I love the project!